B.S., UC Berkeley, Bioengineering (1996)
Ph.D., UC Berkeley/UCSF, Bioengineering (2001)
Current Research and Scholarly Interests
My research group is focused on applications of emerging functional and molecular imaging techniques in radiation therapy of cancer. In order to integrate these novel imaging procedures with state-of-the-art radiation therapy, a number of issues must be addressed. First, what are the molecular targets that hold the most promise for targeting and monitoring response to radiation therapy, and how can they best be visualized in vivo? Second, what are the limitations of novel imaging techniques that may bear on their application in radiation oncology? Third, how can one display, analyze, and segment multiple three-dimensional datasets to generate target volumes for radiotherapy? And finally, how will the information contained in imaging results of different modalities be integrated into the selection of a treatment course for a patient and subsequently, where appropriate, the specification of an optimized radiation target? These questions comprise my research. Projects that address these topics include the implementation and evaluation of clinical PET/CT imaging for radiation treatment planning, development and validation of novel molecular imaging methods for preclinical and clinical imaging of tumor radiosensitivity and radiation response, development of software for multimodal image analysis, and study of tumor hypoxia and radioresistance in small animal models using a multimodality molecular imaging approach.
Phase I Dose Escalation of Stereotactic Radiosurgical Boost for Locally Advanced Esophageal Cancer
To study the safety and feasibility of stereotactic radiation dose escalation following neoadjuvant chemotherapy with concurrent conventionally fractionated radiation, by evaluating the acute and late toxicity of treatment.
Stanford is currently not accepting patients for this trial. For more information, please contact Laurie Ann Columbo, (650) 736 - 0792.
Molecular and Cellular Analysis of Breast Cancer
The purpose of the study is to investigate the different types and subtypes of cells found in breast tumors. The investigators will do this using a variety of molecular analysis tools that may allow for improved tests. The different types of cells in breast cancer impacts the way individuals respond to various treatments.
Imaging and Biomarkers of Hypoxia in Solid Tumors
We hope to find safer, noninvasive methods for measuring tumor hypoxia. Hypoxia, meaning a lack of oxygen, has been associated strongly with a wide range of human cancers. Hypoxia occurs when tumor growth exceeds the ability of blood vessels to supply the tumor with oxygenated blood. It is currently understood that hypoxic tumors are more aggressive. Current methods for measuring hypoxia include invasive procedures such as tissue biopsy, or insertion of an electrode into the tumor. EF5-PET may be a non-invasive way to make this measurement.
Phase I Trial of Metabolic Reprogramming Therapy for Treatment of Recurrent Head and Neck Cancers
The purpose of this study is to study the effect of the drug DCA (dichloroacetate) on recurrent head and neck cancers. Part of this study will also use EF5 PET scan to study tumor hypoxia.
Stanford is currently not accepting patients for this trial. For more information, please contact Alice Banh, 650-723-1423.
- Cancer Biology Journal Club
CBIO 280 (Spr)
- Cellular and Clinical Aspects of Cancer
CBIO 242 (Spr)
- Molecular Genetic Basis of Cancer
CBIO 240 (Aut)
- Program in Radiation Biology Seminar Series
RADO 244 (Aut, Win)
Independent Studies (14)
- Bioengineering Problems and Experimental Investigation
BIOE 191 (Win, Spr, Sum)
- Directed Investigation
BIOE 392 (Aut, Win, Spr, Sum)
- Directed Reading in Cancer Biology
CBIO 299 (Aut, Win, Spr, Sum)
- Directed Reading in Radiation Oncology
RADO 299 (Aut, Win, Spr, Sum)
- Directed Study
BIOE 391 (Aut, Win, Spr, Sum)
- Early Clinical Experience in Radiation Oncology
RADO 280 (Aut, Win, Spr, Sum)
- Graduate Research
CBIO 399 (Aut, Win, Spr, Sum)
- Graduate Research
RADO 399 (Aut, Win, Spr, Sum)
- Medical Scholars Research
RADO 370 (Aut, Win, Spr, Sum)
- Out-of-Department Directed Reading
BIO 198X (Spr)
- Readings in Radiation Biology
RADO 101 (Aut, Win, Spr, Sum)
PHYSICS 490 (Win, Spr)
- Teaching in Cancer Biology
CBIO 260 (Spr)
- Undergraduate Research
RADO 199 (Aut, Win, Spr, Sum)
- Bioengineering Problems and Experimental Investigation
Prior Year Courses
- Imaging Anatomy in Animal Models
RADO 121 (Aut)
- Molecular, Cellular, and Genetic Basis of Cancer
CBIO 241 (Aut)
- Program in Radiation Biology Seminar Series
RADO 244 (Aut, Win, Spr)
- Imaging Anatomy in Animal Models
COMPMED 121 (Aut)
- Molecular, Cellular, and Genetic Basis of Cancer
CBIO 241 (Win)
- Radiation and Cancer Biology Seminar Series
RADO 244 (Aut, Win, Spr)
- Imaging Anatomy in Animal Models
18F-EF5 PET Is Predictive of Response to Fractionated Radiotherapy in Preclinical Tumor Models.
2015; 10 (10)
We evaluated the relationship between pre-treatment positron emission tomography (PET) using the hypoxic tracer 18F-[2-(2-nitro-1-H-imidazol-1-yl)-N-(2,2,3,3,3- pentafluoropropyl) acetamide] (18F-EF5) and the response of preclinical tumor models to a range of fractionated radiotherapies. Subcutaneous HT29, A549 and RKO tumors grown in nude mice were imaged using 18F-EF5 positron emission tomography (PET) in order to characterize the extent and heterogeneity of hypoxia in these systems. Based on these results, 80 A549 tumors were subsequently grown and imaged using 18F-EF5 PET, and then treated with one, two, or four fraction radiation treatments to a total dose of 10-40 Gy. Response was monitored by serial caliper measurements of tumor volume. Longitudinal post-treatment 18F-EF5 PET imaging was performed on a subset of tumors. Terminal histologic analysis was performed to validate 18F-EF5 PET measures of hypoxia. EF5-positive tumors responded more poorly to low dose single fraction irradiation relative to EF5-negative tumors, however both groups responded similarly to larger single fraction doses. Irradiated tumors exhibited reduced 18F-EF5 uptake one month after treatment compared to control tumors. These findings indicate that pre- treatment 18F-EF5 PET can predict the response of tumors to single fraction radiation treatment. However, increasing the number of fractions delivered abrogates the difference in response between tumors with high and low EF5 uptake pre-treatment, in agreement with traditional radiobiology.
View details for DOI 10.1371/journal.pone.0139425
View details for PubMedID 26431331
Recruitment of circulating breast cancer cells is stimulated by radiotherapy.
2014; 8 (2): 402-409
Radiotherapy (RT) is a localized therapy that is highly effective in killing primary tumor cells located within the field of the radiation beam. We present evidence that irradiation of breast tumors can attract migrating breast cancer cells. Granulocyte-macrophage colony stimulating factor (GM-CSF) produced by tumor cells in response to radiation stimulates the recruitment of migrating tumor cells to irradiated tumors, suggesting a mechanism of tumor recurrence after radiation facilitated by transit of unirradiated, viable circulating tumor cells to irradiated tumors. Data supporting this hypothesis are presented through in vitro invasion assays and in vivo orthotopic models of breast cancer. Our work provides a mechanism for tumor recurrence in which RT attracts cells outside the radiation field to migrate to the site of treatment.
View details for DOI 10.1016/j.celrep.2014.06.011
View details for PubMedID 25017065
Hypoxia in Models of Lung Cancer: Implications for Targeted Therapeutics
CLINICAL CANCER RESEARCH
2010; 16 (19): 4843-4852
To efficiently translate experimental methods from bench to bedside, it is imperative that laboratory models of cancer mimic human disease as closely as possible. In this study, we sought to compare patterns of hypoxia in several standard and emerging mouse models of lung cancer to establish the appropriateness of each for evaluating the role of oxygen in lung cancer progression and therapeutic response.Subcutaneous and orthotopic human A549 lung carcinomas growing in nude mice as well as spontaneous K-ras or Myc-induced lung tumors grown in situ or subcutaneously were studied using fluorodeoxyglucose and fluoroazomycin arabinoside positron emission tomography, and postmortem by immunohistochemical observation of the hypoxia marker pimonidazole. The response of these models to the hypoxia-activated cytotoxin PR-104 was also quantified by the formation of ?H2AX foci in vitro and in vivo. Finally, our findings were compared with oxygen electrode measurements of human lung cancers.Minimal fluoroazomycin arabinoside and pimonidazole accumulation was seen in tumors growing within the lungs, whereas subcutaneous tumors showed substantial trapping of both hypoxia probes. These observations correlated with the response of these tumors to PR-104, and with the reduced incidence of hypoxia in human lung cancers relative to other solid tumor types.These findings suggest that in situ models of lung cancer in mice may be more reflective of the human disease, and encourage judicious selection of preclinical tumor models for the study of hypoxia imaging and antihypoxic cell therapies.
View details for DOI 10.1158/1078-0432.CCR-10-1206
View details for Web of Science ID 000282647900017
View details for PubMedID 20858837
DEVELOPMENT OF A MICRO-COMPUTED TOMOGRAPHY-BASED IMAGE-GUIDED CONFORMAL RADIOTHERAPY SYSTEM FOR SMALL ANIMALS
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2010; 78 (1): 297-305
To report on the physical aspects of a system in which radiotherapy functionality was added to a micro-computed tomography (microCT) scanner, to evaluate the accuracy of this instrument, and to and demonstrate the application of this technology for irradiating tumors growing within the lungs of mice.A GE eXplore RS120 microCT scanner was modified by the addition of a two-dimensional subject translation stage and a variable aperture collimator. Quality assurance protocols for these devices, including measurement of translation stage positioning accuracy, collimator aperture accuracy, and collimator alignment with the X-ray beam, were devised. Use of this system for image-guided radiotherapy was assessed by irradiation of a solid water phantom as well as of two mice bearing spontaneous MYC-induced lung tumors. Radiation damage was assessed ex vivo by immunohistochemical detection of gammaH2AX foci.The positioning error of the translation stage was found to be <0.05 mm, whereas after alignment of the collimator with the X-ray axis through adjustment of its displacement and rotation, the collimator aperture error was <0.1 mm measured at isocenter. Computed tomography image-guided treatment of a solid water phantom demonstrated target localization accuracy to within 0.1 mm. Gamma-H2AX foci were detected within irradiated lung tumors in mice, with contralateral lung tissue displaying background staining.Addition of radiotherapy functionality to a microCT scanner is an effective means of introducing image-guided radiation treatments into the preclinical setting. This approach has been shown to facilitate small-animal conformal radiotherapy while leveraging existing technology.
View details for DOI 10.1016/j.ijrobp.2009.11.008
View details for Web of Science ID 000281304600041
View details for PubMedID 20395069
RT_Image: An open-source tool for investigating PET in radiation oncology
TECHNOLOGY IN CANCER RESEARCH & TREATMENT
2007; 6 (2): 111-121
Positron emission tomography (PET) has emerged as a valuable imaging modality for the diagnosis and staging of cancer. However, despite evidence that PET may be useful for defining target volumes for radiation therapy, no standardized methodology for accomplishing this task exists. To facilitate the investigation of the utility of PET imaging in radiotherapy treatment planning and accelerate its integration into clinical radiation oncology, we have developed software for exploratory analysis and segmentation of functional imaging datasets. The application, RT_Image, allows display of multiple imaging datasets and associated three-dimensional regions-of-interest (ROIs) at arbitrary view angles and fields of view. It also includes semi-automated image segmentation tools for defining metabolically active tumor volumes that may aid creation of target volumes for treatment planning. RT_Image is DICOM compliant, permitting the transfer of imaging data and DICOM-RT structure sets between the application and treatment planning software. RT_Image has been used by radiation oncologists, nuclear medicine physicians, and radiation physicists to analyze over 200 PET datasets. Novel segmentation techniques have been implemented within this programming framework for therapy planning and for evaluation of molecular imaging-derived parameters as prognostic indicators. RT_Image represents a freely-available software base on which further investigations of the utlity of PET and molecular imaging in radiation oncology may be built. The development of tools such as this is critical in order to realize the potential of molecular imaging-guided radiation therapy.
View details for Web of Science ID 000245969900007
View details for PubMedID 17375973
Quantitative and qualitative analysis of [(18)F]FDG and [(18)F]FAZA positron emission tomography of head and neck cancers and associations with HPV status and treatment outcome.
European journal of nuclear medicine and molecular imaging
2016; 43 (4): 617-625
While methods for imaging tumor hypoxia with positron emission tomography (PET) have been developed, optimal methods for interpreting and utilizing these datasets in the clinic remain unclear. In this study, we analyzed hypoxia PET images of head and neck cancer patients and compared imaging metrics with human papilloma virus (HPV) status and clinical outcome.Forty-one patients treated as part of a phase III trial of the hypoxic cytotoxin tirapazamine (TROG 02.02) were imaged with PET using fluorodeoxyglucose (FDG) and fluoroazomycin arabinoside (FAZA). FDG and FAZA PET images were interpreted qualitatively and quantitatively, and compared with tumor T stage, HPV status, and treatment outcome using multivariate statistics.PET signals in the tumor and lymph nodes exhibited significant intra- and inter-patient variability. The FAZA hypoxic volume demonstrated a significant correlation with tumor T stage. PET-hypoxic tumors treated with cisplatin exhibited significantly worse treatment outcomes relative to PET-oxic tumors or PET-hypoxic tumors treated with tirapazamine.Quantitative analysis of FAZA PET yielded metrics that correlated with clinical T stage and were capable of stratifying patient outcome. These results encourage further development of this technology, with particular emphasis on establishment of robust quantitative methods.
View details for DOI 10.1007/s00259-015-3247-7
View details for PubMedID 26577940
Outcomes of Modestly Hypofractionated Radiation for Lung Tumors: Pre- and Mid-Treatment Positron Emission Tomography-Computed Tomography Metrics as Prognostic Factors
CLINICAL LUNG CANCER
2015; 16 (6): 475-485
Modestly hypofractionated radiation therapy (HypoRT; 60-66 Gy in 3-Gy fractions) allows patients with locally advanced thoracic tumors and poor performance status to complete treatment within a shorter period without concurrent chemotherapy. We evaluated the outcomes and imaging prognostic factors of HypoRT.We retrospectively reviewed the data from all patients with primary and metastatic intrathoracic tumors treated with HypoRT from 2006 to 2012. We analyzed the survival and toxicity outcomes, including overall survival (OS), progression-free survival (PFS), local recurrence (LR), and distant metastasis. We also evaluated the following tumor metrics in an exploratory analysis: gross tumor volume (GTV), maximum standardized uptake value (SUVMax), and metabolic tumor volume using a threshold of ≥ 50% of the SUVMax (MTV50%) or the maximum gradient of fluorine-18 fluorodeoxyglucose uptake (MTVEdge). We assessed the association of these metrics and their changes from before to mid-RT using positron emission tomography-computed tomography (PET-CT) with OS and PFS.We identified 29 patients, all with pre-RT and 20 with mid-RT PET-CT scans. The median follow-up period was 15 months. The 2-year overall and non-small-cell lung cancer-only rate for OS, PFS, and LR, was 59% and 59%, 52% and 41%, and 27% and 32%, respectively. No grade ≥ 3 toxicities developed. The median decrease in GTV, SUVMax, and MTVEdge was 11%, 24%, and 18%, respectively. Inferior OS was associated with a larger pre-RT MTVEdge (P = .005) and pre-RT MTV50% (P = .007). Inferior PFS was associated with a larger mid-RT SUVMax (P = .003).These findings add to the growing body of data demonstrating promising outcomes and limited toxicity with HypoRT. The pre- and mid-RT PET-CT metrics could be useful for prognostic stratification in future clinical trials.
