Clinical Associate Professor, Radiation Oncology - Radiation Physics
Chief of Clinical Physics, Stanford University (2020 - Present)
Chief of Clinical Physics, Loyola University Chicago (2015 - 2020)
Honors & Awards
Jack Fowler Junior Investigator Award, American Association of Physicist in Medicine (AAPM) (7/28/2008)
Young Investigator Symposium Award, AAPM Midwest Chapter (4/17/2010)
Best of Physics Award (co-author), American Society of Therapeutic Radiation Oncology (ASTRO) (10/19/2015)
Boards, Advisory Committees, Professional Organizations
Secretary, AAPM Midwest Chapter (2018 - 2020)
Treasurer, AAPM Midwest Chapter (2016 - 2018)
Board Member At Large, AAPM Midwest Chapter (2014 - 2016)
Member, American Association of Physicists in Medicine (AAPM) (2009 - Present)
Member, American Society of Therapeutic Radiation Oncology (ASTRO) (2011 - Present)
Member, American College of Radiology (ACR) (2016 - Present)
BS, Bogazici University, Turkey, Physics (2000)
MS, Bogazici University, Turkey, Biomedical Engineering (2002)
PhD, University of Southern California, Biomedical Engineering (2007)
Postdoc, Washington University in St. Louis, Medical Physics (2009)
Residency, University of Chicago, Medical Physics (2011)
Image-mode performance characterization of a positron emission tomography subsystem designed for Biology-guided radiotherapy (BgRT).
The British journal of radiology
OBJECTIVES: In this study, we characterize the imaging-mode performance of the positron emission tomography (PET) subsystem of the RefleXion X1 machine using the NEMA NU-2 2018 standard.METHODS: The X1 machine consists of two symmetrically opposing 900 arcs of PET detectors incorporated into the architecture of a ring-gantry linear accelerator rotating up to 60RPM. PET emissions from a tumor are detected by the PET detectors and used to guide the delivery of radiation beam. Imaging performance of the PET subsystem on X1 machine was evaluated based on1 sensitivity of the PET detectors,2 spatial resolution,3 count-loss performance,4 Image quality, and daily system performance check.RESULTS: PET subsystem sensitivity was measured as 0.183 and 0.161 cps/kBq at the center and off-center positions, respectively. Spatial resolution: average FWHM values of 4.3, 5.1, and 6.7mm for the point sources at 1, 10, and 20cm off center, respectively were recorded. For count loss, max NECR: 2.63 kcps, max true coincidence rate: 5.56 kcps, and scatter fraction: 39.8%. The 10mm sphere was not visible. Image-quality contrast values were: 29.6%, 64.9%, 66.5%, 81.8%, 81.2%, and background variability: 14.8%, 12.4%, 10.3%, 8.8%, 8.3%, for the 13, 17, 22, 28, 37mm sphere sizes, respectively.CONCLUSIONS: When operating in an imaging mode, the spatial resolution and image contrast of the X1 PET subsystem were comparable to those of typical diagnostic imaging systems for large spheres, while the sensitivity and count rate were lower due to the significantly smaller PET detector area in the X1 system. Clinical efficacy when used in BgRT remains to be validated.ADVANCES IN KNOWLEDGE: This is the first performance evaluation of the PET subsystem on the novel BgRT machine. The dual arcs rotating PET subsystem on RefleXion X1 machine performance is comparable to those of the typical diagnostic PET system based on the spatial resolution and image contrast for larger spheres.
View details for DOI 10.1259/bjr.20220387
View details for PubMedID 36317922
Impact of respiratory motion on lung dose during total marrow irradiation.
Frontiers in oncology
2022; 12: 924961
We evaluated the impact of respiratory motion on the lung dose during linac-based intensity-modulated total marrow irradiation (IMTMI) using two different approaches: (1) measurement of doses within the lungs of an anthropomorphic phantom using thermoluminescent detectors (TLDs) and (2) treatment delivery measurements using ArcCHECK where gamma passing rates (GPRs) and the mean lung doses were calculated and compared with and without motion. In the first approach, respiratory motions were simulated using a programmable motion platform by using typical published peak-to-peak motion amplitudes of 5, 8, and 12 mm in the craniocaudal (CC) direction, denoted here as M1, M2, and M3, respectively, with 2 mm in both anteroposterior (AP) and lateral (LAT) directions. TLDs were placed in five selected locations in the lungs of a RANDO phantom. Average TLD measurements obtained with motion were normalized to those obtained with static phantom delivery. The mean dose ratios were 1.01 (0.98-1.03), 1.04 (1.01-1.09), and 1.08 (1.04-1.12) for respiratory motions M1, M2, and M3, respectively. To determine the impact of directional respiratory motion, we repeated the experiment with 5-, 8-, and 12-mm motion in the CC direction only. The differences in average TLD doses were less than 1% when compared with the M1, M2, and M3 motions indicating a minimal impact from CC motion on lung dose during IMTMI. In the second experimental approach, we evaluated extreme respiratory motion 15 mm excursion in only the CC direction. We placed an ArcCHECK device on a commercial motion platform and delivered the clinical IMTMI plans of five patients. We compared, with and without motion, the dose volume histograms (DVHs) and mean lung dose calculated with the ArcCHECK-3DVH tool as well as GPR with 3%, 5%, and 10% dose agreements and a 3-mm constant distance to agreement (DTA). GPR differed by 11.1 ± 2.1%, 3.8 ± 1.5%, and 0.1 ± 0.2% with dose agreement criteria of 3%, 5%, and 10%, respectively. This indicates that respiratory motion impacts dose distribution in small and isolated parts of the lungs. More importantly, the impact of respiratory motion on the mean lung dose, a critical indicator for toxicity in IMTMI, was not statistically significant (p > 0.05) based on the Student's t-test. We conclude that most patients treated with IMTMI will have negligible dose uncertainty due to respiratory motion. This is particularly reassuring as lung toxicity is the main concern for future IMTMI dose escalation studies.
View details for DOI 10.3389/fonc.2022.924961
View details for PubMedID 36330489
View details for PubMedCentralID PMC9622752
Feasibility of Single Fraction Brain Metastases Radiotherapy in a Novel Ring Gantry Treatment System
LIPPINCOTT WILLIAMS & WILKINS. 2022: S56
View details for Web of Science ID 000847787800112
Design and validation of a dosimetric comparison scheme tailored for ultra-high dose-rate electron beams to support multicenter FLASH preclinical studies.
Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology
We describe a multicenter cross validation of ultra-high dose rate (UHDR) (>= 40 Gy/s) irradiation in order to bring a dosimetric consensus in absorbed dose to water. UHDR refers to dose rates over 100-1000 times those of conventional clinical beams. UHDR irradiations have been a topic of intense investigation as they have been reported to induce the FLASH effect in which normal tissues exhibit reduced toxicity relative to conventional dose rates. The need to establish optimal beam parameters capable of achieving the in vivo FLASH effect has become paramount. It is therefore necessary to validate and replicate dosimetry across multiple sites conducting UHDR studies with distinct beam configurations and experimental set-ups.Using a custom cuboid phantom with a cylindrical cavity (5 mm diameter by 10.4 mm length) designed to contain three type of dosimeters (thermoluminescent dosimeters (TLDs), alanine pellets, and Gafchromic films), irradiations were conducted at expected doses of 7.5 to 16 Gy delivered at UHDR or conventional dose rates using various electron beams at the Radiation Oncology Departments of the CHUV in Lausanne, Switzerland and Stanford University, CA.Data obtained between replicate experiments for all dosimeters were in excellent agreement (+/- 3 %). In general, films and TLDs were in closer agreement with each other, while alanine provided the closest match between the expected and measured dose, with certain caveats related to absolute reference dose.In conclusion, successful cross-validation of different electron beams operating under different energies and configurations lays the foundation for establishing dosimetric consensus for UHDR irradiation studies, and, if widely implemented, decrease uncertainty between different sites investigating the mechanistic basis of the FLASH effect.
View details for DOI 10.1016/j.radonc.2022.08.023
View details for PubMedID 36030934
Treatment planning system commissioning of the first clinical biology-guided radiotherapy machine.
Journal of applied clinical medical physics
PURPOSE: The RefleXion X1 is a novel radiotherapy machine designed for image-guided radiotherapy (IGRT) and biology-guided radiotherapy (BgRT). Its treatment planning system (TPS) generates IMRT and SBRT plans for a 6MV-FFF beam delivered axially via 50 firing positions with the couch advancing every 2.1mm. The purpose of this work is to report the TPS commissioning results for the first clinical installation of RefleXion X1.METHODS: CT images of multiple phantoms were imported into the RefleXion TPS to evaluate the accuracy of data transfer, anatomical modeling, plan evaluation, and dose calculation. Comparisons were made between the X1, Eclipse, and MIM. Dosimetric parameters for open static fields were evaluated in water and heterogeneous slab phantoms. Representative clinical IMRT and SBRT cases were planned and verified with ion chamber, film, and ArcCHECK@ measurements. The agreement between TPS and measurements for various clinical plans was evaluated using Gamma analysis with a criterion of 3%/2mm for ArcCHECK@ and film. End-to-end (E2E) testing was performed using anthropomorphic head and lung phantoms.RESULTS: The average difference between the TPS-reported and known HU values was -1.4 ± 6.0 HU. For static fields, the agreements between the TPS-calculated and measured PDD10 , crossline profiles, and inline profiles (FWHM) were within 1.5%, 1.3%, and 0.5mm, respectively. Measured output factors agreed with the TPS within 1.3%. Measured and calculated dose for static fields in heterogeneous phantoms agreed within 2.5%. The ArcCHECK@ mean absolute Gamma passing rate was 96.4% ± 3.4% for TG 119 and TG 244 plans and 97.8% ± 3.6% for the 21 clinical plans. E2E film analysis showed 0.8mm total targeting error for isocentric and 1.1mm for off-axis treatments.CONCLUSIONS: The TPS commissioning results of the RefleXion X1 TPS were within the tolerances specified by AAPM TG 53, MPPG 5.a, TG 119, and TG 148. A subset of the commissioning tests has been identified as baseline data for an ongoing QA program.
View details for DOI 10.1002/acm2.13638
View details for PubMedID 35644039
Beam commissioning of the first clinical biology-guided radiotherapy system.