View details for DOI 10.1016/j.cllc.2015.01.007
View details for Web of Science ID 000363267500024
View details for PubMedID 25770888
- Molecular Magnetic Resonance Imaging of Tumor Response to Therapy SCIENTIFIC REPORTS 2015; 5
- F-18-EF5 PET Is Predictive of Response to Fractionated Radiotherapy in Preclinical Tumor Models PLOS ONE 2015; 10 (10)
Imaging radiation response in tumor and normal tissue.
American journal of nuclear medicine and molecular imaging
2015; 5 (4): 317-332
Although X-ray computed tomography (CT) and magnetic resonance imaging (MRI) are the primary imaging modalities used in the clinic to monitor tumor response to radiation therapy, multi-modal molecular imaging may facilitate improved early and specific evaluation of this process. Fast and accurate imaging that can provide both quantitative and biological information is necessary to monitor treatment and ultimately to develop individualized treatment options for patients. A combination of molecular and anatomic information will allow for deeper insight into the mechanisms of tumor response, which will lead to more effective radiation treatments as well as improved anti-cancer drugs. Much progress has been made in nuclear medicine imaging probes and MRI techniques to achieve increased accuracy and the evaluation of relevant biomarkers of radiation response. This review will emphasize promising molecular imaging techniques that monitor various biological processes following radiotherapy, including metabolism, hypoxia, cell proliferation, and angiogenesis.
View details for PubMedID 26269771
- The Relationship Between Serial [(18) F]PBR06 PET Imaging of Microglial Activation and Motor Function Following Stroke in Mice MOLECULAR IMAGING AND BIOLOGY 2014; 16 (6): 821-829
The relationship between serial [(18)?F]PBR06 PET imaging of microglial activation and motor function following stroke in mice.
Molecular imaging and biology
2014; 16 (6): 821-829
Using [(18) F]PBR06 positron emission tomography (PET) to characterize the time course of stroke-associated neuroinflammation (SAN) in mice, to evaluate whether brain microglia influences motor function after stroke, and to demonstrate the use of [(18) F]PBR06 PET as a therapeutic assessment tool.Stroke was induced by transient middle cerebral artery occlusion (MCAO) in Balb/c mice (control, stroke, and stroke with poststroke minocycline treatment). [18 F]PBR06 PET/CT imaging, rotarod tests, and immunohistochemistry (IHC) were performed 3, 11, and 22 days poststroke induction (PSI).The stroke group exhibited significantly increased microglial activation, and impaired motor function. Peak microglial activation was 11 days PSI. There was a strong association between microglial activation, motor function, and microglial protein expression on IHC. Minocycline significantly reduced microglial activation and improved motor function by day 22 PSI.[18 F]PBR06 PET imaging noninvasively characterizes the time course of SAN, and shows increased microglial activation is associated with decreased motor function.
View details for DOI 10.1007/s11307-014-0745-0
View details for PubMedID 24865401
- Recruitment of Circulating Breast Cancer Cells Is Stimulated by Radiotherapy CELL REPORTS 2014; 8 (2): 401-408
PET Imaging of Stroke-Induced Neuroinflammation in Mice Using [F-18]PBR06
MOLECULAR IMAGING AND BIOLOGY
2014; 16 (1): 109-117
The purpose of this study is to evaluate the 18 kDa translocator protein (TSPO) radioligand [(18)F]N-fluoroacetyl-N-(2,5-dimethoxybenzyl)-2-phenoxyaniline ([(18)F]PBR06) as a positron emission tomography (PET) imaging biomarker of stroke-induced neuroinflammation in a rodent model.Stroke was induced by transient middle cerebral artery occlusion in Balb/c mice. Dynamic PET/CT imaging with displacement and preblocking using PK111195 was performed 3 days later. PET data were correlated with immunohistochemistry (IHC) for the activated microglial markers TSPO and CD68 and with autoradiography.[(18)F]PBR06 accumulation peaked within the first 5 min postinjection, then decreased gradually, remaining significantly higher in infarct compared to noninfarct regions. Displacement or preblocking with PK11195 eliminated the difference in [(18)F]PBR06 uptake between infarct and noninfarct regions. Autoradiography and IHC correlated well spatially with uptake on PET.[(18)F]PBR06 PET specifically images TSPO in microglial neuroinflammation in a mouse model of stroke and shows promise for imaging and monitoring microglial activation/neuroinflammation in other disease models.
View details for DOI 10.1007/s11307-013-0664-5
View details for Web of Science ID 000329793200014
View details for PubMedID 23836504
The potential of positron emission tomography for intratreatment dynamic lung tumor tracking: A phantom study
2014; 41 (2)
This study aims to evaluate the potential and feasibility of positron emission tomography for dynamic lung tumor tracking during radiation treatment. The authors propose a center of mass (CoM) tumor tracking algorithm using gated-PET images combined with a respiratory monitor and investigate the geometric accuracy of the proposed algorithm.The proposed PET dynamic lung tumor tracking algorithm estimated the target position information through the CoM of the segmented target volume on gated PET images reconstructed from accumulated coincidence events. The information was continuously updated throughout a scan based on the assumption that real-time processing was supported (actual processing time at each frame ≈10 s). External respiratory motion and list-mode PET data were acquired from a phantom programmed to move with measured respiratory traces (external respiratory motion and internal target motion) from human subjects, for which the ground truth target position was known as a function of time. The phantom was cylindrical with six hollow sphere targets (10, 13, 17, 22, 28, and 37 mm in diameter). The measured respiratory traces consisted of two sets: (1) 1D-measured motion from ten healthy volunteers and (2) 3D-measured motion from four lung cancer patients. The authors evaluated the geometric accuracy of the proposed algorithm by quantifying estimation errors (Euclidean distance) between the actual motion of targets (1D-motion and 3D-motion traces) and CoM trajectories estimated by the proposed algorithm as a function of time.The time-averaged error of 1D-motion traces over all trajectories of all targets was 1.6 mm. The error trajectories decreased with time as coincidence events were accumulated. The overall error trajectory of 1D-motion traces converged to within 2 mm in approximately 90 s. As expected, more accurate results were obtained for larger targets. For example, for the 37 mm target, the average error over all 1D-motion traces was 1.1 mm; and for the 10 mm target, the average error over all 1D-motion traces was 2.8 mm. The overall time-averaged error of 3D-motion traces was 1.6 mm, which was comparable to that of the 1D-motion traces. There were small variations in the errors between the 3D-motion traces, although the motion trajectories were very different. The accuracy of the estimates was consistent for all targets except for the smallest.The authors developed an algorithm for dynamic lung tumor tracking using list-mode PET data and a respiratory motion signal, and demonstrated proof-of-principle for PET-guided lung tumor tracking. The overall tracking error in phantom studies is less than 2 mm.
View details for DOI 10.1118/1.4861816
View details for Web of Science ID 000331213300021
View details for PubMedID 24506609
Modality comparison for small animal radiotherapy: a simulation study.
2014; 41 (1): 011710-?
Small animal radiation therapy has advanced significantly in recent years. Whereas in the past dose was delivered using a single beam and a lead shield for sparing of healthy tissue, conformal doses can be now delivered using more complex dedicated small animal radiotherapy systems with image guidance. The goal of this paper is to investigate dose distributions for three small animal radiation treatment modalities.This paper presents a comparison of dose distributions generated by the three approaches-a single-field irradiator with a 200 kV beam and no image guidance, a small animal image-guided conformal system based on a modified microCT scanner with a 120 kV beam developed at Stanford University, and a dedicated conformal system, SARRP, using a 220 kV beam developed at Johns Hopkins University. The authors present a comparison of treatment plans for the three modalities using two cases: a mouse with a subcutaneous tumor and a mouse with a spontaneous lung tumor. A 5 Gy target dose was calculated using the EGSnrc Monte Carlo codes.All treatment modalities generated similar dose distributions for the subcutaneous tumor case, with the highest mean dose to the ipsilateral lung and bones in the single-field plan (0.4 and 0.4 Gy) compared to the microCT (0.1 and 0.2 Gy) and SARRP (0.1 and 0.3 Gy) plans. The lung case demonstrated that due to the nine-beam arrangements in the conformal plans, the mean doses to the ipsilateral lung, spinal cord, and bones were significantly lower in the microCT plan (2.0, 0.4, and 1.9 Gy) and the SARRP plan (1.5, 0.5, and 1.8 Gy) than in single-field irradiator plan (4.5, 3.8, and 3.3 Gy). Similarly, the mean doses to the contralateral lung and the heart were lowest in the microCT plan (1.5 and 2.0 Gy), followed by the SARRP plan (1.7 and 2.2 Gy), and they were highest in the single-field plan (2.5 and 2.4 Gy). For both cases, dose uniformity was greatest in the single-field irradiator plan followed by the SARRP plan due to the sensitivity of the lower energy microCT beam to target heterogeneities and image noise.The two treatment planning examples demonstrate that modern small animal radiotherapy techniques employing image guidance, variable collimation, and multiple beam angles deliver superior dose distributions to small animal tumors as compared to conventional treatments using a single-field irradiator. For deep-seated mouse tumors, however, higher-energy conformal radiotherapy could result in higher doses to critical organs compared to lower-energy conformal radiotherapy. Treatment planning optimization for small animal radiotherapy should therefore be developed to take full advantage of the novel conformal systems.
View details for DOI 10.1118/1.4842415
View details for PubMedID 24387502
- Modality comparison for small animal radiotherapy: A simulation study MEDICAL PHYSICS 2014; 41 (1)
Semi-automatic segmentation of subcutaneous tumours from micro-computed tomography images
PHYSICS IN MEDICINE AND BIOLOGY
2013; 58 (22): 8007-8019
This paper outlines the first attempt to segment the boundary of preclinical subcutaneous tumours, which are frequently used in cancer research, from micro-computed tomography (microCT) image data. MicroCT images provide low tissue contrast, and the tumour-to-muscle interface is hard to determine, however faint features exist which enable the boundary to be located. These are used as the basis of our semi-automatic segmentation algorithm. Local phase feature detection is used to highlight the faint boundary features, and a level set-based active contour is used to generate smooth contours that fit the sparse boundary features. The algorithm is validated against manually drawn contours and micro-positron emission tomography (microPET) images. When compared against manual expert segmentations, it was consistently able to segment at least 70% of the tumour region (n = 39) in both easy and difficult cases, and over a broad range of tumour volumes. When compared against tumour microPET data, it was able to capture over 80% of the functional microPET volume. Based on these results, we demonstrate the feasibility of subcutaneous tumour segmentation from microCT image data without the assistance of exogenous contrast agents. Our approach is a proof-of-concept that can be used as the foundation for further research, and to facilitate this, the code is open-source and available from www.setuvo.com.
View details for DOI 10.1088/0031-9155/58/22/8007
View details for Web of Science ID 000327006800010
View details for PubMedID 24168809
Targeted therapies and hypoxia imaging
QUARTERLY JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING
2013; 57 (3): 283-295
Hypoxia-specific cytotoxins have long exhibited considerable promise for treating hypoxic tumors, however recent negative results in large scale clinical trials have highlighted the importance of selecting patients who are most likely to respond using hypoxia imaging methods. This review looks at the available hypoxia-specific cytotoxins and describes how existing hypoxia imaging methods can be best used to predict which tumors will respond. It then surveys prior studies which combine hypoxia-selective cytotoxin treatment with hypoxia imaging, and finally concludes with a discussion of what lessons can be learnt from previous experiences in order to improve the use of these cytotoxic agents in future clinical evaluations.
View details for Web of Science ID 000327366900007
View details for PubMedID 24045624
A novel aldehyde dehydrogenase-3 activator (Alda-89) protects submandibular gland function from irradiation without accelerating tumor growth.
Clinical cancer research
2013; 19 (16): 4455-4464
To determine the effect of Alda-89 (an ALDH3 activitor) on (1) the function of irradiated (RT) submandibular gland (SMG) in mice, (2) its toxicity profile and (3) its effect on the growth of head and neck cancer (HNC) in vitro and in vivo.Adult mice were infused with Alda-89 or vehicle before, during and after RT. Saliva secretion was monitored weekly. Hematology, metabolic profile and post-mortem evaluation for toxicity were examined at the time of sacrifice. Alda-89 or vehicle was applied to HNC cell lines in vitro, and SCID mice transplanted with HNC in vivo with or without radiation; HNC growth was monitored. The ALDH3A1 and ALDH3A2 protein expression was evaluated in 89 HNC patients and correlated to freedom from relapse (FFR) and overall survival (OS).Alda-89 infusion significantly resulted in more whole saliva production and a higher percentage of preserved acini after RT compared to vehicle control. There was no difference in the complete blood count, metabolic profile, and major organ morphology between the Alda-89 and vehicle groups. Compared to vehicle control, Alda-89 treatment did not accelerate HNC cell proliferation in vitro, nor did it affect tumor growth in vivo with or without RT. Higher expression of ALDH3A1 or ALDH3A2 was not significantly associated with worse FFR or OS in either HPV-positive or HPV-negative group.Alda-89 preserves salivary function after RT without affecting HNC growth or causing measurable toxicity in mice. It is a promising candidate to mitigate RT-related xerostomia.
View details for DOI 10.1158/1078-0432.CCR-13-0127
View details for PubMedID 23812668
- A Novel Aldehyde Dehydrogenase-3 Activator (Alda-89) Protects Submandibular Gland Function from Irradiation without Accelerating Tumor Growth CLINICAL CANCER RESEARCH 2013; 19 (16): 4455-4464
Toward a planning scheme for emission guided radiation therapy (EGRT): FDG based tumor tracking in a metastatic breast cancer patient
2013; 40 (8)
Purpose: Emission guided radiation therapy (EGRT) is a new modality that uses PET emissions in real-time for direct tumor tracking during radiation delivery. Radiation beamlets are delivered along positron emission tomography (PET) lines of response (LORs) by a fast rotating ring therapy unit consisting of a linear accelerator (Linac) and PET detectors. The feasibility of tumor tracking and a primitive modulation method to compensate for attenuation have been demonstrated using a 4D digital phantom in our prior work. However, the essential capability of achieving dose modulation as in conventional intensity modulated radiation therapy (IMRT) treatments remains absent. In this work, the authors develop a planning scheme for EGRT to accomplish sophisticated intensity modulation based on an IMRT plan while preserving tumor tracking.Methods: The planning scheme utilizes a precomputed LOR response probability distribution to achieve desired IMRT planning modulation with effects of inhomogeneous attenuation and nonuniform background activity distribution accounted for. Evaluation studies are performed on a 4D digital patient with a simulated lung tumor and a clinical patient who has a moving breast cancer metastasis in the lung. The Linac dose delivery is simulated using a voxel-based Monte Carlo algorithm. The IMRT plan is optimized for a planning target volume (PTV) that encompasses the tumor motion using the MOSEK package and a Pinnacle(3)™ workstation (Philips Healthcare, Fitchburg, WI) for digital and clinical patients, respectively. To obtain the emission data for both patients, the Geant4 application for tomographic emission (GATE) package and a commercial PET scanner are used. As a comparison, 3D and helical IMRT treatments covering the same PTV based on the same IMRT plan are simulated.Results: 3D and helical IMRT treatments show similar dose distribution. In the digital patient case, compared with the 3D IMRT treatment, EGRT achieves a 15.1% relative increase in dose to 95% of the gross tumor volume (GTV) and a 31.8% increase to 50% of the GTV. In the patient case, EGRT yields a 15.2% relative increase in dose to 95% of the GTV and a 20.7% increase to 50% of the GTV. The organs at risk (OARs) doses are kept similar or lower for EGRT in both cases. Tumor tracking is observed in the presence of planning modulation in all EGRT treatments.Conclusions: As compared to conventional IMRT treatments, the proposed EGRT planning scheme allows an escalated target dose while keeping dose to the OARs within the same planning limits. With the capabilities of incorporating planning modulation and accurate tumor tracking, EGRT has the potential to greatly improve targeting in radiation therapy and enable a practical and effective implementation of 4D radiation therapy for planning and delivery.