Journal of applied clinical medical physics
This study reports the beam commissioning results for the first clinical RefleXion Linac.METHODS: The X1 produces a 6MV photon beam and the maximum clinical field size is 40*2cm2 at source-to-axis distance of 85cm. Treatment fields are collimated by a binary multileaf collimator (MLC) system with 64 leaves with width of 0.625cm and y-jaw pairs to provide either a 1 or 2cm opening. The mechanical alignment of the radiation source, the y-jaw, and MLC were checked with film and ion chambers. The beam parameters were characterized using a diode detector in a compact water tank. In-air lateral profiles and in-water percentage depth dose (PDD) were measured for beam modeling of the treatment planning system (TPS). The lateral profiles, PDDs, and output factors were acquired for field sizes from 1.25*1 to 40*2cm2 field to verify the beam modeling. The rotational output variation and synchronicity were tested to check the gantry angle, couch motion, and gantry rotation.RESULTS: The source misalignments were 0.049mm in y-direction, 0.66% out-of-focus in x-direction. The divergence of the beam axis was 0.36mm with a y-jaw twist of 0.03°. Clinical off-axis treatment fields shared a common center in y-direction were within 0.03mm. The MLC misalignment and twist were 0.57mm and 0.15°. For all measured fields ranging from the size from 1.25*1 to 40*2cm2 , the mean difference between measured and TPS modeled PDD at 10cm depth was -0.3%. The mean transverse profile difference in the field core was -0.3%±1.1%. The full-width half maximum (FWHM) modeling was within 0.5mm. The measured output factors agreed with TPS within 0.8%.CONCLUSIONS: This study summarizes our specific experience commissioning the first novel RefleXion linac, which may assist future users of this technology when implementing it into their own clinics.
View details for DOI 10.1002/acm2.13607
View details for PubMedID 35482018
IMRT and SBRT Treatment Planning Study for the First Clinical Biology-Guided Radiotherapy System.
Technology in cancer research & treatment
2022; 21: 15330338221100231
Purpose: The first clinical biology-guided radiation therapy (BgRT) system-RefleXionTM X1-was installed and commissioned for clinical use at our institution. This study aimed at evaluating the treatment plan quality and delivery efficiency for IMRT/SBRT cases without PET guidance. Methods: A total of 42 patient plans across 6 cancer sites (conventionally fractionated lung, head, and neck, anus, prostate, brain, and lung SBRT) planned with the EclipseTM treatment planning system (TPS) and treated with either a TrueBeam or Trilogy were selected for this retrospective study. For each Eclipse VMAT plan, 2 corresponding plans were generated on the X1 TPS with 10mm jaws (X1-10mm) and 20mm jaws (X1-20mm) using our institutional planning constraints. All clinically relevant metrics in this study, including PTV D95%, PTV D2%, Conformity Index (CI), R50, organs-at-risk (OAR) constraints, and beam-on time were analyzed and compared between 126 VMAT and RefleXion plans using paired t-tests. Results: All but 3 planning metrics were either equivalent or superior for the X1-10mm plans as compared to the Eclipse VMAT plans across all planning sites investigated. The Eclipse VMAT and X1-10mm plans generally achieved superior plan quality and sharper dose fall-off superior/inferior to targets as compared to the X1-20mm plans, however, the X1-20mm plans were still considered acceptable for treatment. On average, the required beam-on time increased by a factor of 1.6 across all sites for X1-10mm compared to X1-20mm plans. Conclusions: Clinically acceptable IMRT/SBRT treatment plans were generated with the X1 TPS for both the 10mm and 20mm jaw settings.
View details for DOI 10.1177/15330338221100231
View details for PubMedID 35579876
Small field measurement and monte carlo model validation of a novel image-guided radiotherapy system.
PURPOSE: The RefleXionTM X1 is a novel radiotherapy system that is designed for image-guided radiotherapy and, eventually, biology-guided radiotherapy (BgRT). BgRT is a treatment paradigm that tracks tumor motion using real-time positron emission signals. This study reports the small field measurement results and the validation of a Monte Carlo (MC) model of the first clinical RefleXion unit.METHODS: The RefleXion linear accelerator (linac) produces a 6 MV flattening filter free (FFF) photon beam and consists of a binary multi-leaf collimator (MLC) system with 64 leaves and two pairs of y-jaws. The maximum clinical field size achievable is 400 * 20 mm2 . The y-jaws provide either a 10 mm or 20 mm opening at source-to-axis distance (SAD) of 850 mm. The width of each MLC leaf at SAD is 6.25 mm. Percentage depth doses (PDDs) and relative beam profiles were acquired using an Edge diode detector in a water tank for field sizes from 12.5 * 10 mm2 to 100 * 20 mm2 . Beam profiles were also measured using films. Output factors of fields ranging from 6.25 * 10 mm2 to 100 * 20 mm2 were measured using W2 scintillator detector, Edge detector, and films. Output correction factors k of the Edge detector for RefleXion were calculated. A MC model of the linac including pre-MLC beam sources and detailed structures of MLC and lower y-jaws was validated against the measurements. Simulation codes BEAMnrc and GATE were utilized.RESULTS: The diode measured PDD at 10 cm depth (PDD10) increases from 53.6% to 56.9% as the field opens from 12.5 * 10 mm2 to 100 * 20 mm2 . The W2-measured output factor increases from 0.706 to 1 as the field opens from 6.25 * 10 mm2 to 100 * 20 mm2 (reference field size). The output factors acquired by diode and film differ from the W2 results by 1.65% (std = 1.49%) and 2.09% (std = 1.41%) on average, respectively. The profile penumbra and full width half maximum (FWHM) measured by diode agree well with the film results with a deviation of 0.60 mm and 0.73% on average, respectively. The averaged beam profile consistency calculated between the diode and film measured profiles among different depths is within 1.72%. By taking the W2 measurements as the ground truth, the output correction factors k for Edge detector ranging from 0.958 to 1 were reported. For the MC model validation, the simulated PDD10 agreed within 0.6% to the diode measurement. The MC simulated output factor differed from the W2 results by 2.3% on average (std = 3.7%) while the MC simulated beam penumbra differed from the diode results by 0.67 mm on average (std = 0.42 mm). The MC FWHM agreed with the diode results to within 1.40% on average. The averaged beam profile consistency calculated between the diode and MC profiles among different depths is less than 1.29%.CONCLUSIONS: This study represents the first small field dosimetry of a clinical RefleXion system. A complete and accurate MC model of the RefleXion linac has been validated. This article is protected by copyright. All rights reserved.
View details for DOI 10.1002/mp.15273
View details for PubMedID 34628666
Uterine perforation during brachytherapy for cervical cancer: Complications, outcomes, and best practices for forward treatment planning and management.
PURPOSE: The purpose of the study was to determine the incidence of uterine perforations, review the associated complications, and propose guidelines for management of perforations after brachytherapy.METHODS AND MATERIALS: A retrospective chart review was conducted for all patients with cervical cancer who received single or multiple high-dose-rate brachytherapy implants between April 2006 and May 2017at a single academic institution. CT and MRI images were retrospectively evaluated to record incidences of uterine perforation of tandem during brachytherapy. Acute and long-term complications during and after treatment were scored using the Common Terminology Criteria for Adverse Events, Version 4.0, of the National Cancer Institute.RESULTS: A total of 123 patients were included in the study. Perforations were observed in 22 patients (17.9%) with 31 (6.4%) of the 482 total implants. Of the different categories of adverse events, only the rate of acute infectious complications among those with perforations (n= 3, 13.6%) versus those without perforations (n= 3, 3.0%) was significant (p= 0.040). Two of the three perforated patients with acute infections had mild urinary tract infections, and all resolved without complications or treatment delays. The remaining one patient had a frank perforation of the anterior uterine wall with a subsequent Grade 3 pyometra infection despite administration of prophylactic antibiotics and 1-week treatment delay. This case was eventually resolved with cervical dilation and evacuation of fluid. Long-term complications were not different between the two arms.CONCLUSIONS: Patients with cervical cancer with uterine perforations may be able to safely proceed with brachytherapy treatment without delay or need for prophylactic antibiotics in the acute setting. Further validating data would be able to assist in establishing a new standard of care and help prevent unnecessary and harmful breaks during treatment.
View details for DOI 10.1016/j.brachy.2021.02.001
View details for PubMedID 33741275
Characterization of Markerless Tumor Tracking Using the On-Board Imager of a Commercial Linear Accelerator Equipped With Fast-kV Switching Dual-Energy Imaging.
Advances in radiation oncology
2020; 5 (5): 1006–13
Purpose: To describe and characterize fast-kV switching, dual-energy (DE) imaging implemented within the on-board imager of a commercial linear accelerator for markerless tumor tracking (MTT).Methods and Materials: Fast-kV switching, DE imaging provides for rapid switching between programmed tube voltages (ie, 60 and 120 kVp) from one image frame to the next. To characterize this system, the weighting factor used for logarithmic subtraction and signal difference-to-noise ratio were analyzed as a function of time and frame rate. MTT was evaluated using a thorax motion phantom and fast kV, DE imaging was compared versus single energy (SE) imaging over 360 degrees of rotation. A template-based matching algorithm was used to track target motion on both DE and SE sequences. Receiver operating characteristics were used to compare tracking results for both modalities.Results: The weighting factor was inversely related to frame rate and stable over time. After applying the frame rate-dependent weighting factor, the signal difference-to-noise ratio was consistent across all frame rates considered for simulated tumors ranging from 5 to 25 mm in diameter. An analysis of receiver operating characteristics curves showed improved tracking with DE versus SE imaging. The area under the curve for the 10-mm target ranged from 0.821 to 0.858 for SE imaging versus 0.968 to 0.974 for DE imaging. Moreover, the residual tracking errors for the same target size ranged from 2.02 to 2.18 mm versus 0.79 to 1.07 mm for SE and DE imaging, respectively.Conclusions: Fast-kV switching, DE imaging was implemented on the on-board imager of a commercial linear accelerator. DE imaging resulted in improved MTT accuracy over SE imaging. Such an approach may have application for MTT of patients with lung cancer receiving stereotactic body radiation therapy, particularly for small tumors where MTT with SE imaging may fail.
View details for DOI 10.1016/j.adro.2020.01.008
View details for PubMedID 33089019
A practical method for quantifying dose in bone and lung using TLDs when using 6 and 15 MV photon beams.
Physics in medicine and biology
This paper presents a practical method for converting dose measured with thermoluminescent dosimeters (TLD) to dose in lung and bone for 6 MV and 15 MV photon beams. Monte Carlo (MC) simulations and Burlin cavity theory calculations were performed to calculate fmediumTLD, the dose-to-TLD to dose-to-medium conversion factor. A practical method was proposed for converting TLD-measured-dose to dose-in-medium using the TLD dose calibration in water and fwatermedium, dose-to-medium to dose-to-water conversion factor. Theoretical calculations for fwatermediumwere performed using photon spectrum weighted parameters and were compared with MC simulations. Verification of the proposed method was done using phantoms having either bone or lung equivalent slabs stacked in between solid water slabs. Percent depth dose (PDD) curves were measured using 0.089 cm thick LiF:Mg,Ti (TLD-100) dosemeters placed at various depths within these phantoms. They were then corrected with fwatermediumfactors using the proposed dose conversion method, and were compared with the MC simulations. For 6 MV beam, the MC calculated fwatermediumfactors were 0.942 and 1.002 for bone and lung, and for 15 MV it was 0.927 and 1.005 for bone and lung, respectively. The difference between the MC simulated and spectrum weighted theoretical fwatermediumfactors were within 3 % for both lung and bone. The PDD curves measured with TLD-100 chips that were corrected using the proposed method agreed well within 1.5% of the MC simulated PDD curves for both the water/lung/water and water/bone/water phantoms. The dose-to-medium correction using MC simulated fwatermediumis convenient, easy, and accurate. Therefore, it can be used instead of Burlin cavity theory, especially in media with high atomic numbers such as bone for accurate dose quantification.
View details for DOI 10.1088/1361-6560/ab735d
View details for PubMedID 32028274
Adaptive weighted log subtraction based on neural networks for markerless tumor tracking using dual-energy fluoroscopy
To present a novel method, based on convolutional neural networks (CNN), to automate weighted log subtraction (WLS) for dual-energy (DE) fluoroscopy to be used in conjunction with markerless tumor tracking (MTT).A CNN was developed to automate WLS (aWLS) of DE fluoroscopy to enhance soft tissue visibility. Briefly, this algorithm consists of two phases: training a CNN architecture to predict pixel-wise weighting factors followed by application of WLS subtraction to reduce anatomical noise. To train the CNN, a custom phantom was built consisting of aluminum (Al) and acrylic (PMMA) step wedges. Per-pixel ground truth (GT) weighting factors were calculated by minimizing the contrast of Al in the step wedge phantom to train the CNN. The pretrained model was then utilized to predict pixel-wise weighting factors for use in WLS. For comparison, the weighting factor was manually determined in each projection (mWLS). A thorax phantom with five simulated spherical targets (5-25 mm) embedded in a lung cavity, was utilized to assess aWLS performance. The phantom was imaged with fast-kV dual-energy (120 and 60 kVp) fluoroscopy using the on-board imager of a commercial linear accelerator. DE images were processed offline to produce soft tissue images using both WLS methods. MTT was compared using soft tissue images produced with both mWLS and aWLS techniques.Qualitative evaluation demonstrated that both methods achieved soft tissue images with similar quality. The use of aWLS increased the number of tracked frames by 1-5% compared to mWLS, with the largest increase observed for the smallest simulated tumors. The tracking errors for both methods produced agreement to within 0.1 mm.A novel method to perform automated WLS for DE fluoroscopy was developed. Having similar soft tissue quality as well as bone suppression capability as mWLS, this method allows for real-time processing of DE images for MTT.
View details for DOI 10.1002/mp.13941
View details for Web of Science ID 000506456400001
View details for PubMedID 31797397
Failure mode and effects analysis of linac-based liver stereotactic body radiotherapy.
PURPOSE: Although stereotactic body radiation therapy (SBRT) is an attractive noninvasive approach for liver irradiation, it presents specific challenges associated with respiration-induced liver motion, daily tumor localization due to liver deformation, and poor visualization of target with respect to adjacent normal liver in computed tomography (CT). We aim to identify potential hazards and develop a set of mitigation strategies to improve the safety of our liver SBRT program, using failure mode and effect analysis (FMEA).MATERIALS AND METHODS: A multidisciplinary group consisting of two physicians, three physicists, two dosimetrists, and two therapists was formed. A process map covering ten major stages of the liver SBRT program from the initial diagnosis to posttreatment follow-up was generated. A total of 102 failure modes (FM), together with their causes and effects, were identified. The occurrence (O), severity (S), and lack of detectability (D) were independently scored using a scale from 1 (lowest risk) to 10 (largest risk). The ranking was done using the risk probability number (RPN) defined as the product of average O, S, and D numbers for each mode. Two fault tree analyses were performed. The failure modes with the highest RPN values as well as highest severity score were considered for investigation and a set of mitigation strategies was developed to address these.RESULTS: The median RPN (RPNmed ) values for all modes ranged from of 9 to 105 and the highest median S score (Smed ) was 8. Fourteen FMs were identified to be significant by both RPNmed and Smed (top ten RPNmed ranked and highest Smed FMs) and 12 of them were considered for risk mitigation efforts. The remaining two were omitted due to either sufficient checks already in place, or lack of practical mitigation strategies. Implemented measures consisted of five physics tasks, two physician tasks, and three workflow changes.CONCLUSIONS: The application of FMEA to our liver SBRT program led to the identification of potential FMs and allowed improvement measures to enhance the safety of our clinical practice.
View details for DOI 10.1002/mp.13965
View details for PubMedID 31837024
ENERGY RESPONSE FACTOR OF BEO DOSEMETER CHIPS: A MONTE CARLO SIMULATION AND GENERAL CAVITY THEORY STUDY
RADIATION PROTECTION DOSIMETRY
2019; 185 (3): 303–9
The objective of this study is to determine the energy response factors for BeO optically simulated dosemeter (OSLD) using general cavity theory and Monte Carlo (MC) simulations. A virtual phantom is constructed in EGSnrc MC program and energy response of BeO OSLDs were simulated at 5 cm depth for x-ray beams ranging from 1.25 to 25 MV and at 2 cm for beams with <250 kV including ISO 4037 narrow beam energies in a virtual water phantom. The energy response factor for a given radiation quality relative to 60Co was determined for BeO and compared to the Al2O3:C and LiF:Mg,Ti dosemeters. Burlin cavity theory calculations were done using mean photon energy (MPE) of the beam spectra, while EGSnrc software package was used to carry out MC simulation of full spectra. The cavity theory and MC methods agreed well within the 0.7%. Energy response of x-ray beams at MV range showed a maximum of 1.5% under-response. At energies higher than 150 kV (105 keV MPE) showed no significant difference while a significant under-response were observed at 100 kV (53 keV MPE) and 50 kV (29 keV MPE), ~8 and ~12%, respectively. BeO, Al2O3:C and LiF:Mg,Ti dosemeters exhibited very similar energy response at higher energies mainly in the MeV range. At 50 kV (29 keV MPE), however, BeO dosemeter under responded by a factor of 0.878, while Al2O3:C and LiF:Mg,Ti dosemeters over responded by a factor of 3.2 and 1.44, respectively. Furthermore, at low energies, BeO energy response showed dependence on photon spectra. For instance, at 100 kV, the difference was ~8, ~6 and 2% for 53, 60 and 83 keV MPE (ISO 4037N-100), respectively. Furthermore, calibration with 137Cs instead of 60Co resulted up to 1.8% differences in energy response. Both energy spectrum and calibration methods make considerable differences in energy response of OSLDs. This study concludes that BeO chips are nearly energy independent at energies higher than 100 keV MPE, while Al2O3:C dosemeters show an extremely enhanced energy-response ranging between 1.44 and 3.2 at energies between 170 and 29 keV MPE mainly due to dominance of photoelectric effect.
View details for DOI 10.1093/rpd/ncz010
View details for Web of Science ID 000509466900004
View details for PubMedID 30806472
Markerless tumor tracking using fast-kV switching dual-energy fluoroscopy on a benchtop system
2019; 46 (7): 3235–44
View details for DOI 10.1002/mp.13573
View details for Web of Science ID 000475671900028
The Impact of Transitioning to Prospective Contouring and Planning Rounds as Peer Review.
Advances in radiation oncology
2019; 4 (3): 532–40
Purpose: Our peer-review program previously consisted of weekly chart rounds performed before the end of the first week of treatment. In order to perform peer review before the start of treatment when possible, we implemented daily prospective contouring and planning rounds (CPR).Methods and materials: At the time of computed tomography simulation, patients were categorized by the treating physician into 5 treatment groups based on urgency and complexity (ie, standard, urgent, palliative nonemergent, emergent, and special procedures). A scoring system was developed to record the outcome of case presentations, and the results of the CPR case presentations were compared with the time period 2.5years before CPR implementation, for which peer review was performed retrospectively.Results: CPR was implemented on October 1, 2015, and a total of 4759 patients presented for care through May 31, 2018. The majority were in the standard care path (n=3154; 66.3%). Among the remainder of the charts, 358 (7.5%), 430 (9.0%), and 179 (3.8%) cases were in the urgent, nonemergent palliative, and emergent care paths, respectively. The remaining patients were in the special procedures group, representing brachytherapy and stereotactic radiosurgery. A total of 125 patients (2.6%) required major changes and were re-presented after the suggested modifications, 102 patients (2.1%) had minor recommendations that did not require a repeat presentation, and 247 cases (5.2%) had minor documentation-related recommendations that did not require editing of the contours. In the 2.5years before the implementation, records of a total of 1623 patients were reviewed, and only 9 patients (0.6%) had minor recommendation for change. The remainder was noted as complete agreement.Conclusions: Contouring and planning rounds were successfully implemented at our clinic. Pretreatment and, most often, preplanning review of contours and directives allows for a more detailed review and changes to be made early on in the treatment planning process. When compared with historical case presentations, the CPR method made our peer review more thorough and improved standardization.
View details for DOI 10.1016/j.adro.2019.03.004
View details for PubMedID 31360810
Markerless Tumor Tracking using Fast-kV Switching Dual Energy Fluoroscopy on a Benchtop System.