View details for DOI 10.1118/1.4812427
View details for Web of Science ID 000322735900013
View details for PubMedID 23927305
Cost-effectiveness landscape analysis of treatments addressing xerostomia in patients receiving head and neck radiation therapy.
Oral surgery, oral medicine, oral pathology and oral radiology
2013; 116 (1): e37-51
Head and neck (H&N) radiation therapy (RT) can induce irreversible damage to the salivary glands thereby causing long-term xerostomia or dry mouth in 68%-85% of the patients. Not only does xerostomia significantly impair patients' quality-of-life (QOL) but it also has important medical sequelae, incurring high medical and dental costs. In this article, we review various measures to assess xerostomia and evaluate current and emerging solutions to address this condition in H&N cancer patients. These solutions typically seek to accomplish 1 of the 4 objectives: (1) to protect the salivary glands during RT, (2) to stimulate the remaining gland function, (3) to treat the symptoms of xerostomia, or (4) to regenerate the salivary glands. For each treatment, we assess its mechanisms of action, efficacy, safety, clinical utilization, and cost. We conclude that intensity-modulated radiation therapy is both the most widely used prevention approach and the most cost-effective existing solution and we highlight novel and promising techniques on the cost-effectiveness landscape.
View details for DOI 10.1016/j.oooo.2013.02.017
View details for PubMedID 23643579
- Cost-effectiveness landscape analysis of treatments addressing xerostomia in patients receiving head and neck radiation therapy ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY ORAL RADIOLOGY 2013; 116 (1): E37-E51
Metabolic Tumor Volume Predicts Disease Progression and Survival in Patients with Squamous Cell Carcinoma of the Anal Canal
JOURNAL OF NUCLEAR MEDICINE
2013; 54 (1): 27-32
PET imaging has become a useful diagnostic tool in patients with anal cancer. We evaluated the prognostic value of metabolic tumor volume (MTV) in patients with anal cancer treated with definitive chemoradiotherapy.Patients with anal cancer who underwent PET imaging for pretreatment staging or radiation therapy planning from 2003 to 2011 were included. PET parameters included MTV and maximum standardized uptake value (SUVmax). Total MTV (MTV-T) was defined as the sum of the volumes above a standardized uptake value 50% of the SUVmax within the primary tumor and involved nodes. Kaplan-Meier and Cox regression models were used to test for associations between metabolic or clinical endpoints and overall survival (OS), progression-free survival (PFS), and event-free survival (EFS). Results: Thirty-nine patients were included. Median follow-up for the cohort was 22 mo. Overall, 6 patients died and 9 patients had disease progression. The 2-y OS, PFS, and EFS for the entire cohort were 88%, 74%, and 69%, respectively. Higher MTV-T was associated with worse OS (P = 0.04), PFS (P = 0.004), and EFS (P = 0.002) on univariate analysis. Patients with an MTV greater than 26 cm(3) had worse PFS than did those with an MTV of 26 cm(3) or less (33% vs. 82%, P = 0.003). SUVmax was not prognostic for any outcome. Higher T classification (T3/T4 vs. T1/T2) was associated with worse PFS and EFS. When adjusting for T classification, MTV-T remained a significant predictor for PFS (P = 0.01) and EFS (P = 0.02).MTV-T yields prognostic information on PFS and EFS beyond that of established prognostic factors in patients with anal cancer.
View details for DOI 10.2967/jnumed.112.109470
View details for Web of Science ID 000313606800026
View details for PubMedID 23236018
Metabolic imaging metrics correlate with survival in early stage lung cancer treated with stereotactic ablative radiotherapy.
2012; 78 (3): 219-224
To test whether (18)F-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) imaging metrics correlate with outcomes in patients with stage I non-small cell lung cancer (NSCLC) treated with stereotactic ablative radiotherapy (SABR).Fifty-four patients with stage I NSCLC underwent pre-SABR PET at simulation and/or post-SABR PET within 6 months. We analyzed maximum standardized uptake value (SUV(max)) and metabolic tumor volume defined using several thresholds (MTV50%, or MTV2, 4, 7, and 10). Endpoints included primary tumor control (PTC), progression-free survival (PFS), overall survival (OS) and cancer-specific survival (CSS). We performed Kaplan-Meier, competing risk, and Cox proportional hazards survival analyses.Patients received 25-60 Gy in 1 to 5 fractions. Median follow-up time was 13.2 months. The 1-year estimated PTC, PFS, OS and CSS were 100, 83, 87 and 94%, respectively. Pre-treatment SUV(max) (p=0.014), MTV(7) (p=0.0077), and MTV(10) (p=0.0039) correlated significantly with OS. In the low-MTV(7)vs. high-MTV(7) sub-groups, 1-year estimated OS was 100 vs. 78% (p=0.0077) and CSS was 100 vs. 88% (p=0.082).In this hypothesis-generating study we identified multiple pre-treatment PET-CT metrics as potential predictors of OS and CSS in patients with NSCLC treated with SABR. These could aid risk-stratification and treatment individualization if validated prospectively.
View details for DOI 10.1016/j.lungcan.2012.08.016
View details for PubMedID 23009727
Monte Carlo model of the scanning beam digital x-ray (SBDX) source
PHYSICS IN MEDICINE AND BIOLOGY
2012; 57 (22): 7381-7394
The scanning-beam digital x-ray (SBDX) system has been developed for fluoroscopic imaging using an inverse x-ray imaging geometry. The SBDX system consists of a large-area x-ray source with a multihole collimator and a small detector. The goal of this study was to build a Monte Carlo (MC) model of the SBDX source as a useful tool for optimization of the SBDX imaging system in terms of its hardware components and imaging parameters. The MC model of the source was built in the EGSnrc/BEAMnrc code and validated using the DOSXYZnrc code and Gafchromic film measurements for 80, 100, and 120 kV x-ray source voltages. The MC simulated depth dose curves agreed with measurements to within 5%, and beam profiles at three selected depths generally agreed within 5%. Exposure rates and half-value layers for three voltages were also calculated from the MC simulations. Patient skin-dose per unit detector-dose was quantified as a function of patient size for all three x-ray source voltages. The skin-dose to detector-dose ratio ranged from 5-10 for a 20 cm thick patient to 1 × 10(3)-1 × 10(5) for a 50 cm patient for the 120 and 80 kV beams, respectively. Simulations of imaging dose for a prostate patient using common imaging parameters revealed that skin-dose per frame was as low as 0.2 mGy.
View details for DOI 10.1088/0031-9155/57/22/7381
View details for Web of Science ID 000310838700014
View details for PubMedID 23093305
Postchemoradiotherapy Positron Emission Tomography Predicts Pathologic Response and Survival in Patients With Esophageal Cancer
ELSEVIER SCIENCE INC. 2012: 471-477
To correlate the prechemoradiotherapy (CRT) and post-CRT metabolic tumor volume (MTV) on positron emission tomography (PET) scanning with the pathologic response and survival in patients receiving preoperative CRT for esophageal cancer.The medical records of 37 patients with histologically confirmed Stage I-IVA esophageal cancer treated with CRT with or without surgical resection were reviewed. Of the 37 patients, 21 received preoperative CRT (57%) and 16 received definitive CRT (43%). All patients had a pre-CRT and 32 had a post-CRT PET scan. The MTV was measured on the pre-CRT PET and post-CRT PET scan, respectively, using a minimum standardized uptake value (SUV) threshold x, where x = 2, 2.5, 3, or the SUV maximum × 50%. The total glycolytic activity (TGA(x)) was defined as the mean SUV × MTV(x). The MTV ratio was defined as the pre-CRT PET MTV/post-CRT MTV. The SUV ratio was defined similarly. A single pathologist scored the pathologic response using a tumor regression grade (TRG) scale.The median follow-up was 1.5 years (range, 0.4-4.9). No significant correlation was found between any parameters on the pre-CRT PET scan and the TRG or overall survival (OS). Multiple post-CRT MTV values and post-TGA values correlated with the TRG and OS; however, the MTV(2.5(Post)) and TGA(2.5(Post)) had the greatest correlation. The MTV(2) ratio correlated with OS. The maximum SUV on either the pre-CRT and post-CRT PET scans or the maximum SUV ratio did not correlate with the TRG or OS. Patients treated preoperatively had survival similar compared with those treated definitively with a good PET response (p = 0.97) and significantly better than that of patients treated definitively with a poor PET response (p < 0.0001).The maximum SUV was not a predictive or prognostic parameter. The MTV(2.5) and TGA(2.5) were useful markers for predicting the response and survival on the post-CRT PET scan. The MTV(2) ratio also correlated with survival. Post-CRT PET can potentially guide therapy after CRT.
View details for DOI 10.1016/j.ijrobp.2011.12.029
View details for Web of Science ID 000308062700055
View details for PubMedID 22381904
Prognostic Value of Metabolic Tumor Volume and Velocity in Predicting Head-and-Neck Cancer Outcomes
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2012; 83 (5): 1521-1527
We previously showed that metabolic tumor volume (MTV) on positron emission tomography-computed tomography (PET-CT) predicts for disease recurrence and death in head-and-neck cancer (HNC). We hypothesized that increases in MTV over time would correlate with tumor growth and biology, and would predict outcome. We sought to examine tumor growth over time in serial pretreatment PET-CT scans.From 2006 to 2009, 51 patients had two PET-CT scans before receiving HNC treatment. MTV was defined as the tumor volume ? 50% of maximum SUV (SUV(max)). MTV was calculated for the primary tumor, nodal disease, and composite (primary tumor + nodes). MTV and SUV velocity were defined as the change in MTV or SUV(max) over time, respectively. Cox regression analyses were used to examine correlations between SUV, MTV velocity, and outcome (disease progression and overall survival).The median follow-up time was 17.5 months. The median time between PET-CT scans was 3 weeks. Unexpectedly, 51% of cases demonstrated a decrease in SUV(max) (average, -0.1 cc/week) and MTV (average, -0.3 cc/week) over time. Despite the variability in MTV, primary tumor MTV velocity predicted disease progression (hazard ratio 2.94; p = 0.01) and overall survival (hazard ratio 1.85; p = 0.03).Primary tumor MTV velocity appears to be a better prognostic indicator of disease progression and survival in comparison to nodal MTV velocity. However, substantial variability was found in PET-CT biomarkers between serial scans. Caution should be used when PET-CT biomarkers are integrated into clinical protocols for HNC.
View details for DOI 10.1016/j.ijrobp.2011.10.022
View details for Web of Science ID 000306128100047
View details for PubMedID 22270168
Prognostic PET F-18-FDG Uptake Imaging Features Are Associated with Major Oncogenomic Alterations in Patients with Resected Non-Small Cell Lung Cancer
2012; 72 (15): 3725-3734
Although 2[18F]fluoro-2-deoxy-d-glucose (FDG) uptake during positron emission tomography (PET) predicts post-surgical outcome in patients with non-small cell lung cancer (NSCLC), the biologic basis for this observation is not fully understood. Here, we analyzed 25 tumors from patients with NSCLCs to identify tumor PET-FDG uptake features associated with gene expression signatures and survival. Fourteen quantitative PET imaging features describing FDG uptake were correlated with gene expression for single genes and coexpressed gene clusters (metagenes). For each FDG uptake feature, an associated metagene signature was derived, and a prognostic model was identified in an external cohort and then tested in a validation cohort of patients with NSCLC. Four of eight single genes associated with FDG uptake (LY6E, RNF149, MCM6, and FAP) were also associated with survival. The most prognostic metagene signature was associated with a multivariate FDG uptake feature [maximum standard uptake value (SUV(max)), SUV(variance), and SUV(PCA2)], each highly associated with survival in the external [HR, 5.87; confidence interval (CI), 2.49-13.8] and validation (HR, 6.12; CI, 1.08-34.8) cohorts, respectively. Cell-cycle, proliferation, death, and self-recognition pathways were altered in this radiogenomic profile. Together, our findings suggest that leveraging tumor genomics with an expanded collection of PET-FDG imaging features may enhance our understanding of FDG uptake as an imaging biomarker beyond its association with glycolysis.
View details for DOI 10.1158/0008-5472.CAN-11-3943
View details for Web of Science ID 000307354100004
View details for PubMedID 22710433
Positron Emission Tomography for Predicting Pathologic Response After Neoadjuvant Chemoradiotherapy for Locally Advanced Rectal Cancer
LIPPINCOTT WILLIAMS & WILKINS. 2012: 334-339
To investigate whether before and after chemoradiotherapy (CRT) positron emission tomography (PET) predict for pathologic response after preoperative CRT in patients with locally advanced rectal adenocarcinoma.Thirty-five patients who underwent pre-CRT and post-CRT PET scans before surgery were included. All patients were staged with endoscopic ultrasound or high resolution CT. CRT was given with 50.4 Gy at 1.8 Gy per fraction and concurrent 5-fluorouracil-based chemotherapy. Surgery occurred at a median of 46 days (range, 27 to 112 d) after completing CRT. The maximum standardized uptake value (SUV(max)) and the metabolic tumor volume (MTV) using various minimum SUV thresholds (2, 2.5, 3) on the PET scans (MTV(2.0), MTV(2.5), MTV(3.0)) were determined. Post-CRT PET scans were done 3 to 5 weeks after completion of CRT. Pathologic response was assessed using the tumor regression grade (TRG) scale. Patients with complete or near-complete response (TRG=0 to 1) were considered pathologic responders. The pre-CRT and post-CRT PET scan SUV(max) and MTV values were correlated with TRG. The ?SUV(max) and ?MTV were correlated with TRG.No correlation was seen with SUV(max) (P=0.99), MTV(2.0) (P=0.73), MTV(2.5) (P=0.73), or MTV(3.0) (P=0.31) on the pre-CRT PET between pathologic responders versus nonresponders. No correlation was noted between SUV(max) (P=0.49), MTV(2.0) (P=0.73), MTV(2.5) (P=0.49), or MTV(3.0) (P=0.31) on the post-CRT PET scan and pathologic response. Finally, the ?SUV(max) (P=0.32), ?MTV(2.0) (P=0.99), ?MTV(2.5) (P=0.31), ?MTV(3.0) (P=0.31) did not correlate with pathologic response.Changes seen on PET have limited value in predicting for pathologic response of rectal cancer after preoperative neoadjuvant therapy.
View details for DOI 10.1097/COC.0b013e3182118d12
View details for Web of Science ID 000306599200006
View details for PubMedID 21422989
Validation that metabolic tumor volume predicts outcome in head-and-neck cancer.