PURPOSE: To evaluate markerless tumor tracking (MTT) using fast-kV switching dual energy (DE) fluoroscopy on a bench top system.METHODS: Fast-kV-switching DE fluoroscopy was implemented on a bench top which includes a turntable stand, flat panel detector, and x-ray tube. The customized generator firmware enables consecutive x-ray pulses that alternate between programmed high and low energies (e.g. 60 and 120 kVp) with a maximum frame rate of 15 Hz. In-house software was implemented to perform weighted DE subtraction of consecutive images to create an image sequence that removes bone and enhances soft tissues. The weighting factor was optimized based on gantry angle. To characterize this system, a phantom was used that simulates the chest anatomy and tumor motion in the lung. Five clinically relevant tumor sizes (5-25 mm diameter) were considered. The targets were programmed to move in the inferior-superior direction of the phantom, perpendicular to the x-ray beam, using a cos4 waveform to mimic respiratory motion. Target inserts were then tracked with MTT software using a template matching method. The optimal computed tomography (CT) slice thickness for template generation was also evaluated. Tracking success rate and accuracy were calculated in regions of the phantom where the target overlapped ribs vs. spine, to compare the performance of single energy (SE) and DE imaging methods.RESULTS: For the 5 mm target, a CT slice thickness of 0.75 mm resulted in the lowest tracking error. For the larger targets (≥ 10 mm) a CT slice thickness ≤ 2 mm resulted in comparable tracking errors for SE and DE images. Overall DE imaging improved MTT accuracy, relative to SE imaging, for all tumor targets in a rotational acquisition. Compared to SE, DE imaging increased tracking success rate of small target inserts (5 and 10 mm). For fast motion tracking, success rates improved from 23% to 64% and 74% to 90% for 5 and 10 mm targets inserts overlapping ribs, respectively. For slow moving targets success rates improved from 19% to 59% and 59% to 91% in 5 and 10 mm targets overlapping the ribs, respectively. Similar results were observed when the targets overlapped the spine. For larger targets (≥ 15 mm) tracking success rates were comparable using SE and DE imaging.CONCLUSION: This work presents the first results of MTT using fast-kV switching DE fluoroscopy. Using DE imaging has improved the tracking accuracy of MTT, especially for small targets. The results of this study will guide the future implementation of fast-kV switching DE imaging using the on-board imager of a linear accelerator. This article is protected by copyright. All rights reserved.
View details for PubMedID 31059124
Fast-switching dual energy cone beam computed tomography using the on-board imager of a commercial linear accelerator.
Physics in medicine and biology
To evaluate fast-kV switching (FS) dual energy (DE) cone beam computed tomography (CBCT) using the on-board imager (OBI) of a commercial linear accelerator to produce virtual monoenergetic (VM) and relative electron density (RED) images.Using an analytical model, CBCT phantom projections obtained at 80 and 140 kVp with FS imaging, were decomposed into equivalent thicknesses of Al and PMMA. All projections were obtained with the titanium foil and bowtie filter in place. Basis material projections were then recombined to create VM images by using the linear attenuation coefficients at the specified energy for each material. Similarly, RED images were produced by replacing the linear attenuation values of Al and PMMA by their respective RED values in the projection space. VM and RED images were reconstructed using Feldkamp-Davis-Kress (FDK) and iterative algorithms. Hounsfield units, contrast-to-noise ratio (CNR) and RED values were compared against known values.The results after VM-CBCT production showed good material decomposition and consistent HUVM values, with measured root mean square errors (RMSE) from theoretical values, after FDK reconstruction, of 20.5, 5.7, 12.8 and 21.7 HU for 50, 80, 100 and 150 keV, respectively. The largest CNR improvements were observed for the 50 keV VM images. Image noise was reduced up to 28% in the VM-CBCT images after iterative image reconstruction. Relative electron density values measured for our method resulted in a mean percentage error of 0.0 ± 1.8%.This study describes a method to generate VM-CBCT and RED images using FS-DE scans obtained using the OBI of a linac, including the effects of the bowtie filter. The creation of VM and RED images increases the dynamic range of CBCT images, and provides additional data that may be used for adaptive radiotherapy, and on table verification for radiotherapy treatments.
View details for DOI 10.1088/1361-6560/ab5c35
View details for PubMedID 31775131
Transitioning From a Low-Dose-Rate to a High-Dose-Rate Prostate Brachytherapy Program: Comparing Initial Dosimetry and Improving Workflow Efficiency Through Targeted Interventions.
Advances in radiation oncology
2019; 4 (1): 103–11
Purpose: We transitioned from a low-dose-rate (LDR) to a high-dose-rate (HDR) prostate brachytherapy program. The objective of this study was to describe our experience developing a prostate HDR program, compare the LDR and HDR dosimetry, and identify the impact of several targeted interventions in the HDR workflow to improve efficiency.Methods and Materials: We performed a retrospective cohort study of patients treated with LDR or HDR prostate brachytherapy. We used iodine-125 seeds (145 Gy as monotherapy, and 110 Gy as a boost) and preoperative planning for LDR. For HDR, we used iridium-192 (13.5 Gy * 2 as monotherapy and 15 Gy * 1 as a boost) and computed tomography-based planning. Over the first 18 months, we implemented several targeted interventions into our HDR workflow to improve efficiency. To evaluate the progress of the HDR program, we used linear mixed-effects models to compare LDR and HDR dosimetry and identify changes in the implant procedure and treatment planning durations over time.Results: The study cohort consisted of 122 patients (51 who received LDR and 71 HDR). The mean D90 was similar between patients who received LDR and HDR (P = .28). HDR mean V100 and V95 were higher (P < .0001), but mean V200 and V150 were lower (P < .0001). HDR rectum V100 and D1cc were lower (P < .0001). The HDR mean for the implant procedure duration was shorter (54 vs 60 minutes; P = .02). The HDR mean for the treatment planning duration dramatically improved with the implementation of targeted workflow interventions (3.7 hours for the first quartile to 2.0 hours for the final quartile; P < .0001).Conclusions: We successfully developed a prostate HDR brachytherapy program at our institution with comparable dosimetry to our historic LDR patients. We identified several targeted interventions that improved the efficiency of treatment planning. Our experience and workflow interventions may help other institutions develop similar HDR programs.
View details for DOI 10.1016/j.adro.2018.10.004
View details for PubMedID 30706017
A novel phantom for characterization of dual energy imaging using an on-board imaging system.
Physics in medicine and biology
Dual-energy (DE) imaging using an on-board imager (OBI) is being considered for real-time tumor tracking purposes. We describe here a custom phantom designed to optimize DE imaging parameters using the OBI of a commercial linear accelerator. The phantom was constructed of lung-, tissue- and bone-equivalent material slabs. Five simulated tumors located at two different depths were encased in the lung-equivalent materials. Two slabs with bone-equivalent material inserts were constructed to simulate ribs, which overlap the simulated tumors. DE bone suppression was performed using a weighted logarithmic subtraction based on an iterative method that minimized the contrast between simulated bone- and lung-equivalent materials. The phantom was subsequently used to evaluate different combinations of high-low energy pairs based on the signal-difference-to-noise ratio (SDNR) metric. The results show a strong correlation between tumor visibility and selected energy pairs, where higher energy separation leads to larger SDNR values. To evaluate the effect of image post-processing methods on tumor visibility, an anti-correlated noise reduction (ACNR) and adaptive kernel scatter correction methods were applied to subsequent DE images. Application of the ACNR technique approximately doubled the SDNR values, hence increasing tumor visibility, while scatter correction had little effect on SDNR values. This phantom allows for quick image acquisition and optimization of imaging parameters and weighting factors. Optimized DE imaging increases soft tissue visibility and may enhance automated lung tumor tracking allowing for real-time adaptive radiotherapy.
View details for DOI 10.1088/1361-6560/aaf9dd
View details for PubMedID 30566913
Can MRI-only replace MRI-CT planning with a titanium tandem and ovoid applicator?
2018; 17 (5): 747–52
To evaluate dosimetric differences between MRI-only and MRI-CT planning with a titanium tandem and ovoid applicator to determine if all imaging and planning goals can be achieved with MRI only.We evaluated 10 patients who underwent MRI-CT-based cervical brachytherapy with a titanium tandem and ovoid applicator. High-risk clinical target volume and organs at risk were contoured on the 3D T2 MRI, which were transferred to the co-registered CT, where the applicator was identified. Retrospectively, three planners independently delineated the applicator on the axial 3D T2 MRI while blinded to the CT. Identical dwell position times in the delivered plan were loaded. Dose-volume histogram parameters were compared to the previously delivered MRI-CT plan.There were no significant differences in dose to D90 or D98 of the high-risk clinical target volume with MRI vs. MRI-CT planning. MRI vs. MRI-CT planning resulted in mean D0.1cc bladder of 8.8 ± 3.4 Gy vs. 8.5 ± 3.2 Gy (p = 0.29) and D2cc bladder of 6.2 ± 1.4 Gy vs. 6.0 ± 1.4 Gy (p = 0.33), respectively. Mean D0.1cc rectum was 5.7 ± 1.2 Gy vs. 5.3 ± 1.2 Gy (p = 0.03) and D2cc rectum 4.0 ± 0.8 Gy vs. 4.2 ± 1.0 Gy (p = 0.18), respectively. Mean D0.1cc sigmoid was 5.2 ± 1.3 Gy vs. 5.4 ± 1.6 Gy (p = 0.23) and D2cc sigmoid 3.9 ± 1.0 Gy vs. 4.0 ± 1.1 Gy (p = 0.18), respectively.There were no clinically significant dosimetric differences between the MRI and MRI-CT plans. This study demonstrates that cervical brachytherapy with a titanium applicator can be planned with MRI alone, which is now our clinical standard.
View details for DOI 10.1016/j.brachy.2018.05.010
View details for Web of Science ID 000444662900004
View details for PubMedID 29945764
Evaluation of Radiomics to Predict the Accuracy of Markerless Motion Tracking of Lung Tumors: A Preliminary Study
FRONTIERS IN ONCOLOGY
2018; 8: 292
Template-based matching algorithms are currently being considered for markerless motion tracking of lung tumors. These algorithms use tumor templates derived from the planning CT scan, and track the motion of the tumor on single energy fluoroscopic images obtained at the time of treatment. In cases where bone may obstruct the view of the tumor, dual energy fluoroscopy may be used to enhance soft tissue contrast. The goal of this study is to predict which tumors will have a high degree of accuracy for markerless motion tracking based on radiomic features obtained from the planning CT scan, using peak-to-sidelobe ratio (PSR) as a surrogate of tracking accuracy. In this study, CT imaging data of 8 lung cancer patients were obtained and analyzed through the open source IBEX program to generate 2,287 radiomic features. Agglomerative hierarchical clustering was used to narrow down these features into 145 clusters comprised of the highest correlation to PSR. The features among the clusters with the least inter-correlation were then chosen to limit redundancy in the data. The results of this study demonstrated a number of radiomic features that are positively correlated to PSR. The features with the highest degree of correlation included complexity, orientation and range. This approach may be used to determine patients for whom markerless motion tracking would be beneficial.