International journal of radiation oncology, biology, physics
2012; 83 (5): 1514-1520
We have previously reported that metabolic tumor volume (MTV) obtained from pretreatment (18)F-fluorodeoxydeglucose positron emission tomography (FDG PET)/ computed tomography (CT) predicted outcome in patients with head-and-neck cancer (HNC). The purpose of this study was to validate these results on an independent dataset, determine whether the primary tumor or nodal MTV drives this correlation, and explore the interaction with p16(INK4a) status as a surrogate marker for human papillomavirus (HPV).The validation dataset in this study included 83 patients with squamous cell HNC who had a FDG PET/CT scan before receiving definitive radiotherapy. MTV and maximum standardized uptake value (SUV(max)) were calculated for the primary tumor, the involved nodes, and the combination of both. The primary endpoint was to validate that MTV predicted progression-free survival and overall survival. Secondary analyses included determining the prognostic utility of primary tumor vs. nodal MTV.Similarly to our prior findings, an increase in total MTV of 17 cm(3) (difference between the 75th and 25th percentiles) was associated with a 2.1-fold increase in the risk of disease progression (p = 0.0002) and a 2.0-fold increase in the risk of death (p = 0.0048). SUV(max) was not associated with either outcome. Primary tumor MTV predicted progression-free (hazard ratio [HR] = 1.94; p < 0.0001) and overall (HR = 1.57; p < 0.0001) survival, whereas nodal MTV did not. In addition, MTV predicted progression-free (HR = 4.23; p < 0.0001) and overall (HR = 3.21; p = 0.0029) survival in patients with p16(INK4a)-positive oropharyngeal cancer.This study validates our previous findings that MTV independently predicts outcomes in HNC. MTV should be considered as a potential risk-stratifying biomarker in future studies of HNC.
View details for DOI 10.1016/j.ijrobp.2011.10.023
View details for PubMedID 22270174
Bioluminescence Monitoring of Metastatic Breast Cancer: Quantitative Assessment of Radiation Treatment Effects and Tracking of Tumor Cells
AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS. 2012: 3698-3698
View details for Web of Science ID 000308905804428
Prognostic and Predictive Significance of Plasma HGF and IL-8 in a Phase III Trial of Chemoradiation with or without Tirapazamine in Locoregionally Advanced Head and Neck Cancer
CLINICAL CANCER RESEARCH
2012; 18 (6): 1798-1807
Hepatocyte growth factor (HGF) is a hypoxia-induced secreted protein that binds to cMet and regulates interleukin (IL)-8 expression. We evaluated the role of circulating HGF and IL-8 as prognostic and predictive factors for efficacy of tirapazamine (TPZ), a hypoxic cell cytotoxin.Patients with stages III to IV head and neck cancer were randomized to receive radiotherapy with cisplatin (CIS) or CIS plus TPZ (TPZ/CIS). Eligibility for the substudy included plasma sample availability for HGF and IL-8 assay by ELISA and no major radiation deviations (N = 498). Analyses included adjustment for major prognostic factors. p16(INK4A) staining (human papillomavirus surrogate) was carried out on available tumors. Thirty-nine patients had hypoxia imaging with (18)F-fluoroazomycin arabinoside ((18)FAZA)-positron emission tomography.Elevated IL-8 level was associated with worse overall survival (OS) irrespective of treatment. There was an interaction between HGF and treatment arm (P = 0.053); elevated HGF was associated with worse OS in the control but not in the TPZ/CIS arm. Similar trends were observed in analyses restricted to p16(INK4A)-negative patients. Four subgroups defined by high and low HGF/IL-8 levels were examined for TPZ effect; the test for interaction with arm was P = 0.099. TPZ/CIS seemed to be beneficial for patients with high HGF and IL-8 but adverse for low HGF and high IL-8. Only HGF correlated with (18)FAZA tumor standard uptake value.IL-8 is an independent prognostic factor irrespective of treatment. There is an interaction between HGF and treatment arm. Certain subgroups based on IL-8/HGF levels seemed to do better with TPZ/CIS while others did worse, highlighting the complexity of hypoxia targeting in unselected patients.
View details for DOI 10.1158/1078-0432.CCR-11-2094
View details for Web of Science ID 000301672400037
View details for PubMedID 22383739
The potential for Cerenkov luminescence imaging of alpha-emitting radionuclides
PHYSICS IN MEDICINE AND BIOLOGY
2012; 57 (3): 771-783
Targeted ?-emitting drugs are promising for cancer therapy, but cannot be effectively imaged by conventional techniques. Cerenkov luminescence imaging (CLI) has previously been shown capable of imaging ?(+)- and ?(-)-emitting radionuclides in vivo and could have the potential to image ?-emitters. Cerenkov light production from ?-emitters is through Compton scattering and from farther down the decay chain. This causes the Cerenkov production to vary in time and depend on sample geometry, complicating the interpretation of CLI images. We used the simulation toolkit Geant4 to predict the Cerenkov light output from five ?-emitting radionuclides that have therapeutic potential: (225)Ac, (230)U, (213)Bi, (212)Bi and (212)At. We found that (225)Ac, (213)Bi and (212)Bi produced an order of magnitude more Cerenkov light than (18)F. However, the light from (225)Ac is delayed from the initial decay, possibly decreasing the correlation of the drug and light source. This indicates that CLI will not be helpful in the development of some ?-emitting drugs.
View details for DOI 10.1088/0031-9155/57/3/771
View details for Web of Science ID 000299542000014
View details for PubMedID 22252144
Interim-treatment quantitative PET parameters predict progression and death among patients with hodgkin's disease
We hypothesized that quantitative PET parameters may have predictive value beyond that of traditional clinical factors such as the International Prognostic Score (IPS) among Hodgkin's disease (HD) patients.Thirty HD patients treated at presentation or relapse had staging and interim-treatment PET-CT scans. The majority of patients (53%) had stage III-IV disease and 67% had IPS ? 2. Interim-treatment scans were performed at a median of 55 days from the staging PET-CT. Chemotherapy regimens used: Stanford V (67%), ABVD (17%), VAMP (10%), or BEACOPP (7%). Hypermetabolic tumor regions were segmented semiautomatically and the metabolic tumor volume (MTV), mean standardized uptake value (SUV mean), maximum SUV (SUV max) and integrated SUV (iSUV) were recorded. We analyzed whether IPS, absolute value PET parameters or the calculated ratio of interim- to pre-treatment PET parameters were associated with progression free survival (PFS) or overall survival (OS).Median follow-up of the study group was 50 months. Six of the 30 patients progressed clinically. Absolute value PET parameters from pre-treatment scans were not significant. Absolute value SUV max from interim-treatment scans was associated with OS as determined by univariate analysis (p < 0.01). All four calculated PET parameters (interim/pre-treatment values) were associated with OS: MTV int/pre (p < 0.01), SUV mean int/pre (p < 0.05), SUV max int/pre (p = 0.01), and iSUV int/pre (p < 0.01). Absolute value SUV max from interim-treatment scans was associated with PFS (p = 0.01). Three calculated PET parameters (int/pre-treatment values) were associated with PFS: MTV int/pre (p = 0.01), SUV max int/pre (p = 0.02) and iSUV int/pre (p = 0.01). IPS was associated with PFS (p < 0.05) and OS (p < 0.01).Calculated PET metrics may provide predictive information beyond that of traditional clinical factors and may identify patients at high risk of treatment failure early for treatment intensification.
View details for DOI 10.1186/1748-717X-7-5
View details for Web of Science ID 000301710700001
View details for PubMedID 22260710
GPU-Enabled PET Motion Compensation Using Sparse and Low-Rank Decomposition
2012 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE RECORD (NSS/MIC)
View details for Web of Science ID 000326814203104
Metabolic Tumor Volume is an Independent Prognostic Factor in Patients Treated Definitively for Non-Small-Cell Lung Cancer
CLINICAL LUNG CANCER
2012; 13 (1): 52-58
Fluorine-18 flurodeoxyglucose positron emission tomography (FDG-PET) imaging has rapidly become the standard of care for staging patients with lung cancer. We evaluated the prognostic value of metabolic tumor volume (MTV), a measure of tumor burden on FDG-PET imaging, in patients with non-small-cell lung cancer (NSCLC) treated definitively.A retrospective review identified 61 patients with NSCLC who underwent FDG-PET imaging for pretreatment staging. Metabolically active tumor regions were segmented on the PET scans semiautomatically to calculate the total body MTV. We determined the relationship of overall survival (OS) and progression-free survival (PFS) with MTV in the entire cohort, and in the subgroup treated definitively.The estimated median PFS and OS for the entire cohort were 11.1 months and 18.9 months. Higher MTV was significantly associated with worse OS (P = 0.00075) and PFS (P = 0.00077). For definitively treated patients, when MTV was analyzed as a binary value above or below the median value, 2-year PFS was 60% versus 39.7% (median PFS 34.9 vs. 11.9 months) and 2-year OS was 79.7% versus 33.3% (median OS 41.9 vs. 18.9 months), respectively (log-rank P = 0.12 for PFS and P = 0.066 for OS). When MTV was analyzed as a continuous variable, multivariate Cox proportional hazards analysis demonstrated a trend to worse PFS (hazard ratio [HR] = 1.31; P = 0.12) and significantly worse OS (HR = 1.53; P = 0.018) with increasing MTV after controlling for known prognostic variables.Tumor burden as assessed by MTV yields prognostic information on survival beyond that of established prognostic factors in patients with NSCLC treated definitively.
View details for DOI 10.1016/j.cllc.2011.05.001
View details for Web of Science ID 000299270900008
View details for PubMedID 21703935
Correlation between metabolic tumor volume and pathologic tumor volume in squamous cell carcinoma of the oral cavity
RADIOTHERAPY AND ONCOLOGY
2011; 101 (3): 356-361
To explore the relationship between pathologic tumor volume and volume estimated from different tumor segmentation techniques on (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in oral cavity cancer.Twenty-three patients with squamous cell carcinoma of the oral tongue had PET-CT scans before definitive surgery. Pathologic tumor volume was estimated from surgical specimens. Metabolic tumor volume (MTV) was defined from PET-CT scans as the volume of tumor above a given SUV threshold. Multiple SUV thresholds were explored including absolute SUV thresholds, relative SUV thresholds, and gradient-based techniques.Multiple MTV's were associated with pathologic tumor volume; however the correlation was poor (R(2) range 0.29-0.58). The ideal SUV threshold, defined as the SUV that generates an MTV equal to pathologic tumor volume, was independently associated with maximum SUV (p=0.0005) and tumor grade (p=0.024). MTV defined as a function of maximum SUV and tumor grade improved the prediction of pathologic tumor volume (R(2)=0.63).Common SUV thresholds fail to predict pathologic tumor volume in head and neck cancer. The optimal technique that allows for integration of PET-CT with radiation treatment planning remains to be defined. Future investigation should incorporate biomarkers such as tumor grade into definitions of MTV.
View details for DOI 10.1016/j.radonc.2011.05.040
View details for Web of Science ID 000298894700003
View details for PubMedID 21665308
Facilitating Multimodal Preclinical Imaging Studies in Mice by Using an Immobilization Bed
2011; 61 (6): 499-504
We have designed an immobilization bed that accommodates mice of all ages and sizes, to improve image registration for multimodal scans and for longitudinal preclinical imaging studies. Stationary pegs were placed such that they effectively immobilized mice and reduced set-up time. (22)Na fiducial markers were placed into the pegs at unique depths to provide 3D references to facilitate image registration. Multiple users registered positron emission tomographic (PET) and CT data obtained with and without the bed to examine the effect of the bed on registration accuracy and interuser variability. The image registrations performed by different users were evaluated for their similarity by using the Entropy Correlation Coefficient as a metric. The immobilization bed significantly reduced variations in body movement and interuser variability. Average differences in quantification of tumor PET signal among users when registering images without versus with the fiduciary-marker bed fell from 9.1% to 0.8% for maximal percentage injected dose per gram (%ID/g), from 15.6% to 2.3% for mean %ID/g, and from 9.4% to 0.7% for the 90th percentile of the maximum %ID/g. The bed improves animal immobilization, greatly reduces interuser variability, and supports registration of image data acquired from different imaging sessions.
View details for Web of Science ID 000297910100003
View details for PubMedID 22330576
Targeting GLUT1 and the Warburg Effect in Renal Cell Carcinoma by Chemical Synthetic Lethality
SCIENCE TRANSLATIONAL MEDICINE
2011; 3 (94)
Identifying new targeted therapies that kill tumor cells while sparing normal tissue is a major challenge of cancer research. Using a high-throughput chemical synthetic lethal screen, we sought to identify compounds that exploit the loss of the von Hippel-Lindau (VHL) tumor suppressor gene, which occurs in about 80% of renal cell carcinomas (RCCs). RCCs, like many other cancers, are dependent on aerobic glycolysis for ATP production, a phenomenon known as the Warburg effect. The dependence of RCCs on glycolysis is in part a result of induction of glucose transporter 1 (GLUT1). Here, we report the identification of a class of compounds, the 3-series, exemplified by STF-31, which selectively kills RCCs by specifically targeting glucose uptake through GLUT1 and exploiting the unique dependence of these cells on GLUT1 for survival. Treatment with these agents inhibits the growth of RCCs by binding GLUT1 directly and impeding glucose uptake in vivo without toxicity to normal tissue. Activity of STF-31 in these experimental renal tumors can be monitored by [(18)F]fluorodeoxyglucose uptake by micro-positron emission tomography imaging, and therefore, these agents may be readily tested clinically in human tumors. Our results show that the Warburg effect confers distinct characteristics on tumor cells that can be selectively targeted for therapy.
View details for DOI 10.1126/scitranslmed.3002394
View details for Web of Science ID 000293459700004
View details for PubMedID 21813754
Molecular Imaging of Hypoxia: Strategies for Probe Design and Application
CURRENT ORGANIC SYNTHESIS
2011; 8 (4): 593-603
Tumor hypoxia is a negative prognostic factor and its precise imaging is of great relevance to therapy planning. The present review summarizes various strategies of probe design for imaging hypoxia with a variety of techniques such as PET, SPECT and fluorescence imaging. Synthesis of some important probes that are used for preclinical and clinical imaging and their mechanism of binding in hypoxia are also discussed.
View details for Web of Science ID 000294410500009
The importance of tissue segmentation for dose calculations for kilovoltage radiation therapy
2011; 38 (6): 3039-3049
The aim of this work was to evaluate the effect of tissue segmentation on the accuracy of Monte Carlo (MC) dose calculations for kilovoltage radiation therapy, which are commonly used in preclinical radiotherapy studies and are also being revisited as a clinical treatment modality. The feasibility of tissue segmentation routinely done on the basis of differences in tissue mass densities was studied and a new segmentation scheme based on differences in effective atomic numbers was developed.MC dose calculations in a cylindrical mouse phantom with small cylindrical inhomogeneities consisting of 34 ICRU-44 tissues were performed using the EGSnrc/BEAMnrc and DOSXYZnrc codes. The dose to tissue was calculated for five different kilovoltage beams currently used in small animal radiotherapy: a microCT 120 kV beam, two 225 kV beams filtered with either 4 mm of Al or 0.5 mm of Cu, a heavily filtered 320 kV beam, and a 192Ir beam. The mean doses to the 34 ICRU-44 tissues as a function of tissue mass density and effective atomic number and beam energy were studied. A treatment plan for an orthotopic lung tumor model was created, and the dose distribution was calculated for three tissue segmentation schemes using 4, 8, and 39 tissue bins to assess the significance of the simulation results for kilovoltage radiotherapy.In our model, incorrect assignment of adipose tissue to muscle caused dose calculation differences of 27%, 13%, and 7% for the 120 kV beam and the 225 kV beams filtered with 4 mm Al and 0.5 mm Cu, respectively. For the heavily filtered 320 kV beam and a 192Ir source, potential dose calculation differences due to tissue mis-assignment were below 4%. There was no clear relationship between the dose to tissue and its mass density for x-ray beams generated by tube potentials equal or less than 225 kV. A second order polynomial fit approximated well the absorbed dose to tissue as a function of effective atomic number for these beams. In the mouse study, the 120 kV beam dose to bone was overestimated by 100% and underestimated by 10% for the 4 and 8-tissue segmentation schemes compared to the 39-tissue segmentation scheme, respectively. Dose to adipose tissue was overestimated by 30% and underestimated by 10%, respectively. In general, organ at risk (OAR) doses were overestimated in the 4-tissue and the 8-tissue segmentation schemes compared to the 39-tissue segmentation.Tissue segmentation was shown to be a key parameter for dose calculations with kilovoltage beams used in small animal radiotherapy when an x-ray tube with a potential < or = 225 kV is used as a source. A new tissue segmentation scheme with 39 tissues based on effective number differences derived from mass density differences has been implemented.