View details for DOI 10.3389/fonc.2018.00292
View details for Web of Science ID 000440286400001
View details for PubMedID 30109215
View details for PubMedCentralID PMC6079207
Comparison of dosimetric and clinical outcomes between short- and long-channel cylinder applicators for vaginal brachytherapy in intermediate- and high-risk endometrial cancer
2018; 17 (4): 673–79
Vaginal brachytherapy (VBT) using a cylinder applicator is a standard treatment of intermediate- and high-risk endometrial cancer. We conducted a retrospective study of the dosimetric and clinical outcomes at our institution with 2 single-channel applicators in patients receiving VBT.One hundred thirty-six patients with endometrial cancer treated from 2006 to 2016 receiving VBT after definitive surgery were evaluated. Two cylinders were used with the distal dwell position 7.1-12.8 mm from the apex varying by diameter (short channel), and 3.2 mm from the apex (long channel). We prescribed 18-26 Gy in 3-4 fractions at 0.5 cm depth. Measurements of the distance from the apex to the prescription isodose line were taken from CT imaging. Student's t test and the Wilcoxon rank-sum test were used with corrections for multiple comparisons.Patients had International Federation of Gynecology and Obstetrics 2009 Stage I-II disease (70 Stage IA, 58 Stage IB, 9 Stage II). Mean cylinder apex dose was 95.2% and 154.7% of prescription (p < 0.001), and mean distance from apex to the prescription isodose line was 0.54 mm and 3.5 mm (p < 0.001) for the short- and long-channel cylinders, respectively. There were no significant differences in any toxicity between cylinders. Four patients (2.9%) had vaginal recurrence, all of whom were treated with the short-channel cylinder. Cylinder type was not associated with vaginal recurrence (p = 0.27).A cylinder applicator with a distal dwell position closer to the apex results in higher doses to the vaginal cuff and increased D2cc to the bladder. All four recurrences were in the short-channel cylinder. Additional investigation into applicator design and impact on patient outcomes in larger cohorts with sufficient followup is warranted.
View details for DOI 10.1016/j.brachy.2018.04.003
View details for Web of Science ID 000437819000005
View details for PubMedID 29759329
Decreased Risk of Radiation Pneumonitis With Coincident Concurrent Use of Angiotensin-converting Enzyme Inhibitors in Patients Receiving Lung Stereotactic Body Radiation Therapy
AMERICAN JOURNAL OF CLINICAL ONCOLOGY-CANCER CLINICAL TRIALS
2018; 41 (6): 576–80
Angiotensin-converting enzyme inhibitors (ACEi) have demonstrated decreased rates of radiation-induced lung injury in animal models and clinical reports have demonstrated decreased pneumonitis in the setting of conventionally fractionated radiation to the lung. We tested the role of ACEi in diminishing rates of symptomatic (grade ≥2) pneumonitis in the setting of lung stereotactic body radiation therapy (SBRT).We analyzed patients treated with thoracic SBRT to 48 to 60 Gy in 4 to 5 fractions from 2006 to 2014. We reviewed pretreatment and posttreatment medication profiles to document use of ACEi, angiotensin receptor blockers, bronchodilators, aspirin, PDE-5 inhibitors, nitrates, and endothelin receptor antagonists. Pneumonitis was graded posttreatment based on Common Terminology Criteria for Adverse Events Version 4.0. Univariate and multivariate analysis was performed and time to development of pneumonitis was evaluated by the Kaplan-Meier method.A total of 189 patients were evaluated with a median follow-up of 24.8 months. The overall 1-year rate of symptomatic pneumonitis was 13.2%. The 1-year rate of symptomatic pneumonitis was 4.2% for ACEi users versus 16.3% in nonusers (P=0.03). On univariate analysis, the odds of developing grade 2 or greater pneumonitis were significantly lower for patients on ACEi (P=0.03). On multivariate analysis, after controlling for clinicopathologic characteristics and dosimetric endpoints, there was a significant association between ACEi use and decreased risk of clinical pneumonitis (P=0.04). Angiotensin receptor blockers or other bronchoactive medications did not show significant associations with development of pneumonitis.Incidental concurrent use of ACEi demonstrated efficacy in diminishing rates of symptomatic pneumonitis in the setting of lung SBRT.
View details for DOI 10.1097/COC.0000000000000324
View details for Web of Science ID 000441384900009
View details for PubMedID 27560156
Providing MR Imaging for Cervical Cancer Brachytherapy: Lessons for Radiologists
RADIOLOGICAL SOC NORTH AMERICA. 2018: 932–44
Brachytherapy (BT), the use of a locally placed or implanted radioactive source for treatment of an adjacent tumor, is an important component in the treatment of patients with both early- and advanced-stage cervical cancer and is increasingly part of the standard treatment protocol. When it is feasible, many radiation oncologists choose to include a magnetic resonance (MR) imaging examination for planning BT treatment (ie, an MR imaging examination after placement of the applicator but before radiation dosing). MR imaging provides excellent soft-tissue contrast and allows radiation oncologists to individualize the radiation dose to the target volume and minimize the dose to adjacent organs that are at risk for radiation damage. However, traditionally, the radiology department has not performed imaging studies for planning, and the requirements are different compared with those of standard diagnostic imaging. In addition, many applicators are available for use in BT treatment of cervical cancer, and each must considered separately to determine MR safety and to define the best imaging parameters. Starting and supporting a robust gynecologic BT program includes implementing imaging protocols that are helpful to both radiation oncologists and diagnostic radiologists. By becoming more familiar with this treatment modality and the logistics of imaging patients undergoing BT, radiologists can provide imaging support for colleagues in the radiation oncology department and better care for patients. ©RSNA, 2018.
View details for DOI 10.1148/rg.2018170033
View details for Web of Science ID 000432395200019
View details for PubMedID 29757719
Association of conformality index and post-treatment radiation pneumonitis in early-stage non-small cell lung cancer treated with stereotactic body radiotherapy
JOURNAL OF RADIATION ONCOLOGY
2018; 7 (1): 63–67
View details for DOI 10.1007/s13566-018-0342-y
View details for Web of Science ID 000427760300008
A Medicare cost analysis of MRI- versus CT-based high-dose-rate brachytherapy of the cervix: Can MRI-based planning be less costly?
ELSEVIER SCIENCE INC. 2018: 326–33
While some institutions deliver multiple fractions per implant for MRI-based planning, it is common for only one fraction to be delivered per implant with CT-based cervical brachytherapy. The purpose of this study was to compare physician costs, hospital costs, and overall costs for cervical cancer patients treated with either CT-based or MRI-based high-dose-rate (HDR) cervical brachytherapy to determine if MRI-based brachytherapy as described can be financially feasible.We identified 40 consecutive patients treated with curative intent cervical brachytherapy. Twenty patients underwent CT-based HDR brachytherapy with five fractions delivered in five implants on nonconsecutive days in an outpatient setting with the first implant placed with a Smit sleeve under general anesthesia. Twenty patients received MRI-based HDR brachytherapy with four fractions delivered in two implants, each with MRI-based planning, performed 1-2 weeks apart with an overnight hospital admission for each implant. We used Medicare reimbursements to assess physician costs, hospital costs, and overall cost.The median cost of MRI-based brachytherapy was $14,248.75 (interquartile range [IQR]: $13,421.32-$15,539.74), making it less costly than CT-based brachytherapy with conscious sedation (i.e., $18,278.85; IQR: $17,323.13-$19,863.03, p < 0.0001) and CT-based brachytherapy with deep sedation induced by an anesthesiologist (i.e., $27,673.44; IQR: $26,935.14-$29,511.16, p < 0.0001). CT-based brachytherapy with conscious sedation was more costly than CT-based brachytherapy with deep sedation (p < 0.001).MRI-based brachytherapy using the described treatment course was less costly than both methods of CT-based brachytherapy. Cost does not need to be a barrier for MRI-based cervical brachytherapy, especially when delivering multiple fractions with the same application.
View details for DOI 10.1016/j.brachy.2017.11.020
View details for Web of Science ID 000427911400011
View details for PubMedID 29331574
Reduction of MRI signal distortion from titanium intracavitary brachytherapy applicator by optimizing pulse sequence parameters
2018; 17 (2): 377–82
To demonstrate that optimized pulse sequence parameters for a T2-weighted (T2w) fast spin echo acquisition reduced artifacts from a titanium brachytherapy applicator compared to conventional sequence parameters.Following Institutional Review Board approval and informed consent, seven patients were successfully imaged with both standard sagittal T2w fast spin echo parameters (voxel size of 0.98 × 0.78 × 4.0 mm3; readout bandwidth of 200 Hz/px; repetition time of 2800 ms; echo time of 91 ms; echo train length of 15; 36 slices; and imaging time of 3:16 min) and an additional optimized T2w sequence (voxel size of 0.98 × 0.98 × 4.0 mm3; readout bandwidth of 500 Hz/px; repetition time of 3610 ms; echo time of 91 ms; echo train length of 25; 18-36 slices; and imaging time of 1:15-2:30 min), which had demonstrated artifact reduction in prior phantom work. Visualized intracavitary tandem was hand-segmented by two of the authors. Three body imaging radiologists assessed image quality and intraobserver agreement scores were analyzed.The average segmented volume of the intracavitary applicator significantly (p < 0.05) decreased with the experimental pulse sequence parameters as compared to the standard pulse sequence. Comparison of experimental and standard T2w sequence qualitative scores for each reviewer showed no significant differences between the two techniques.This study demonstrated that pulse sequence parameter optimization can significantly reduce distortion artifact from titanium applicators while maintaining image quality and reasonable imaging times.