View details for DOI 10.1118/1.3589138
View details for Web of Science ID 000291405200022
View details for PubMedID 21815377
POSTRADIATION METABOLIC TUMOR VOLUME PREDICTS OUTCOME IN HEAD-AND-NECK CANCER
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2011; 80 (2): 514-521
To explore the prognostic value of metabolic tumor volume measured on postradiation (18)F-fluorodeoxyglucose positron emission tomography (PET) imaging in patients with head-and-neck cancer.Forty-seven patients with head-and-neck cancer who received pretreatment and posttreatment PET/computed tomography (CT) imaging along with definitive chemoradiotherapy were included in this study. The PET/CT parameters evaluated include the maximum standardized uptake value, metabolic tumor volume (MTV(2.0)-MTV(4.0); where MTV(2.0) refers to the volume above a standardized uptake value threshold of 2.0), and integrated tumor volume. Kaplan-Meier and Cox regression models were used to test for association between PET endpoints and disease-free survival and overall survival.Multiple postradiation PET endpoints correlated significantly with outcome; however, the most robust predictor of disease progression and death was MTV(2.0). An increase in MTV(2.0) of 21 cm(3) (difference between 75th and 25th percentiles) was associated with an increased risk of disease progression (hazard ratio [HR] = 2.5, p = 0.0001) and death (HR = 2.0, p = 0.003). In patients with nonnasopharyngeal carcinoma histology (n = 34), MTV(2.0) <18 cm(3) and MTV(2.0) ?18 cm(3) yielded 2-year disease-free survival rates of 100% and 63%, respectively (p = 0.006) and 2-year overall survival rates of 100% and 81%, respectively (p = 0.009). There was no correlation between MTV(2.0) and disease-free survival or overall survival with nasopharyngeal carcinoma histology (n = 13). On multivariate analysis, only postradiation MTV(2.0) was predictive of disease-free survival (HR = 2.47, p = 0.0001) and overall survival (HR = 1.98, p = 0.003).Postradiation metabolic tumor volume is an adverse prognostic factor in head-and-neck cancer. Biomarkers such as MTV are important for risk stratification and will be valuable in the future with risk-adapted therapies.
View details for DOI 10.1016/j.ijrobp.2010.01.057
View details for Web of Science ID 000290837100028
View details for PubMedID 20646870
Tumor Volume as a Potential Imaging-Based Risk-Stratification Factor in Trimodality Therapy for Locally Advanced Non-small Cell Lung Cancer
JOURNAL OF THORACIC ONCOLOGY
2011; 6 (5): 920-926
The role of trimodality therapy for locally advanced non-small cell lung cancer (NSCLC) continues to be defined. We hypothesized that imaging parameters on pre- and postradiation positron emission tomography (PET)-computed tomography (CT) imaging are prognostic for outcome after preoperative chemoradiotherapy (CRT)/resection/consolidation chemotherapy and could help risk-stratify patients in clinical trials.We enrolled 13 patients on a prospective clinical trial of trimodality therapy for resectable locally advanced NSCLC. PET-CT was acquired for radiation planning and after 45 Gy. Gross tumor volume (GTV) and standardized uptake value were measured at pre- and post-CRT time points and correlated with nodal pathologic complete response, loco-regional and/or distant progression, and overall survival. In addition, we evaluated the performance of automatic deformable image registration (ADIR) software for volumetric response assessment.All patients responded with average total GTV reductions after 45 Gy of 43% (range: 27-64%). Pre- and post-CRT GTVs were highly correlated (R² = 0.9), and their respective median values divided the patients into the same two groups. ADIR measurements agreed closely with manually segmented post-CRT GTVs. Patients with GTV ? median (137 ml pre-CRT and 67 ml post-CRT) had 3-year progression-free survival (PFS) of 14% versus 75% for GTV less than median, a significant difference (p = 0.049). Pre- and post-CRT PET-standardized uptake value did not correlate significantly with pathologic complete response, PFS, or overall survival.Preoperative CRT with carboplatin/docetaxel/45 Gy resulted in excellent response rates. In this exploratory analysis, pre- and post-CRT GTV predicted PFS in trimodality therapy, consistent with our earlier studies in a broader cohort of NSCLC. ADIR seems robust enough for volumetric response assessment in clinical trials.
View details for DOI 10.1097/JTO.0b013e31821517db
View details for Web of Science ID 000289554100012
View details for PubMedID 21774104
PET imaging of cerebral ischemia-induced neuroinflammation in mice using F-18-PBR06
WILEY-BLACKWELL. 2011: S319-S319
View details for Web of Science ID 000295901600319
Changes in FDG-PET/CT Parameters on Serial Pre-radiotherapy Scans Predict Disease Progression and Survival in Patients with Non-small Cell Lung Cancer
ELSEVIER SCIENCE INC. 2011: S579-S580
View details for Web of Science ID 000296411701268
(18)FLUORODEOXYGLUCOSE PET IS PROGNOSTIC OF PROGRESSION-FREE AND OVERALL SURVIVAL IN LOCALLY ADVANCED PANCREAS CANCER TREATED WITH STEREOTACTIC RADIOTHERAPY
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2010; 77 (5): 1420-1425
This study analyzed the prognostic value of positron emission tomography (PET) for locally advanced pancreas cancer patients undergoing stereotactic body radiotherapy (SBRT).Fifty-five previously untreated, unresectable pancreas cancer patients received a single fraction of 25-Gy SBRT sequentially with gemcitabine-based chemotherapy. On the preradiation PET-CT, the tumor was contoured and the maximum standardized uptake value (SUVmax) and metabolic tumor burden (MTB) were calculated using an in-house software application. High-SUVmax and low-SUVmax subgroups were created by categorizing patients above or below the median SUVmax. The analysis was repeated to form high-MTB and low-MTB subgroups as well as clinically relevant subgroups with SUVmax values of <5, 5-10, or >10. Multivariate analysis analyzing SUVmax, MTB, age, chemotherapy cycles, and pretreatment carbohydrate antigen (CA)19-9 was performed.For the entire population, median survival was 12.7 months. Median survival was 9.8 vs.15.3 months for the high- and low- SUVmax subgroups (p <0.01). Similarly, median survival was 10.1 vs. 18.0 months for the high MTB and low MTB subgroups (p <0.01). When clinical SUVmax cutoffs were used, median survival was 6.4 months in those with SUVmax >10, 9.5 months with SUVmax 5.0-10.0, and 17.7 months in those with SUVmax <5 (p <0.01). On multivariate analysis, clinical SUVmax was an independent predictor for overall survival (p = 0.03) and progression-free survival (p = 0.03).PET scan parameters can predict for length of survival in locally advanced pancreas cancer patients.
View details for DOI 10.1016/j.ijrobp.2009.06.049
View details for Web of Science ID 000280459700020
View details for PubMedID 20056345
The Tumor Microenvironment in Non-Small-Cell Lung Cancer
SEMINARS IN RADIATION ONCOLOGY
2010; 20 (3): 156-163
The tumor microenvironment (TME) of NSCLC is heterogeneous with variable blood flow through leaky immature vessels resulting in regions of acidosis and hypoxia. Hypoxia has been documented in NSCLC directly by polarographic needle electrodes and indirectly by assessing tissue and plasma hypoxia markers. In general, elevated expression of these markers portends poorer outcomes in NSCLC. Impaired vascularity and hypoxia can lead to increased metastasis and treatment resistance. Compounds that directly target hypoxic cells such as tirapazamine have been tested in clinical trials for NSCLC with mixed results. Preclinical data, however, suggest other ways of exploiting the abnormal TME in NSCLC for therapeutic gain. The inhibition of hypoxia-inducible factor-1alpha or vascular endothelial growth factor may increase local control after radiation. Inhibitors of the epidermal growth factor receptor (EGFR)/phosphatidylinositol 3-kinase (PI3K)/Akt pathway, such as erlotinib or PI-103, may "normalize" tumor vessels, allowing for increased chemotherapy delivery or improved oxygenation and radiation response. To select patients who may respond to these therapies and to evaluate the effects of these agents, a noninvasive means of imaging the TME is critical. Presently, there are several promising modalities to image hypoxia and the tumor vasculature; these include dynamic perfusion imaging and positron emission tomography scanning with radiolabled nitroimidazoles.
View details for DOI 10.1016/j.semradonc.2010.01.003
View details for Web of Science ID 000279360800003
View details for PubMedID 20685578
Investigation of the effects of treatment planning variables in small animal radiotherapy dose distributions
2010; 37 (2): 590-599
Methods used for small animal radiation treatment have yet to achieve the same dose targeting as in clinical radiation therapy. Toward understanding how to better plan small animal radiation using a system recently developed for this purpose, the authors characterized dose distributions produced from conformal radiotherapy of small animals in a microCT scanner equipped with a variable-aperture collimator.Dose distributions delivered to a cylindrical solid water phantom were simulated using a Monte Carlo algorithm. Phase-space files for 120 kVp x-ray beams and collimator widths of 1-10 mm at isocenter were generated using BEAMnrc software, and dose distributions for evenly spaced beams numbered from 5 to 80 were generated in DOSXYZnrc for a variety of targets, including centered spherical targets in a range of sizes, spherical targets offset from centered by various distances, and various ellipsoidal targets. Dose distributions were analyzed using dose volume histograms. The dose delivered to a mouse bearing a spontaneous lung tumor was also simulated, and dose volume histograms were generated for the tumor, heart, left lung, right lung, and spinal cord.Results indicated that for centered, symmetric targets, the number of beams required to achieve a smooth dose volume histogram decreased with increased target size. Dose distributions for noncentered, symmetric targets did not exhibit any significant loss of conformality with increasing offset from the phantom center, indicating sufficient beam penetration through the phantom for targeting superficial targets from all angles. Even with variable collimator widths, targeting of asymmetric targets was found to have less conformality than that of spherical targets. Irradiation of a mouse lung tumor with multiple beam widths was found to effectively deliver dose to the tumor volume while minimizing dose to other critical structures.Overall, this method of generating and analyzing dose distributions provides a quantitative method for developing practical guidelines for small animal radiotherapy treatment planning. Future work should address methods to improve conformality in asymmetric targets.
View details for DOI 10.1118/1.3276738
View details for Web of Science ID 000274075600019
View details for PubMedID 20229867
Prognostic Value of Metabolic Tumor Volume and Velocity in Predicting Head and Neck Cancer Outcomes
ELSEVIER SCIENCE INC. 2010: S460-S460
View details for Web of Science ID 000288775701074
Mid-treatment Metabolic Tumor Volume Predicts Progression and Death among Patients with Hodgkin's Disease
ELSEVIER SCIENCE INC. 2010: S546-S547
View details for Web of Science ID 000288775701265
Pharmacologically Increased Tumor Hypoxia Can Be Measured by F-18-Fluoroazomycin Arabinoside Positron Emission Tomography and Enhances Tumor Response to Hypoxic Cytotoxin PR-104
CLINICAL CANCER RESEARCH
2009; 15 (23): 7170-7174
Solid tumors contain microenvironmental regions of hypoxia that present a barrier to traditional radiotherapy and chemotherapy, and this work describes a novel approach to circumvent hypoxia. We propose to overcome hypoxia by augmenting the effectiveness of drugs that are designed to specifically kill hypoxic tumor cells.We have constructed RKO colorectal tumor cells that express a small RNA hairpin that specifically knocks down the hypoxia-inducible factor 1a (HIF1a) transcription factor. We have used these cells in vitro to determine the effect of HIF1 on cellular sensitivity to the hypoxic cytotoxin PR-104, and its role in cellular oxygen consumption in response to the pyruvate dehydrogenase kinase inhibitor dichloroacetate (DCA). We have further used these cells in vivo in xenografted tumors to determine the role of HIF1 in regulating tumor hypoxia in response to DCA using (18)F-fluoroazomycin arabinoside positron emission tomography, and its role in regulating tumor sensitivity to the combination of DCA and PR-104.HIF1 does not affect cellular sensitivity to PR-104 in vitro. DCA transiently increases cellular oxygen consumption in vitro and increases the extent of tumor hypoxia in vivo as measured with (18)F-fluoroazomycin arabinoside positron emission tomography. Furthermore, we show that DCA-dependent alterations in hypoxia increase the antitumor activity of the next-generation hypoxic cytotoxin PR-104.DCA interferes with the HIF-dependent "adaptive response," which limits mitochondrial oxygen consumption. This approach transiently increases tumor hypoxia and represents an important method to improve antitumor efficacy of hypoxia-targeted agents, without increasing toxicity to oxygenated normal tissue.
View details for DOI 10.1158/1078-0432.CCR-09-1676
View details for Web of Science ID 000272363700011
View details for PubMedID 19920111
Kilovoltage beam Monte Carlo dose calculations in submillimeter voxels for small animal radiotherapy
2009; 36 (11): 4991-4999
Small animal conformal radiotherapy (RT) is essential for preclinical cancer research studies and therefore various microRT systems have been recently designed. The aim of this paper is to efficiently calculate the dose delivered using our microRT system based on a microCT scanner with the Monte Carlo (MC) method and to compare the MC calculations to film measurements.Doses from 2-30 mm diameter 120 kVp photon beams deposited in a solid water phantom with 0.2 x 0.2 x 0.2 mm3 voxels are calculated using the latest versions of the EGSnrc codes BEAMNRC and DOSXYZNRC. Two dose calculation approaches are studied: a two-step approach using phase-space files and direct dose calculation with BEAMNRC simulation sources. Due to the small beam size and submillimeter voxel size resulting in long calculation times, variance reduction techniques are studied. The optimum bremsstrahlung splitting number (NBRSPL in BEAMNRC) and the optimum DOSXYZNRC photon splitting (Nsplit) number are examined for both calculation approaches and various beam sizes. The dose calculation efficiencies and the required number of histories to achieve 1% statistical uncertainty--with no particle recycling--are evaluated for 2-30 mm beams. As a final step, film dose measurements are compared to MC calculated dose distributions.The optimum NBRSPL is approximately 1 x 10(6) for both dose calculation approaches. For the dose calculations with phase-space files, Nsplit varies only slightly for 2-30 mm beams and is established to be 300. Nsplit for the DOSXYZNRC calculation with the BEAMNRC source ranges from 300 for the 30 mm beam to 4000 for the 2 mm beam. The calculation time significantly increases for small beam sizes when the BEAMNRC simulation source is used compared to the simulations with phase-space files. For the 2 and 30 mm beams, the dose calculations with phase-space files are more efficient than the dose calculations with BEAMNRC sources by factors of 54 and 1.6, respectively. The dose calculation efficiencies converge for beams with diameters larger than 30 mm.A very good agreement of MC calculated dose distributions to film measurements is found. The mean difference of percentage depth dose curves between calculated and measured data for 2, 5, 10, and 20 mm beams is 1.8%.
View details for DOI 10.1118/1.3238465
View details for Web of Science ID 000271217900018
View details for PubMedID 19994508
Quantification of pre-treatment metabolic tumor growth rate in lung cancer
LIPPINCOTT WILLIAMS & WILKINS. 2009: S733-S733
View details for Web of Science ID 000269496002262
Mid-treatment PET predicts progression in hypofractionated accelerated radiation therapy for lung tumors
LIPPINCOTT WILLIAMS & WILKINS. 2009: S939-S939
View details for Web of Science ID 000269496002721
Pancreatic Tumor Motion on a Single Planning 4D-CT Does Not Correlate With Intrafraction Tumor Motion During Treatment
AMERICAN JOURNAL OF CLINICAL ONCOLOGY-CANCER CLINICAL TRIALS
2009; 32 (4): 364-368
To quantify pancreas tumor motion on both a planning 4D-CT and during a single fraction treatment using the CyberKnife linear accelerator and Synchrony respiratory tracking software, and to investigate whether a single 4D-CT study is reliable for determining radiation treatment margins for patients with locally advanced pancreas cancer.Twenty patients underwent fiducial placement, biphasic pancreatic protocol CT scan and 4D-CT scan in the treatment position while free-breathing. Patients were then treated with a single 25 Gy fraction of stereotactic body radiotherapy. Predicted pancreas motion in the superior-inferior (SI), left-right (LR), and anterior-posterior (AP) directions was calculated from the maximum inspiration and maximum expiration 4D-CT scan. For CyberKnife treatments, mean respiratory cycle motion and maximum respiratory cycle motion was determined in the SI, LR, and AP directions.The range of centroid movement based on 4D-CT in the SI, LR, and AP directions were 0.9 to 28.8 mm, 0.1 to 13.7 mm, and 0.2 to 7.6 mm, respectively. During CyberKnife treatment, in the SI direction, the mean motion of the centroid ranged from 0.5 to 12.7 mm. In the LR direction, the mean motion range was 0.4 to 9.4 mm. In the AP direction, the mean motion range was 0.6 to 5.5 mm. The maximum range of movement (mean) during CyberKnife treatment in the SI, LR, and AP directions were 4.5 to 48.8 mm (mean 20.8 mm), 1.5 to 41.3 mm (mean 11.3 mm), and 1.6 to 68.1 mm (mean 13.4 mm), respectively. Neither the maximum or mean motion correlated with the 4D-CT movement.There is substantial respiratory associated motion of pancreatic tumors. The 4D-CT planning scans cannot accurately predict the movement of pancreatic tumors during actual treatment on CyberKnife.
View details for DOI 10.1097/COC.0b013e31818da9e0
View details for Web of Science ID 000268761600007
View details for PubMedID 19398901
METABOLIC TUMOR VOLUME PREDICTS FOR RECURRENCE AND DEATH IN HEAD-AND-NECK CANCER
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2009; 74 (5): 1335-1341
To evaluate the prognostic value of metabolic tumor volume measured on 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) imaging and other clinical factors in patients treated for locally advanced head-and-neck cancer (HNC) at a single institution.Between March 2003 and August 2007, 85 patients received positron emission tomography (PET)/computed tomography-guided chemoradiotherapy for HNC. Metabolically active tumor regions were delineated on pretreatment PET scans semiautomatically using custom software. We evaluated the relationship of (18)F-fluorodeoxyglucose-PET maximum standardized uptake value (SUV) and total metabolic tumor volume (MTV) with disease-free survival (DFS) and overall survival (OS).Mean follow-up for surviving patients was 20.4 months. The estimated 2-year locoregional control, DFS, and OS for the group were 88.0%, 69.5%, and 78.4%, respectively. The median time to first failure was 9.8 months among the 16 patients with relapse. An increase in MTV of 17.4 mL (difference between the 75th and 25th percentiles) was significantly associated with an increased hazard of first event (recurrence or death) (1.9-fold, p < 0.001), even after controlling for Karnofsky performance status (KPS) (1.8-fold, p = 0.001), and of death (2.1-fold, p < 0.001). We did not find a significant relationship of maximum SUV, stage, or other clinical factors with DFS or OS.Metabolic tumor volume is an adverse prognostic factor for disease recurrence and death in HNC. MTV retained significance after controlling for KPS, the only other significant adverse prognostic factor found in this cohort. MTV is a direct measure of tumor burden and is a potentially valuable tool for risk stratification and guiding treatment in future studies.
View details for DOI 10.1016/j.ijrobp.2008.10.060
View details for Web of Science ID 000268346100006
View details for PubMedID 19289263
Commissioning of a novel microCT/RT system for small animal conformal radiotherapy
PHYSICS IN MEDICINE AND BIOLOGY
2009; 54 (12): 3727-3740
The purpose of this work was to commission a 120 kVp photon beam produced by a micro-computed tomography (microCT) scanner for use in irradiating mice to therapeutic doses. A variable-aperture collimator has been integrated with a microCT scanner to allow the delivery of beams with pseudocircular profiles of arbitrary width between 0.1 and 6.0 cm. The dose rate at the isocenter of the system was measured using ion chamber and gafchromic EBT film as 1.56-2.13 Gy min(-1) at the water surface for field diameters between 0.2 and 6.0 cm. The dose rate decreases approximately 10% per every 5 mm depth in water for field diameters between 0.5 and 1.0 cm. The flatness, symmetry and penumbra of the beam are 3.6%, 1.0% and 0.5 mm, respectively. These parameters are sufficient to accurately conform the radiation dose delivered to target organs on mice. The irradiated field size is affected principally by the divergence of the beam. In general, the beam has appropriate dosimetric characteristics to accurately deliver the dose to organs inside the mice's bodies. Using multiple beams delivered from a variety of angular directions, targets as small as 2 mm may be irradiated while sparing surrounding tissue. This microCT/RT system is a feasible tool to irradiate mice using treatment planning and delivery methods analogous to those applied to humans.
View details for DOI 10.1088/0031-9155/54/12/008
View details for Web of Science ID 000266582300008
View details for PubMedID 19478377
A bone composition model for Monte Carlo x-ray transport simulations
2009; 36 (3): 1008-1018
In the megavoltage energy range although the mass attenuation coefficients of different bones do not vary by more than 10%, it has been estimated that a simple tissue model containing a single-bone composition could cause errors of up to 10% in the calculated dose distribution. In the kilovoltage energy range, the variation in mass attenuation coefficients of the bones is several times greater, and the expected error from applying this type of model could be as high as several hundred percent. Based on the observation that the calcium and phosphorus compositions of bones are strongly correlated with the bone density, the authors propose an analytical formulation of bone composition for Monte Carlo computations. Elemental compositions and densities of homogeneous adult human bones from the literature were used as references, from which the calcium and phosphorus compositions were fitted as polynomial functions of bone density and assigned to model bones together with the averaged compositions of other elements. To test this model using the Monte Carlo package DOSXYZnrc, a series of discrete model bones was generated from this formula and the radiation-tissue interaction cross-section data were calculated. The total energy released per unit mass of primary photons (terma) and Monte Carlo calculations performed using this model and the single-bone model were compared, which demonstrated that at kilovoltage energies the discrepancy could be more than 100% in bony dose and 30% in soft tissue dose. Percentage terma computed with the model agrees with that calculated on the published compositions to within 2.2% for kV spectra and 1.5% for MV spectra studied. This new bone model for Monte Carlo dose calculation may be of particular importance for dosimetry of kilovoltage radiation beams as well as for dosimetry of pediatric or animal subjects whose bone composition may differ substantially from that of adult human bones.
View details for DOI 10.1118/1.3077129
View details for Web of Science ID 000263718100034
View details for PubMedID 19378761
The Role of Tumor Cell-Derived Connective Tissue Growth Factor (CTGF/CCN2) in Pancreatic Tumor Growth
2009; 69 (3): 775-784
Pancreatic cancer is highly aggressive and refractory to existing therapies. Connective tissue growth factor (CTGF/CCN2) is a fibrosis-related gene that is thought to play a role in pancreatic tumor progression. However, CCN2 can be expressed in a variety of cell types, and the contribution of CCN2 derived from either tumor cells or stromal cells as it affects the growth of pancreatic tumors is unknown. Using genetic inhibition of CCN2, we have discovered that CCN2 derived from tumor cells is a critical regulator of pancreatic tumor growth. Pancreatic tumor cells derived from CCN2 shRNA-expressing clones showed dramatically reduced growth in soft agar and when implanted s.c. We also observed a role for CCN2 in the growth of pancreatic tumors implanted orthotopically, with tumor volume measurements obtained by positron emission tomography imaging. Mechanistically, CCN2 protects cells from hypoxia-mediated apoptosis, providing an in vivo selection for tumor cells that express high levels of CCN2. We found that CCN2 expression and secretion was increased in hypoxic pancreatic tumor cells in vitro, and we observed colocalization of CCN2 and hypoxia in pancreatic tumor xenografts and clinical pancreatic adenocarcinomas. Furthermore, we found increased CCN2 staining in clinical pancreatic tumor tissue relative to stromal cells surrounding the tumor, supporting our assertion that tumor cell-derived CCN2 is important for pancreatic tumor growth. Taken together, these data improve our understanding of the mechanisms responsible for pancreatic tumor growth and progression, and also indicate that CCN2 produced by tumor cells represents a viable therapeutic target for the treatment of pancreatic cancer.
View details for DOI 10.1158/0008-5472.CAN-08-0987
View details for Web of Science ID 000263048700010
View details for PubMedID 19179545
AUTOMATED RADIOSYNTHESIS OF [F-18]EF-5 FOR IMAGING HYPOXIA IN HUMAN
WILEY-BLACKWELL. 2009: S274-S274
View details for Web of Science ID 000268724900275
In vivo H-1 magnetic resonance spectroscopy of lactate in patients with Stage IV head and neck squamous cell carcinoma
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2008; 71 (4): 1151-1157
To investigate in vivo(1)H magnetic resonance spectroscopy imaging of lactate for assessing tumor hypoxia in head and neck cancers and to determine its utility in predicting the response and outcomes.Volume-localized lactate-edited (1)H magnetic resonance spectroscopy at 1.5 T was performed in vivo on involved neck nodes and control subcutaneous tissues in 36 patients with Stage IV head and neck cancer. The signal intensities (SIs) of lactate, choline, and creatine and the choline/creatine ratio were measured. The tumor partial pressure of oxygen (pO(2)) was obtained in the same lymph node before MRS. Patients were treated with either two cycles of induction chemotherapy (tirapazamine, cisplatin, 5-fluorouracil) followed by simultaneous chemoradiotherapy or the same regimen without tirapazamine. The lactate SI and the choline/creatine ratio correlated with the tumor pO(2), nodal response, and locoregional control.The lactate SI was greater for the involved nodes (median, 0.25) than for the subcutaneous tissue (median, 0.04; p = 0.07). No significant correlation was found between the lactate SI and tumor pO(2) (mean, 0.46 +/- 0.10 for hypoxic nodes [pO(2) < or =10 mm Hg, n = 15] vs. 0.36 +/- 0.07 for nonhypoxic nodes [pO(2) >10 mm Hg, n = 21], p = 0.44). A significant correlation was found between the choline/creatine ratios and tumor pO(2) (mean, 2.74 +/- 0.34 for hypoxic nodes vs. 1.78 +/- 0.31 for nonhypoxic nodes, p = 0.02). No correlation was found between the lactate SI and the complete nodal response (p = 0.52) or locoregional control rates.The lactate SI did not correlate with tumor pO(2), treatment response, or locoregional control. Additional research is needed to refine this technique.
View details for DOI 10.1016/j.ijrobp.2007.11.030
View details for Web of Science ID 000257299200025
View details for PubMedID 18258377
Metabolic tumor volume predicts for recurrence and death in head and neck cancer
ELSEVIER SCIENCE INC. 2008: S159-S160
View details for Web of Science ID 000258805300356
Design and evaluation of a variable aperture collimator for conformal radiotherapy of small animals using a microCT scanner
2007; 34 (11): 4359-4367
Treatment of small animals with radiation has in general been limited to planar fields shaped with lead blocks, complicating spatial localization of dose and treatment of deep-seated targets. In order to advance laboratory radiotherapy toward what is accomplished in the clinic, we have constructed a variable aperture collimator for use in shaping the beam of microCT scanner. This unit can image small animal subjects at high resolution, and is capable of delivering therapeutic doses in reasonable exposure times. The proposed collimator consists of two stages, each containing six trapezoidal brass blocks that move along a frame in a manner similar to a camera iris producing a hexagonal aperture of variable size. The two stages are offset by 30 degrees and adjusted for the divergence of the x-ray beam so as to produce a dodecagonal profile at isocenter. Slotted rotating driving plates are used to apply force to pins in the collimator blocks and effect collimator motion. This device has been investigated through both simulation and measurement. The collimator aperture size varied from 0 to 8.5 cm as the driving plate angle increased from 0 to 41 degrees. The torque required to adjust the collimator varied from 0.5 to 5 N x m, increasing with increasing driving plate angle. The transmission profiles produced by the scanner at isocenter exhibited a penumbra of approximately 10% of the collimator aperture width. Misalignment between the collimator assembly and the x-ray source could be identified on the transmission images and corrected by adjustment of the collimator location. This variable aperture collimator technology is therefore a feasible and flexible solution for adjustable shaping of radiation beams for use in small animal radiotherapy as well as other applications in which beam shaping is desired.
View details for DOI 10.1118/1.2789498
View details for Web of Science ID 000251145900029
View details for PubMedID 18072501
Metabolic tumor burden predicts for disease progression and death in lung cancer
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2007; 69 (2): 328-333
In lung cancer, stage is an important prognostic factor for disease progression and survival. However, stage may be simply a surrogate for underlying tumor burden. Our purpose was to assess the prognostic value of tumor burden measured by 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging.We identified 19 patients with lung cancer who had staging PET-CT scans before any therapy, and adequate follow-up (complete to time of progression for 18, and death for 15 of 19). Metabolically active tumor regions were segmented on pretreatment PET scans semi-automatically using custom software. We determined the relationship between times to progression (TTP) and death (OS) and two PET parameters: total metabolic tumor volume (MTV), and standardized uptake value (SUV).The estimated median TTP and OS for the cohort were 9.3 months and 14.8 months. On multivariate Cox proportional hazards regression analysis, an increase in MTV of 25 ml (difference between the 75th and 25th percentiles) was associated with increased hazard of progression and of death (5.4-fold and 7.6-fold), statistically significant (p = 0.0014 and p = 0.001) after controlling for stage, treatment intent (definitive or palliative), age, Karnofsky performance status, and weight loss. We did not find a significant relationship between SUV and TTP or OS.In this study, high tumor burden assessed by PET MTV is an independent poor prognostic feature in lung cancer, promising for stratifying patients in randomized trials and ultimately for selecting risk-adapted therapies. These results will need to be validated in larger cohorts with longer follow-up, and evaluated prospectively.