View details for DOI 10.1016/j.brachy.2017.10.013
View details for Web of Science ID 000427911400017
View details for PubMedID 29174384
Delineating the relationship between Point A prescription dose and pelvic lymph node doses in intracavitary high-dose-rate brachytherapy treatment of cervical cancer for use in low- and middle-income countries
2018; 17 (1): 201–7
To define the relationship between the Point A prescription dose and the dose delivered to various pelvic lymph node groups during high-dose-rate (HDR) brachytherapy treatment of cervical cancer. In less developed countries, brachytherapy is often done without three-dimensional image guidance, instead relying on plain radiography and prescription to Point A. A defined relationship between Point A dose and lymph node doses would help physicians in these health care settings to more accurately estimate nodal doses.Treatment data from 50 fractions of HDR brachytherapy of cervical cancer were reviewed, the pelvic lymph nodes were contoured, and dose-volume histogram parameters were obtained. Dose-volume histogram parameters for each contour were normalized as a percentage of the corresponding Point A dose. All nodal groups were divided into left and right sides, except the presacral nodal group.Mean Point A doses were bilateral (Bil) 5.92 Gy ± 0.58, left (L) 5.93 ± 0.59, and right (R) 5.92 ± 0.59. Mean normalized D90 values for the various lymph node groups were as follows-obturator: Bil 20.3% ± 4.5, L 20.5% ± 4.4, and R 20.2% ± 5.2; external iliac: Bil 9.5% ± 2.9, L 10.0% ± 3.1, and R 9.5% ± 3.0; internal iliac: Bil 12.2% ± 3.5, L 12.1% ± 3.4, and R 12.9% ± 4.7; common iliac: Bil 4.3% ± 1.6, L 4.3% ± 1.6, and R 4.3% ± 1.7; and presacral: 8.7% ± 3.4. These relationships can serve as a useful tool for evaluating lymph node doses during HDR brachytherapy of cervical cancer in facilities performing two-dimensional treatment planning and those with limited resources.
View details for DOI 10.1016/j.brachy.2017.09.003
View details for Web of Science ID 000424964700023
View details for PubMedID 29066085
Early outcomes and impact of a hybrid IC/IS applicator for a new MRI-based cervical brachytherapy program
2018; 17 (1): 187–93
The purpose of this study was to report early outcomes and assess the learning curve in a new MRI-based cervical brachytherapy program.We accrued 33 patients prospectively, and only patients with ≥3 months' followup (n = 27) were assessed for disease control and toxicity. Eras were defined as first half and second half for the intracavitary (IC)-only era (n = 13 each), and the intracavitary/interstitial (IC/IS) era was separated by difference in applicator availability (n = 7). Dose to 90% of the high-risk clinical target volume (D90 HR-CTV) and minimum dose to the maximally irradiated 2 cubic centimeters (D2cc) to organs at risk were used to assess dosimetry. Statistics were performed with t tests and Kaplan-Meier method.Median followup was 14.7 months. Median treatment duration was 50.5 vs. 57 days for patients treated with external beam radiation therapy at our institution vs. an outside institution (p = 0.03). One-year local control, noncervical pelvic control, distant metastasis-free rate, and overall survival were 84.0%, 96.0%, 78.5%, and 91.3%, respectively. When comparing the first half and second half eras of IC only, there were no differences in median D90 HR-CTV or D2cc of the bladder, rectum, or sigmoid. Comparing the entire IC era to the IC/IS era, median D90 HR-CTV trended higher from 88.0 Gy to 92.9 Gy (p = 0.11). D2cc rectum decreased from 69.3 Gy to 62.6 Gy (p = 0.01), and D2cc bladder trended lower from 87.5 Gy to 83.6 Gy (p = 0.09).There was no significant difference between the first half and second half eras with IC-only MRI-based brachytherapy. Incorporation of an IC/IS applicator generated the greatest dosimetric improvement. Early results of the MRI-based brachytherapy program are favorable.
View details for DOI 10.1016/j.brachy.2017.09.010
View details for Web of Science ID 000424964700021
View details for PubMedID 29089277
Evaluation of Deformable Image Registration-Based Contour Propagation From Planning CT to Cone-Beam CT
TECHNOLOGY IN CANCER RESEARCH & TREATMENT
2017; 16 (6): 801–10
View details for DOI 10.1177/1533034617697242
View details for Web of Science ID 000418867900017
Spectral characterization of tissues in high spectral and spatial resolution MR images: Implications for a classification-based synthetic CT algorithm
2017; 44 (5): 1865–75
To characterize the spectral parameters of tissues with high spectral and spatial resolution magnetic resonance images to be used as a foundation for a classification-based synthetic CT algorithm.A phantom was constructed consisting of a section of fresh beef leg with bone embedded in 1% agarose gel. The high spectral and spatial (HiSS) resolution MR imaging sequence used had 1.0 mm in-plane resolution and 11.1 Hz spectral resolution. This sequence was used to image the phantom and one patient. Post-processing was performed off-line with IDL and included Fourier transformation of the time-domain data, labeling of fat and water peaks, and fitting the magnitude spectra with Lorentzian functions. Images of the peak height and peak integral of both the water and fat resonances were generated and analyzed. Several regions-of-interest (ROIs) were identified in phantom: bone marrow, cortical bone, adipose tissue, muscle, agar gel, and air; in the patient, no agar gel was present but an ROI of saline in the bladder was analyzed. All spectra were normalized by the noise within each voxel; thus, all parameters are reported in terms of signal-to-noise (SNR). The distributions of tissue spectral parameters were analyzed and scatterplots generated. Water peak height in cortical bone was compared to air using a nonparametric t-test. Composition of the various ROIs in terms of water, fat, or fat and water was also reported.In phantom, the scatterplot of peak height (water versus fat) showed good separation of bone marrow and adipose tissue. Water versus fat integral scatterplot showed better separation of muscle and cortical bone than the peak height scatterplot. In the patient data, the distributions of water and fat peak heights were similar to that in phantom, with more overlap of bone marrow and cortical bone than observed in phantom. The relationship between bone marrow and cortical bone for peak integral was better separated than those of peak heights in the patient data. For both the phantom and patient, there was a significant amount of overlap in spectral parameters of cortical bone versus air.These results show promising results for utilizing HiSS imaging in a classification-based synthetic CT algorithm. Cortical bone and air overlap was expected due to the short T2* of bone; reducing early echo times would improve the SNR in bone and image data from these early echoes could help differentiate these tissue types. Further studies need to be done with the goal of better separation of air and bone, and to extend the concept to volumetric imaging before it can be clinically applied.
View details for DOI 10.1002/mp.12173
View details for Web of Science ID 000401154000025
View details for PubMedID 28236649
Clinical Application of a Hybrid RapidArc Radiotherapy Technique for Locally Advanced Lung Cancer
TECHNOLOGY IN CANCER RESEARCH & TREATMENT
2017; 16 (2): 224–30
Radiation treatment planning for locally advanced lung cancer can be technically challenging, as delivery of ≥60 Gy to large volumes with concurrent chemotherapy is often associated with significant risk of normal tissue toxicity. We clinically implemented a novel hybrid RapidArc technique in patients with lung cancer and compared these plans with 3-dimensional conformal radiotherapy and RapidArc-only plans.Hybrid RapidArc was used to treat 11 patients with locally advanced lung cancer having bulky mediastinal adenopathy. All 11 patients received concurrent chemotherapy. All underwent a 4-dimensional computed tomography planning scan. Hybrid RapidArc plans concurrently combined static (60%) and RapidArc (40%) beams. All cases were replanned using 3- to 5-field 3-dimensional conformal radiotherapy and RapidArc technique as controls.Significant reductions in dose were observed in hybrid RapidArc plans compared to 3-dimensional conformal radiotherapy plans for total lung V20 and mean (-2% and -0.6 Gy); contralateral lung mean (-2.92 Gy); and esophagus V60 and mean (-16.0% and -2.2 Gy; all P < .05). Contralateral lung doses were significantly lower for hybrid RapidArc plans compared to RapidArc-only plans (all P < .05). Compared to 3-dimensional conformal radiotherapy, heart V60 and mean dose were significantly improved with hybrid RapidArc (3% vs 5%, P = .04 and 16.32 Gy vs 16.65 Gy, P = .03). However, heart V40 and V45 and maximum spinal cord dose were significantly lower with RapidArc plans compared to hybrid RapidArc plans. Conformity and homogeneity were significantly better with hybrid RapidArc plans compared to 3-dimensional conformal radiotherapy plans ( P < .05). Treatment was well tolerated, with no grade 3+ toxicities.To our knowledge, this is the first report on the clinical application of hybrid RapidArc in patients with locally advanced lung cancer. Hybrid RapidArc permitted safe delivery of 60 to 66 Gy to large lung tumors with concurrent chemotherapy and demonstrated advantages for reduction in low-dose lung volumes, esophageal dose, and mean heart dose.
View details for DOI 10.1177/1533034616670273
View details for Web of Science ID 000396203300011
View details for PubMedID 27680023
View details for PubMedCentralID PMC5616034
Adaptive Radiotherapy for Head and Neck Cancer: Implications for Clinical and Dosimetry Outcomes
TECHNOLOGY IN CANCER RESEARCH & TREATMENT
2017; 16 (2): 218–23
To investigate the effects of adaptive radiotherapy on dosimetric, clinical, and toxicity outcomes for patients with head and neck cancer undergoing chemoradiotherapy with intensity-modulated radiotherapy.Fifty-one patients with advanced head and neck cancer underwent definitive chemoradiotherapy with the original plan optimized to deliver 70.2 Gy. All patients were resimulated at a median dose of 37.8 Gy (range, 27.0-48.6 Gy) due to changes in tumor volume and/or patient weight loss (>15% from baseline). Thirty-four patients underwent adaptive replanning for their boost planning (21.6 Gy). The dosimetric effects of the adaptive plan were compared to the original plan and the original plan copied on rescan computed tomography. Acute and late toxicities and tumor local control were assessed. Gross tumor volume reduction rate was calculated.With adaptive replanning, the maximum dose to the spinal cord, brain stem, mean ipsilateral, and contralateral parotid had a median reduction of -4.5%, -3.0%, -6.2%, and -2.5%, respectively (median of 34 patients). Median gross tumor volume and boost planning target volume coverage improved by 0.8% and 0.5%, respectively. With a median follow-up time of 17.6 months, median disease-free survival and overall survival was 14.8 and 21.1 months, respectively. Median tumor volume reduction rate was 35.2%. For patients with tumor volume reduction rate ≤35.2%, median disease-free survival was 8.7 months, whereas it was 16.9 months for tumor volume reduction rate >35.2%. Four patients had residual disease after chemoradiotherapy, whereas 64.7% (20 of 34) of patients achieved locoregional control.Implementation of adaptive radiotherapy in head and neck cancer offers benefits including improvement in tumor coverage and decrease in dose to organs at risk. The tumor volume reduction rate during treatment was significantly correlated with disease-free survival and overall survival.