View details for DOI 10.1016/j.ijrobp.2007.04.036
View details for Web of Science ID 000249796100002
View details for PubMedID 17869659
Oxygen sensitivity of reporter genes: Implications for preclinical imaging of tumor hypoxia
2007; 6 (4): 219-228
Reporter gene techniques have been applied toward studying the physiologic phenomena associated with tumor hypoxia, a negative prognostic indicator. The purpose of this study was to assess the potential adverse effects of hypoxic conditions on the effectiveness of four commonly used reporter genes: Renilla luciferase, monomeric red fluorescent protein, thymidine kinase, and lacZ. Tumor-forming A375 cells expressing a trifusion reporter consisting of Renilla luciferase, monomeric red fluorescent protein, and thymidine kinase were subjected to decreasing oxygen tensions and assayed for reporter expression and activity. A375 cells expressing beta-galactosidase were similarly exposed to hypoxia, with activity of the reporter monitored by cleavage of the fluorescent substrate 7-hydroxy-9H-(1,3-dichloro-9,9-dimethylacridin-2-one)-beta-galactoside (DDAOG). Generation of signal in in vivo tumor models expressing bioluminescent or beta-galactosidase reporters were also examined over the course of hypoxic stresses, either by tumor clamping or the antivascular agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA). Our findings indicate that bioluminescent and fluorescent reporter activity are decreased under hypoxia despite minimal variations in protein production, whereas beta-galactosidase reporter activity per unit protein was unchanged. These results demonstrate that combining beta-galactosidase with the DDAOG optical probe may be a robust reporter system for the in vivo study of tumor hypoxia.
View details for DOI 10.2310/7290.2007.00017
View details for Web of Science ID 000249349100001
View details for PubMedID 17711777
Small-animal PET of melanocortin 1 receptor expression using a F-18-labeled alpha-melanocyte-stimulating hormone analog
JOURNAL OF NUCLEAR MEDICINE
2007; 48 (6): 987-994
(18)F-Labeled small synthetic peptides have emerged as attractive probes for imaging various molecular targets with PET. The alpha-melanocyte-stimulating hormone (alpha-MSH) receptor (melanocortin type 1 receptor [MC1R]) is overexpressed in most murine and human melanomas. It is a promising molecular target for diagnosis and therapy of melanomas. However, (18)F compounds have not been successfully developed for imaging the MC1R.In this study, an alpha-MSH analog, Ac-Nle-Asp-His-D-Phe-Arg-Trp-Gly-Lys-NH(2) (NAPamide), was radiolabeled with N-succinimidyl-4-(18)F-fluorobenzoate ((18)F-SFB). The resulting radiopeptide was evaluated as a potential molecular probe for small-animal PET of melanoma and MC1R expression in melanoma xenografted mouse models.The binding affinity of (19)F-SFB-conjugated NAPamide, (19)F-FB-NAPamide, was determined to be 7.2 +/- 1.2 nM (mean +/- SD) using B16/F10 cells and (125)I-(Tyr(2))-[Nle(4),D-Phe(7)]-alpha-MSH [(125)I-(Tyr(2))-NDP] as a radioligand. The biodistribution of (18)F-FB-NAPamide was then investigated in C57BL/6 mice bearing subcutaneous murine B16/F10 melanoma tumors with high expression of MC1Rs and Fox Chase Scid mice bearing human A375M melanoma with a relatively low number of MC1R receptors. Biodistribution experiments showed that tumor uptake values (percentage injected dose per gram of tumor [%ID/g]) of (18)F-FB-NAPamide were 1.19 +/- 0.11 %ID/g and 0.46 +/- 0.11 %ID/g, in B16/F10 and A375M xenografted melanoma at 1 h after injection, respectively. Furthermore, the B16/F10 tumor uptake was significantly inhibited by coinjection with excess alpha-MSH peptide (P < 0.05), indicating that (18)F-FB-NAPamide specifically recognizes the MC1R in living mice. Small-animal PET of (18)F-FB-NAPamide in mice bearing B16/F10 and A375M tumors at 1 h after tail vein injection revealed good B16/F10 tumor-to-background contrast and low A375M tumor-to-background ratios.(18)F-FB-NAPamide is a promising molecular probe for alpha-MSH receptor-positive melanoma PET and warrants further study.
View details for DOI 10.2967/jnumed.107.039602
View details for Web of Science ID 000247054800024
View details for PubMedID 17504880
Imaging tumoral hypoxia: Oxygen concentrations and beyond
2007; 21 (3): 368-376
The role of hypoxia as a key determinant of outcome for human cancers has encouraged efforts to noninvasively detect and localize regions of poor oxygenation in tumors. In this review, we will summarize existing and developing techniques for imaging tumoral hypoxia. A brief review of the biology of tumor oxygenation and its effect on tumor cells will be provided initially. We will then describe existing methods for measurement of tissue oxygenation status. An overview of emerging molecular imaging techniques based on radiolabeled hypoxic markers such as misonidazole or hypoxia-related genes and proteins will then be given, and the usefulness of these approaches toward targeting hypoxia directly will be assessed. Finally, we will evaluate the clinical potential of oxygen- and molecular-specific techniques for imaging hypoxia, and discuss how these methods will individually and collectively advance oncology.
View details for Web of Science ID 000253822400010
View details for PubMedID 17447439
Lactate-base H-1 magnetic spectroscopy does not predict response and outcomes in patients with stage IV head and neck squamous cell carcinoma
ELSEVIER SCIENCE INC. 2007: S200-S201
View details for Web of Science ID 000249950200352
Perfusion, diffusion and spectroscopy values in newly diagnosed cerebral gliomas
NMR IN BIOMEDICINE
2006; 19 (4): 463-475
To evaluate perfusion, diffusion, and spectroscopy values in enhancing and non-enhancing lesions for patients with newly diagnosed gliomas of different grades.Sixty-seven patients with newly diagnosed glioma were entered into the study 20 grade II, 26 grade III and 21 grade IV. MR data were acquired at 1.5T and included diffusion weighted images (59/67 patients), dynamic perfusion weighted images (30/67 patients) and 3D H-1 MR spectroscopy (64/67 patients). Enhancing and non-enhancing lesions were delineated by a neuroradiologist and applied to maps of relative cerebral blood volume (rCBV), apparent diffusion coefficient (ADC), relative anisotropy (RA) and metabolite intensities.The median rCBV within enhancing regions of grade IV gliomas was significantly elevated relative to enhancing regions in grade III gliomas and normal brain. ADC was elevated relative to normal brain, but was not significantly different between grades or between enhancing and non-enhancing regions. The RA was higher in the non-enhancing region of grade IV gliomas relative to grade II and grade III. Levels of lactate plus lipid were significantly elevated in grade IV relative to grade II and grade III gliomas. Both enhancing and non-enhancing regions in grade IV gliomas showed significant correlations between CBV, ADC and choline levels.The data were consistent with grade IV gliomas having higher membrane turnover, increased cell density and increased vascularity within enhancing lesions. Analysis of the correlations among parameters within grade IV gliomas suggested that high vascularity (high rCBV) was correlated with increased cellularity (low ADC) and increased membrane turnover (high choline) in these lesions. The non-enhancing region of grades II and III gliomas had MR parameters consistent with increased cellularity and/or membrane turnover.
View details for DOI 10.1002/nbm.1059
View details for Web of Science ID 000238883100004
View details for PubMedID 16763973
Validation of in vivo fluorochrome concentrations measured using fluorescence molecular tomography
JOURNAL OF BIOMEDICAL OPTICS
2005; 10 (4)
Fluorescence molecular tomography (FMT) has emerged as a means of quantitatively imaging fluorescent molecular probes in three dimensions in living systems. To assess the accuracy of FMT in vivo, translucent plastic tubes containing a turbid solution with a known concentration of Cy 5.5 fluorescent dye are constructed and implanted subcutaneously in nude mice, simulating the presence of a tumor accumulating a fluorescent molecular reporter. Comparisons between measurements of fluorescent tubes made before and after implantation demonstrate that the accuracy of FMT reported for homogeneous phantoms extends to the in vivo situation. The sensitivity of FMT to background fluorescence is tested by imaging fluorescent tubes in mice injected with Cy 5.5-labeled Annexin V. For small tube fluorochrome concentrations, the presence of background fluorescence results in increases in the reconstructed concentration. This phenomenon is counteracted by applying a simple subtraction correction to the measured fluorescence data. The effects of varying tumor photon absorption are simulated by imaging fluorescent tubes with varying ink concentrations, and are found to be minor. These findings demonstrate the in vivo quantitative accuracy of fluorescence tomography, and encourage further development of this imaging modality as well as application of FMT in molecular imaging studies using fluorescent reporters.
View details for DOI 10.1117/1.1993427
View details for Web of Science ID 000232799200028
View details for PubMedID 16178652
Relationship of MR-derived lactate, mobile lipids, and relative blood volume for gliomas in vivo
AMERICAN JOURNAL OF NEURORADIOLOGY
2005; 26 (4): 760-769
Gliomas are heterogeneous tumors with increased microvasculature, hypoxia, and necrosis. The purpose of this study was to examine the distribution and relationship of the MR-derived relative cerebral blood volume (rCBV), lactate (Lac), and mobile lipids (Lip), which have been proposed as markers for these phenomena of gliomas in vivo.Twenty-three patients with newly diagnosed gliomas were examined before surgical biopsy and/or resection (seven grade II, five grade III, and 11 grade IV), and 27 patients were studied after surgery but before radiation treatment and/or chemotherapy (11 grade II, two grade III, and 14 grade IV gliomas). Lac and Lip were estimated from Lac-edited three-dimensional MR spectroscopic images. Dynamic susceptibility-contrast MR imaging was applied to obtain perfusion-weighted images and rCBV maps.Before surgical biopsy/resection, one low-grade and 12 of 16 high-grade gliomas had significantly elevated Lac. No low-grade and 10 of 16 high-grade gliomas had significantly elevated Lip. In presurgical high-grade gliomas, volumes of elevated Lip and macronecrosis were significantly correlated. rCBV was significantly increased in regions with elevated Lac. After we excluded macronecrosis, the rCBV for regions with elevated Lip but no Lac was significantly higher than rCBV in regions with elevated Lac but no Lip. After surgical biopsy/resection, more low-grade patients showed significantly elevated Lac and Lip than before.The in vivo distribution of rCBV, Lac, and Lip, as evaluated with three-dimensional MR spectroscopic imaging, may help in the diagnosis and selection of the most appropriate therapy for patients with gliomas.
View details for Web of Science ID 000228273400017
View details for PubMedID 15814918
Effect of respiratory cycle irregularities on image quality in four-dimensional computed tomography
ELSEVIER SCIENCE INC. 2005: S506-S506
View details for Web of Science ID 000232083301373
Visualization of antitumor treatment by means of fluorescence molecular tomography with an annexin V-Cy5.5 conjugate
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2004; 101 (33): 12294-12299
In vivo imaging of treatment responses at the molecular level could have a significant impact on the speed of drug discovery and ultimately lead to personalized medicine. Strong interest has been shown in developing quantitative fluorescence-based technologies with good molecular specificity and sensitivity for noninvasive 3D imaging through tissues and whole animals. We show herein that tumor response to chemotherapy can be accurately resolved by fluorescence molecular tomography (FMT) with a phosphatidylserine-sensing fluorescent probe based on modified annexins. We observed at least a 10-fold increase of fluorochrome concentration in cyclophosphamide-sensitive tumors and a 7-fold increase of resistant tumors compared with control studies. FMT is an optical imaging technique developed to overcome limitations of commonly used planar illumination methods and demonstrates higher quantification accuracy validated by histology. It is further shown that a 3-fold variation in background absorption heterogeneity may yield 100% errors in planar imaging but only 20% error in FMT, thus confirming tomographic imaging as a preferred tool for quantitative investigations of fluorescent probes in tissues. Tomographic approaches are found essential for small-animal optical imaging and are potentially well suited for clinical drug development and monitoring.
View details for DOI 10.1073/pnas.0401137101
View details for Web of Science ID 000223410100070
View details for PubMedID 15304657
Fluorescence molecular imaging of small animal tumor models
CURRENT MOLECULAR MEDICINE
2004; 4 (4): 419-430
In vivo imaging of molecular events in small animals has great potential to impact basic science and drug development. For this reason, several imaging technologies have been adapted to small animal research, including X-ray, magnetic resonance, and radioisotope imaging. Despite this plethora of visualization techniques, fluorescence imaging is emerging as an important alternative because of its operational simplicity, safety, and cost-effectiveness. Fluorescence imaging has recently become particularly interesting because of advances in fluorescent probe technology, including targeted fluorochromes as well as fluorescent "switches" sensitive to specific biochemical events. While past biological investigations using fluorescence have focused on microscopic examination of ex vivo, in vitro, or intravital specimens, techniques for macroscopic fluorescence imaging are now emerging for in vivo molecular imaging applications. This review illuminates fluorescence imaging technologies that hold promise for small animal imaging. In particular we focus on planar illumination techniques, also known as Fluorescence Reflectance Imaging (FRI), and discuss its performance and current use. We then discuss fluorescence molecular tomography (FMT), an evolving technique for quantitative three-dimensional imaging of fluorescence in vivo. This technique offers the promise of non-invasively quantifying and visualizing specific molecular activity in living subjects in three dimensions.
View details for Web of Science ID 000221658700008
View details for PubMedID 15354872
Singular-value analysis and optimization of experimental parameters in fluorescence molecular tomography
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION
2004; 21 (2): 231-241
The advent of specific molecular markers and probes employing optical reporters has encouraged the application of in vivo diffuse tomographic imaging at greater spatial resolutions and hence data-set volumes. This study applied singular-value analysis (SVA) of the fluorescence tomographic problem to determine optimal source and detector distributions that result in data sets that are balanced between information content and size. Weight matrices describing the tomographic forward problem were constructed for a range of source and detector distributions and fields of view and were decomposed into their associated singular values. These singular-value spectra were then compared so that we could observe the effects of each parameter on imaging performance. The findings of the SVA were then confirmed by examining reconstructions of simulated and experimental data acquired with the same optode distributions as examined by SVA. It was seen that for a 20-mm target width, which is relevant to the small-animal imaging situation, the source and detector fields of view should be set at approximately 30 mm. Equal numbers of sources and detectors result in the best imaging performance in the parallel-plate geometry and should be employed when logistically feasible. These data provide guidelines for the design of small-animal diffuse optical tomographic imaging systems and demonstrate the utility of SVA as a simple and efficient means of optimizing experimental parameters in problems for which a forward model of the data collection process is available.
View details for Web of Science ID 000188183900009
View details for PubMedID 14763766
A method of target definition in PET-based radiotherapy planning
ELSEVIER SCIENCE INC. 2004: S602-S602
View details for Web of Science ID 000223854700784
Fluorescence Molecular Tomography: New detection schemes for acquiring high information content measurements
2004 2ND IEEE INTERNATIONAL SYMPOSIUM ON BIOMEDICAL IMAGING: MACRO TO NANO, VOLS 1 AND 2
View details for Web of Science ID 000227671301109
In vivo high resolution three-dimensional imaging of antigen-specific cytotoxic T-lymphocyte trafficking to tumors
2003; 63 (20): 6838-6846
Magnetic resonance imaging (MRI) allows noninvasive and three-dimensional visualization of whole organisms over time, and, therefore, would be ideally suited to monitor cell trafficking in vivo. Until now, systemically injected cells had been difficult to visualize by MRI because of relatively inefficient labeling methods. We developed a novel, biocompatible, and physiologically inert nanoparticle (highly derivatized cross-linked iron oxide nanoparticle; CLIO-HD) for highly efficient intracellular labeling of a variety of cell types that now allows in vivo MRI tracking of systemically injected cells at near single-cell resolution. CD8+ cytotoxic T lymphocytes labeled with CLIO-HD were detectable via MRI with a detection threshold of 2 cells/voxel in vitro and approximately 3 cells/voxel in vivo in live mice. Using B16-OVA melanoma and CLIO-HD-labeled OVA-specific CD8+ T cells, we have demonstrated for the first time high resolution imaging of T-cell recruitment to intact tumors in vivo. We have revealed the extensive three-dimensional spatial heterogeneity of T-cell recruitment to target tumors and demonstrated a temporal regulation of T-cell recruitment within the tumor. Significantly, our data indicate that serial administrations of CD8+ T cells appear to home to different intratumoral locations, and may, therefore, provide a more effective treatment regimen than a single bolus administration. Together, these results demonstrate that CLIO-HD is uniquely suited for quantitative repetitive MRI of adoptively transferred cells and that this approach may be particularly useful for evaluating novel cell-based therapies in vivo.