View details for DOI 10.1177/1533034616662165
View details for Web of Science ID 000396203300010
View details for PubMedID 27502958
View details for PubMedCentralID PMC5616033
How one institution overcame the challenges to start an MRI-based brachytherapy program for cervical cancer
JOURNAL OF CONTEMPORARY BRACHYTHERAPY
2017; 9 (2): 177–86
Adaptive magnetic resonance imaging (MRI)-based brachytherapy results in improved local control and decreased high-grade toxicities compared to historical controls. Incorporating MRI into the workflow of a department can be a major challenge when initiating an MRI-based brachytherapy program. This project aims to describe the goals, challenges, and solutions when initiating an MRI-based cervical cancer brachytherapy program at our institution.We describe the 6-month multi-disciplinary planning phase to initiate an MRI-based brachytherapy program. We describe the specific challenges that were encountered prior to treating our first patient.We describe the solutions that were realized and executed to solve the challenges that we faced to establish our MRI-based brachytherapy program. We emphasize detailed coordination of care, planning, and communication to make the workflow feasible. We detail the imaging and radiation physics solutions to safely deliver MRI-based brachytherapy. The focus of these efforts is always on the delivery of optimal, state of the art patient care and treatment delivery within the context of our available institutional resources.Previous publications have supported a transition to MRI-based brachytherapy, and this can be safely and efficiently accomplished as described in this manuscript.
View details for DOI 10.5114/jcb.2017.66892
View details for Web of Science ID 000401601300013
View details for PubMedID 28533808
View details for PubMedCentralID PMC5437078
A novel surrogate to identify anatomical changes during radiotherapy of head and neck cancer patients
2017; 44 (3): 924–34
To develop a novel method to monitor external anatomical changes in head and neck cancer patients in order to triage possible adaptive radiotherapy needs.The presented approach aims to provide information on internal anatomical changes based on variations observed in external anatomy. Setup Cone Beam Computed Tomography (CBCT) images are processed to produce an accurate external contour of the patient's skin. After registering the CBCTs to the reference planning CT, the external contours from each CBCT are transferred to the initial - first week - CBCT. Contour radii, defined as the distances between an external contour and the isocenter projection in each CBCT slice, are calculated for each scan over the full 360 degrees. The changes in external anatomy are then quantified by the difference in radial distance between the external contours of any secondary CBCT relative to the initial CBCT. Finally, the radial difference is displayed in cylindrical coordinates as a 2D intensity map to highlight regions of interests with significant changes. Weekly CBCT scans from 15 head and neck patients were retrospectively analyzed to demonstrate the utility of this approach as a proof of principle. External changes suggested by the 2D radial difference map of an example patient after 23 fractions were then correlated with the changes in the gross tumor volumes and organs at risks. The resulting dosimetric effects were evaluated. An interactive standalone software application has been developed to facilitate the generation and the interpretation of the 2D intensity map.The 2D radial difference maps provided qualitative and quantitative information, such as the location and the magnitude of external contour changes and the rate at which these deviations occur. Out of the 15 patients, 10 presented clear evidence of general external volume shrinkage due to weight loss, and nine patients had at least one site of local shrinkage. Only two patients showed no signs of anatomical change during their entire treatment course. For the example patient, the mean (±σ) radial difference was 6.7 (±3.0) mm for the left parotid and 7.3 (±2.5) mm for the right parotid. The mean dose to the left and right parotids increased from 20.1 Gy to 30 Gy and from 16.3 Gy to 29.6 Gy, respectively.This novel method provides an efficient tool to visualize 3D external anatomical changes on a single 2D map. It quickly pinpoints the location of differences in anatomy during the course of radiotherapy, which can help physicians determine if a treatment plan needs to be adapted. The interactive graphic user interface developed in this study will be evaluated in an adaptive radiotherapy workflow for head and neck patients in a future prospective trial.
View details for DOI 10.1002/mp.12067
View details for Web of Science ID 000397870800013
View details for PubMedID 28019647
Improving the Accessibility of Patient Care Through Integration of the Hospital and Radiation Oncology Electronic Health Records
JCO CLINICAL CANCER INFORMATICS
2017; 1: 1–8
Radiation therapy (RT)-specific aspects of a patient's cancer care commonly are documented and scheduled through a radiation oncology electronic health record (rEHR). However, patients who receive RT also receive multidisciplinary care from providers who use the hospital EHR (hEHR). We created an electronic interface to integrate our hEHR and rEHR to improve communication of the RT aspects of care between our department and the rest of the hospital. The objective of this study was to assess the impact of rEHR and hEHR integration on the accessibility of the RT-specific aspects of patient care to providers.We performed a preintegration and postintegration survey of 175 staff members at our academic cancer center. Respondents rated the importance and accessibility of several RT encounters and documents on a Likert scale. The Wilcoxon-Mann-Whitney, χ2, and Fisher's exact tests were used to compare preintegration and postintegration responses.There were 32 and 19 responses to the pre- and postintegration surveys, respectively. rEHR items most commonly reported to be at least moderately important were the dates of first treatment (n = 29 [91%]), last treatment (n = 29 [91%]), brachytherapy (n = 22 [69%]), radiosurgery (n = 22 [69%]), and computed tomography simulation (n = 21 [66%]). A drastic improvement was found in most items made visible in the hEHR through the interface.By integrating our hEHR and rEHR, we improved the communication of patient care between the RT department and the multidisciplinary team. Institutions should pursue and support integration of the EHRs to improve the quality of care provided to patients with cancer.
View details for DOI 10.1200/CCI.17.00063
View details for Web of Science ID 000462301600033
View details for PubMedID 30657394
Metal Artifact Reduction in Cone-Beam Computed Tomography for Head and Neck Radiotherapy
TECHNOLOGY IN CANCER RESEARCH & TREATMENT
2016; 15 (6): NP88–NP94
To evaluate a method for reducing metal artifacts, arising from dental fillings, on cone-beam computed tomography images.A projection interpolation algorithm is applied to cone-beam computed tomography images containing metal artifacts from dental fillings. This technique involves identifying metal regions in individual cone-beam computed tomography projections and interpolating the surrounding values to remove the metal from the projection data. Axial cone-beam computed tomography images are then reconstructed, resulting in a reduction in the streak artifacts produced by the metal. Both phantom and patient imaging data are used to evaluate this technique.The interpolation substitution technique successfully reduced metal artifacts in all cases. Corrected images had fewer or no streak artifacts compared to their noncorrected counterparts. Quantitatively, regions of interest containing the artifacts showed reduced variance in the corrected images versus the uncorrected images. Average pixel values in regions of interest around the metal object were also closer in value to nonmetal regions after artifact reduction. Artifact correction tended to perform better on patient images with less complex metal objects versus those with multiple large dental fillings.The interpolation substitution is potentially an efficient and effective technique for reducing metal artifacts caused by dental fillings on cone-beam computed tomography image. This technique may be effective in reducing such artifacts in patients with head and neck cancer receiving daily image-guided radiotherapy.
View details for DOI 10.1177/1533034615618319
View details for Web of Science ID 000387759000010
View details for PubMedID 26614780
Observer Evaluation of a Metal Artifact Reduction Algorithm Applied to Head and Neck Cone Beam Computed Tomographic Images
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2016; 96 (4): 897–904
To quantify, through an observer study, the reduction in metal artifacts on cone beam computed tomographic (CBCT) images using a projection-interpolation algorithm, on images containing metal artifacts from dental fillings and implants in patients treated for head and neck (H&N) cancer.An interpolation-substitution algorithm was applied to H&N CBCT images containing metal artifacts from dental fillings and implants. Image quality with respect to metal artifacts was evaluated subjectively and objectively. First, 6 independent radiation oncologists were asked to rank randomly sorted blinded images (before and after metal artifact reduction) using a 5-point rating scale (1 = severe artifacts; 5 = no artifacts). Second, the standard deviation of different regions of interest (ROI) within each image was calculated and compared with the mean rating scores.The interpolation-substitution technique successfully reduced metal artifacts in 70% of the cases. From a total of 60 images from 15 H&N cancer patients undergoing image guided radiation therapy, the mean rating score on the uncorrected images was 2.3 ± 1.1, versus 3.3 ± 1.0 for the corrected images. The mean difference in ranking score between uncorrected and corrected images was 1.0 (95% confidence interval: 0.9-1.2, P<.05). The standard deviation of each ROI significantly decreased after artifact reduction (P<.01). Moreover, a negative correlation between the mean rating score for each image and the standard deviation of the oral cavity and bilateral cheeks was observed.The interpolation-substitution algorithm is efficient and effective for reducing metal artifacts caused by dental fillings and implants on CBCT images, as demonstrated by the statistically significant increase in observer image quality ranking and by the decrease in ROI standard deviation between uncorrected and corrected images.
View details for DOI 10.1016/j.ijrobp.2016.07.028
View details for Web of Science ID 000385524000023
View details for PubMedID 27788959
RECONSIDERING RADIORESISTANCE: LINAC-BASED STEREOTACTIC RADIOSURGERY FOR INTRACRANIAL METASTASES FROM MELANOMA AND RENAL CELL CARCINOMA
OXFORD UNIV PRESS INC. 2016: 181
View details for Web of Science ID 000398604104068
Examination of general cavity theory for magnesium and titanium doped lithium fluoride (TLD-100) of varying thicknesses in bone and lung
2016; 94: 1–7
View details for DOI 10.1016/j.radmeas.2016.08.005
View details for Web of Science ID 000389101800001
Predictors of post-treatment symptomatic pneumonitis in lung SBRT patients through decision tree analysis
JOURNAL OF RADIATION ONCOLOGY
2016; 5 (3): 273–78
View details for DOI 10.1007/s13566-016-0258-3
View details for Web of Science ID 000384324400006
Moving towards hospital and radiation oncology EMR integration: Results of an institutional survey.