View details for Web of Science ID 000186213800035
View details for PubMedID 14583481
A submillimeter resolution fluorescence molecular imaging system for small animal imaging
2003; 30 (5): 901-911
Most current imaging systems developed for tomographic investigations of intact tissues using diffuse photons suffer from a limited number of sources and detectors. In this paper we describe the construction and evaluation of a large dataset, low noise tomographic system for fluorescence imaging in small animals. The system consists of a parallel plate-imaging chamber and a lens coupled CCD camera, which enables conventional planar imaging as well as fluorescence tomography. The planar imaging data are used to guide the acquisition of a Fluorescence Molecular Tomography (FMT) dataset containing more than 106 measurements, and to superimpose anatomical features with tomographic results for improved visual representation. Experimental measurements exhibited good agreement with the diffusion theory models used to predict light propagation within the chamber. Tests of the instrument's capacity to quantitatively reconstruct fluorochrome distributions in three dimensions showed less than 5% errors between actual fluorochrome concentrations and FMT findings, and suggested a detection threshold of approximately 100 femptomoles for small localized objects. Experiments to assess the instrument's spatial resolution demonstrated the ability of the system to resolve objects placed at clear distances of less than 1 mm. This is a significant resolution increase over previously developed systems for animal imaging, and is primarily due to the large dataset employed and the use of inversion methods. Finally, the in vivo imaging capacity is showcased. It is expected that the large dataset collected can enable superior imaging of molecular probes in vivo and improve quantification of fluorescence signatures.
View details for DOI 10.1118/1.1568977
View details for Web of Science ID 000182967800022
View details for PubMedID 12772999
Histopathological validation of a three-dimensional magnetic resonance spectroscopy index as a predictor of tumor presence
JOURNAL OF NEUROSURGERY
2002; 97 (4): 794-802
Data obtained preoperatively from three-dimensional (3D)/proton magnetic resonance (MR) spectroscopy were compared with the results of histopathological assays of tissue biopsies obtained during surgery to verify the sensitivity and specificity of a choline-containing compound-N-acetylaspartate index (CNI) used to distinguish tumor from nontumorous tissue within T2-hyperintense and contrast-enhancing lesions of patients with untreated gliomas. The information gleaned from the biopsy correlation study was used to test the hypothesis that there is metabolically active tumor in nonenhancing regions of the T2-hyperintense lesion that can be detected using MR spectroscopy.Patients suspected of harboring a glioma underwent 3D MR spectroscopy during their preoperative MR imaging examination. Surgical navigation techniques were used to record the location of tissue biopsies collected during open resection of the tumor. A receiver operating curve analysis of the CNI and histological characteristics of specimens at each biopsy location was performed to determine the optimal threshold of the CNI required to separate tumor from nontumorous tissue. Histograms of the CNIs within enhancing and nonenhancing regions of lesions appearing on MR images were generated to determine the spatial distribution of CNIs consistent with tumor.Biopsy samples containing tumor were distinguished from those containing a mixture of normal, edematous, gliotic, and necrotic tissue with 90% sensitivity and 86% specificity by using a CNI threshold of 2.5. The CNIs of nontumorous specimens were significantly different from those of biopsy specimens containing Grade II (p < 0.03), Grade III (p < 0.005), and Grade IV (p < 0.01) tumors. On average, one third to one half of the T2-hyperintense lesion outside the contrast-enhancing lesion contained CNI greater than 2.5.
View details for Web of Science ID 000178626400014
View details for PubMedID 12405365
In vivo molecular imaging for planning radiation therapy of gliomas: an application of 1H MRSI
JOURNAL OF MAGNETIC RESONANCE IMAGING
2002; 16 (4): 464-476
Gliomas are infiltrative lesions that typically have poorly defined margins on conventional magnetic resonance (MR) and computed tomography (CT) images. This presents a considerable challenge for planning radiation and other forms of focal therapy, and introduces the possibility of both under-treating macroscopic tumor, and over-treating regions of normal brain tissue. New therapy systems are able to deliver radiation more precisely and accurately to irregular three-dimensional target volumes, and have placed a premium on definition of the spatial extent of the lesion. Proton MR spectroscopic imaging (H-MRSI) has been proposed as an in vivo molecular imaging technique that assists in targeting and predicts response to radiation therapy for patients with gliomas. The evidence that supports the use of H-MRSI for planning radiation treatment is reviewed, together with the technical requirements for implementing data acquisition and analysis procedures in a clinical setting. Although there is room for improvement in the spatial resolution and chemical specificity obtained at the conventional field strength of 1.5 T, there are clear benefits to integrating H-MRSI into treatment planning and follow-up examinations. Further work is required to integrate the results of the H-MRSI examination into the treatment planning workstation, and to improve the quality of the data using more sensitive phased array coils and higher field strength magnets.
View details for DOI 10.1002/jmri.10183
View details for Web of Science ID 000178445700013
View details for PubMedID 12353260
Metabolic imaging of low-grade gliomas with three-dimensional magnetic resonance spectroscopy
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2002; 53 (5): 1254-1264
The role of radiotherapy (RT) seems established for patients with low-grade gliomas with poor prognostic factors. Three-dimensional (3D) magnetic resonance spectroscopy imaging (MRSI) has been reported to be of value in defining the extent of glioma infiltration. We performed a study examining the impact MRSI would have on the routine addition of 2-3-cm margins around MRI T2-weighted hyperintensity to generate the treatment planning clinical target volume (CTV) for low-grade gliomas.Twenty patients with supratentorial gliomas WHO Grade II (7 astrocytomas, 6 oligoastrocytomas, 7 oligodendrogliomas) underwent MRI and MRSI before surgery. The MRI was contoured manually; the regions of interest included T2 hyperintensity and, if present, regions of contrast enhancement on T1-weighted images. The 3D-MRSI peak parameters for choline and N-acetyl-aspartate, acquired voxel-by-voxel, were categorized using a choline/N-acetyl-aspartate index (CNI), a tool for quantitative assessment of tissue metabolite levels, with CNI 2 being the lowest value corresponding to tumor. CNI data were aligned to MRI and displayed as 3D contours. The relationship between the anatomic and metabolic information on tumor extent was assessed by comparing the CNI contours and other MRSI-derived metabolites to the MRI T2 volume.The limitations in the size of the region "excited" meant that MRSI could be used to evaluate only a median 68% of the T2 volume (range 38-100%), leaving the volume T2c. The CNI 2 volume (median 29 cm(3), range 10-73) was contained totally within the T2c in 55% of patients. In the remaining patients, the volume of CNI 2 extending beyond the T2c was quite small (median 2.3 cm(3), range 1.4-5.2), but was not distributed uniformly about the T2c, extending up to 22 mm beyond it. Two patients demonstrated small regions of contrast enhancement corresponding to the regions of highest CNI. Other metabolites, such as creatine and lactate, seem useful for determining less and more radioresistant areas, respectively.Metabolically active tumor, as detected by MRSI, is restricted mainly to the T2 hyperintensity in low-grade gliomas, but can extend outside it in a limited and nonuniform fashion up to 2 cm. Therefore, a CTV including T2 and areas of CNI extension beyond the T2 hyperintensity would result in a reduction in the size and a change in the shape of the standard clinical target volumes generated by adding uniform margins of 2-3 cm to the T2 hyperintensity.
View details for Web of Science ID 000177217800021
View details for PubMedID 12128127
In Vivo Tomographic Imaging of Near-Infrared Fluorescent Probes
2002; 1 (2): 82-88
Fluorescence imaging is increasingly used to probe protein function and gene expression in live animals. This technology could enhance the study of pathogenesis, drug development, and therapeutic intervention. In this article, we focus on three-dimensional fluorescence observations using fluorescence-mediated molecular tomography (FMT), a novel imaging technique that can resolve molecular function in deep tissues by reconstructing fluorescent probe distributions in vivo. We have compared FMT findings with conventional fluorescence reflectance imaging (FRI) to study protease function in nude mice with subsurface implanted tumors. This validation of FMT with FRI demonstrated the spatial congruence of fluorochrome activation as determined by the two techniques.
View details for Web of Science ID 000209334600003
In-vivo molecular investigations of live tissues using diffracting sources
MEDICAL IMAGE COMPUTING AND COMPUTER-ASSISTED INTERVENTION-MICCAI 2002, PT 1
2002; 2488: 739-745
View details for Web of Science ID 000189412100091
Registration of magnetic resonance spectroscopic imaging to computed tomography for radiotherapy treatment planning
2001; 28 (12): 2489-2496
The incorporation of multiple imaging modalities into radiotherapy treatment planning offers the potential to improve identification of regions of pathology. This work outlines and evaluates a methodology for registration of magnetic resonance images (MRI) and spectroscopic images (MRSI) to computed tomography (CT) images, and visualization of the multimodality data on the treatment planning workstation. Volumetric magnetic resonance images were acquired during an examination prior to the initiation of radiotherapy. Registration between these images and the treatment planning computed tomography images was performed using an automated alignment routine, and was improved manually using an interactive registration tool. The parameters of the alignment were then used to transform the spectroscopic images into the same reference frame. The spectroscopy data were represented in terms of a statistical measure of abnormality, and embedded within the MRI data as overlaid contours. These images were sent via DICOM transfer to the treatment planning workstation. An analysis of the reproducibility of the
View details for DOI 10.1118/1.1420400
View details for Web of Science ID 000172896200013
View details for PubMedID 11797952
MR-spectroscopy guided target delineation for high-grade gliomas
ELSEVIER SCIENCE INC. 2001: 915-928
Functional/metabolic information provided by MR-spectroscopy (MRSI) suggests MRI may not be a reliable indicator of active and microscopic disease in malignant brain tumors. We assessed the impact MRSI might have on the target volumes used for radiation therapy treatment planning for high-grade gliomas.Thirty-four patients (22 Grade III; 12 Grade IV astrocytomas) were evaluated; each had undergone MRI and MRSI studies before surgery. MRI data sets were contoured for T1 region of contrast enhancement (T1), region of necrosis, and T2 region of hyperintensity (T2). The three-dimensional MRSI peak parameters for choline (Cho) and N-acetylaspartate (NAA), acquired by a multivoxel technique, were categorized based on an abnormality index (AI), a quantitative assessment of tissue metabolite levels. The AI data were aligned to the MRI and displayed as three-dimensional contours. AI vs. T conjoint and disjoint volumes were compared.For both grades, although T2 estimated the region at risk of microscopic disease as being as much as 50% greater than by MRSI, metabolically active tumor still extended outside the T2 region in 88% of patients by as many as 28 mm. In addition, T1 suggested a lesser volume and different location of active disease compared to MRSI.The use of MRSI to define target volumes for RT treatment planning would increase, and change the location of, the volume receiving a boost dose as well as reduce the volume receiving a standard dose. Incorporation of MRSI into the treatment-planning process may have the potential to improve control while reducing complications.
View details for Web of Science ID 000169615100010
View details for PubMedID 11429219
Serial proton MR spectroscopic imaging of recurrent malignant gliomas after gamma knife radiosurgery
AMERICAN JOURNAL OF NEURORADIOLOGY
2001; 22 (4): 613-624
The diagnosis of brain tumors after high-dose radiation therapy is frequently limited by the lack of metabolic discrimination available with conventional imaging methods. The purpose of this study was to use proton MR spectroscopy to investigate serial changes in recurrent malignant gliomas after gamma knife radiosurgery to characterize tissue response to high-dose radiation.Eighteen patients with recurrent gliomas were studied with MR imaging and 3D proton MR spectroscopic imaging at the time of radiosurgery and at regular time points thereafter. Choline (Cho) and N-acetyl aspartate levels were calculated on a voxel-by-voxel basis and compared with levels found in normal tissue and with levels observed at previous time points. The results of the spectral analysis were then compared with the radiologic findings. Statistical comparisons were precluded by the small sample sizes involved.Response within the gamma knife target was observed as a reduction of Cho levels and an increase in lactate/lipid levels, typically within 6 months of treatment. Increases in Cho correlated with poor radiologic response and suggested tumor recurrence, confirmed histologically in six cases. The development of a spectral abnormality preceded a coincident increase in contrast enhancement by 1 to 2 months in nine cases.Proton MR spectroscopic imaging provided diagnostic and monitoring information before and after radiosurgery. Evaluation of metabolic changes with proton MR spectroscopy and structural changes with MR imaging improved tissue discrimination and provided correlation with histologic findings.
View details for Web of Science ID 000168156800006
View details for PubMedID 11290467
A preliminary study of the prognostic value of proton magnetic resonance spectroscopic imaging in gamma knife radiosurgery of recurrent malignant gliomas
2000; 46 (2): 319-326
The goal of this study was to investigate the use of proton magnetic resonance spectroscopic imaging as a prognostic indicator in gamma knife radiosurgery of recurrent gliomas.Thirty-six patients with recurrent gliomas were studied with proton magnetic resonance spectroscopic imaging at the time of radiosurgery, and with conventional magnetic resonance imaging examinations at regular time intervals until the initiation of a new treatment strategy. Patients were categorized on the basis of their initial spectroscopic results, and their performance was assessed in terms of change in contrast-enhancing volume, time to further treatment, and survival.The trends in the overall population were toward more extensive increase in the percent contrast-enhancing volume, a decreased time to further treatment, and a reduced survival time for patients with more extensive initial metabolic abnormalities. Statistical analysis of the subpopulation of patients with glioblastoma multiforme found a significant increase in relative contrast-enhancing volume (P < 0.01, Wilcoxon signed-rank test), a decrease in time to further treatment (P < 0.01, log-rank test), and a reduction in survival time (P < 0.01, log-rank test) for patients with regions containing tumor-suggestive spectra outside the gamma knife target, compared with patients exhibiting spectral abnormalities restricted to the gamma knife target. Further studies are needed to establish statistical significance for patients with lower-grade lesions and to confirm the results observed in this study.The pretreatment spectroscopic results provided information that was predictive of outcome for this patient pool, both in local control (change in contrast-enhancing volume) and global outcome (time to further treatment and survival). This modality may have an important role in improving the selection, planning, and treatment process for glioma patients.
View details for Web of Science ID 000085191800028
View details for PubMedID 10690720
- Gamma Knife Radiosurgery for Primary Brain Tumors LINAC and Gamma Knife Radiosurgery (Germano, I.M., ed.) 2000: 189-202
Magnetic resonance spectroscopy guided integrated boost irradiation for high grade gliomas using IMRT
USE OF COMPUTERS IN RADIATION THERAPY
View details for Web of Science ID 000088386600057
- CNN-Based Models for Color Vision and Visual Illusions IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications 1999; 46: 229-238