AMER SOC CLINICAL ONCOLOGY. 2016
View details for DOI 10.1200/jco.2016.34.7_suppl.152
View details for Web of Science ID 000378109900149
Decision Trees Predicting Tumor Shrinkage for Head and Neck Cancer: Implications for Adaptive Radiotherapy
TECHNOLOGY IN CANCER RESEARCH & TREATMENT
2016; 15 (1): 139–45
To develop decision trees predicting for tumor volume reduction in patients with head and neck (H&N) cancer using pretreatment clinical and pathological parameters.Forty-eight patients treated with definitive concurrent chemoradiotherapy for squamous cell carcinoma of the nasopharynx, oropharynx, oral cavity, or hypopharynx were retrospectively analyzed. These patients were rescanned at a median dose of 37.8 Gy and replanned to account for anatomical changes. The percentages of gross tumor volume (GTV) change from initial to rescan computed tomography (CT; %GTVΔ) were calculated. Two decision trees were generated to correlate %GTVΔ in primary and nodal volumes with 14 characteristics including age, gender, Karnofsky performance status (KPS), site, human papilloma virus (HPV) status, tumor grade, primary tumor growth pattern (endophytic/exophytic), tumor/nodal/group stages, chemotherapy regimen, and primary, nodal, and total GTV volumes in the initial CT scan. The C4.5 Decision Tree induction algorithm was implemented.The median %GTVΔ for primary, nodal, and total GTVs was 26.8%, 43.0%, and 31.2%, respectively. Type of chemotherapy, age, primary tumor growth pattern, site, KPS, and HPV status were the most predictive parameters for primary %GTVΔ decision tree, whereas for nodal %GTVΔ, KPS, site, age, primary tumor growth pattern, initial primary GTV, and total GTV volumes were predictive. Both decision trees had an accuracy of 88%.There can be significant changes in primary and nodal tumor volumes during the course of H&N chemoradiotherapy. Considering the proposed decision trees, radiation oncologists can select patients predicted to have high %GTVΔ, who would theoretically gain the most benefit from adaptive radiotherapy, in order to better use limited clinical resources.
View details for DOI 10.1177/1533034615572638
View details for Web of Science ID 000369974200017
View details for PubMedID 25731804
Evaluation of a template-based algorithm for markerless lung tumour localization on single- and dual-energy kilovoltage images
BRITISH JOURNAL OF RADIOLOGY
2016; 89 (1068): 20160648
To evaluate a template-based matching algorithm on single-energy (SE) and dual-energy (DE) radiographs for markerless localization of lung tumours.A total of 74 images from 17 patients with Stages IA-IV lung cancer were considered. At the time of radiotherapy treatment, gated end-expiration SE radiographs were obtained at 60 and 120 kVp at different gantry angles (33° anterior and 41° oblique), from which soft-tissue-enhanced DE images were created. A template-based matching algorithm was used to localize individual tumours on both SE and DE radiographs. Tumour centroid co-ordinates obtained from the template-matching software on both SE and DE images were compared with co-ordinates defined by physicians.The template-based matching algorithm was able to successfully localize the gross tumor volume within 5 mm on 70% (52/74) of the SE images vs 91% (66/74) of the DE images (p < 0.01). The mean vector differences between the co-ordinates of the template matched by the algorithm and the co-ordinates of the physician-defined ground truth were 3.2 ± 2.8 mm for SE images vs 2.3 ± 1.7 mm for DE images (p = 0.03).Template-based matching on DE images was more accurate and precise than using SE images. Advances in knowledge: This represents, to the authors' knowledge, the largest study evaluating template matching on clinical SE and DE images, considering not only anterior gantry angles but also oblique angles, suggesting a novel lung tumour matching technique using DE subtraction that is reliable, accurate and precise.
View details for DOI 10.1259/bjr.20160648
View details for Web of Science ID 000389345900014
View details for PubMedID 27730838
View details for PubMedCentralID PMC5604930
Bladder distension improves the dosimetry of organs at risk during intracavitary cervical high-dose-rate brachytherapy
2016; 15 (1): 30–34
To evaluate dose-volume histograms (DVHs) and dose-surface histograms (DSHs) to analyze bladder distension during cervical brachytherapy.Twenty brachytherapy fractions from five cervical cancer patients were selected. For each fraction, empty and full (200cc of contrasted saline) bladder simulation CT scans existed, one of which was used to plan treatment. An alternative plan was then created with the unused scan. DVH for each fraction was generated for the bladder, rectum, sigmoid colon, and small bowel. Mean DVH dose, D0.1cc, and D2cc were calculated for each organ at risk. Plans were then exported to a MATLAB-based program to generate a DSH.Full bladder plans showed no difference in bladder D2cc or D0.1cc compared with empty bladder plans; however, bladder mean DVH dose and DSH dose were both significantly reduced. Full bladder plans showed a significant reduction in small intestine D2cc from 2.81 Gy to 1.83 Gy and reduction in D0.1cc from 4.07 Gy to 2.57 Gy (p < 0.05); similarly, sigmoid D2cc was significantly reduced from 4.24 Gy to 3.87 Gy (p < 0.05) and D0.1cc was reduced from 6.12 Gy to 5.61 Gy (p < 0.05) in full bladder plans. Both small intestine and sigmoid also showed reduced mean DVH and DSH dose in full bladder plans. The rectum showed no significant difference in D2cc, D0.1cc, mean DVH, or DSH dose between plans.Bladder distension during cervical brachytherapy significantly reduced dose in all DVH and DSH parameters for sigmoid and small intestine with no change in bladder parameters. It reduces dose to organ at risk, but the correlation to toxicity requires further investigation.
View details for DOI 10.1016/j.brachy.2015.09.009
View details for Web of Science ID 000369779000004
View details for PubMedID 26521661
A survey on table tolerances and couch overrides in radiotherapy
JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS
2016; 17 (6): 405–20
The purpose of this study was to survey current departmental policies on treatment couch overrides and the values of table tolerances used clinically. A 25-question electronic survey on couch overrides and tolerances was sent to full members of the American Association of Physicists in Medicine (AAPM). The first part of the survey asked participants if table overrides were allowed at their institution, who was allowed to perform these overrides, and if imaging was required with overrides. The second part of the survey asked individuals to provide table tolerance data for the following treatment sites: brain/head and neck (H&N), lung, breast, abdo-men/pelvis and prostate. Each site was further divided into IMRT/VMAT and 3D conformal techniques. Spaces for free-text were provided, allowing respondents to enter any table tolerance data they were unable to specify under the treatment sites listed. A total of 361 individuals responded, of which approximately half partici-pated in the couch tolerances portion of the survey. Overall, 86% of respondents' institutions allow couch tolerance overrides at treatment. Therapists were the most common staff members permitted to perform overrides, followed by physicists, dosimetrists, and physicians, respectively. Of the institutions allowing overrides, 34% reported overriding daily. More than half of the centers document the over-ride and/or require a setup image to radiographically verify the treatment site. With respect to table tolerances, SRS/SBRT table tolerances were the tightest, while clinical setup table tolerances were the largest. There were minimal statistically significant differences between IMRT/VMAT and 3D conformal table tolerances. Our results demonstrated that table overrides are relatively common in radiotherapy despite being a potential safety concern. Institutions should review their override policy and table tolerance values in light of the practices of other institutions. Careful attention to these matters is crucial in ensuring the safe and accurate delivery of radiotherapy.
View details for DOI 10.1120/jacmp.v17i6.6261
View details for Web of Science ID 000388927500036
View details for PubMedID 27929512
View details for PubMedCentralID PMC5690513
Leukemia Cutis of the Face, Scalp, and Neck Treated with Non-coplanar Split Field Volumetric Modulated Arc Therapy: A Case Report
2015; 7 (12): e430
Malignancies with a superficial involvement of the scalp present a unique technical challenge for radiation treatment planning. As an example of this, leukemic infiltration of the superficial skin as the only presentation of the disease is a rare entity. For such cases, radiation oncologists have typically treated with 3D conformal radiotherapy with matched electron fields, a technique that can lead to significant dose inhomogeneity. In this report, we describe the case of a patient with leukemia cutis with a superficial involvement of the scalp, face, and shoulders that was treated with volumetric modulated arc radiotherapy, with an impressive clinical response.
View details for DOI 10.7759/cureus.430
View details for Web of Science ID 000453608700038
View details for PubMedID 26848419
View details for PubMedCentralID PMC4727940
A multi-institutional study to assess adherence to lung stereotactic body radiotherapy planning goals
2015; 42 (8): 4629–35
A multi-institutional planning study was performed to evaluate the frequency that current guidelines established by Radiation Therapy Oncology Group (RTOG) protocols and other literature for lung stereotactic body radiotherapy (SBRT) treatments are followed.A total of 300 patients receiving lung SBRT treatments in four different institutions were retrospectively reviewed. The treatments were delivered using Linac based SBRT (160 patients) or image guided robotic radiosurgery (140). Most tumors were located peripherally (250/300). Median fractional doses and ranges were 18 Gy (8-20 Gy), 12 Gy (6-15 Gy), and 10 Gy (5-12 Gy) for three, four, and five fraction treatments, respectively. The following planning criteria derived from RTOG trials and the literature were used to evaluate the treatment plans: planning target volumes, PTVV 100 ≥ 95% and PTVV 95 ≥ 99%; conformality indices, CI100% < 1.2 and CI50% range of 2.9-5.9 dependent on PTV; total lung-ITV: V20Gy < 10%, V12.5Gy < 15%, and V5Gy < 37%; contralateral lung V5Gy < 26%; and maximum doses for spinal cord, esophagus, trachea/bronchus, and heart and great vessels. Populations were grouped by number of fractions, and dosimetric criteria satisfaction rates (CSRs) were reported.Five fraction regimens were the most common lung SBRT fractionation (46%). The median PTV was 27.2 cm(3) (range: 3.8-419.5 cm(3)). For all plans: mean PTVV 100 was 94.5% (±5.6%, planning CSR: 69.8%), mean PTVV 95 was 98.1% (±4.1%, CSR: 69.5%), mean CI100% was 1.14 (±0.21, CSR: 79.1%, and 16.5% within minor deviation), and mean CI50% was 5.63 (±2.8, CSR: 33.0%, and 28.0% within minor deviation). When comparing plans based on location, peripherally located tumors displayed higher PTVV 100 and PTVV 95 CSR (71.5% and 71.9%, respectively) than centrally located tumors (61.2% and 57.1%, respectively). Overall, the planning criteria were met for all the critical structure such as lung, heart, spinal cord, esophagus, and trachea/bronchus for at least 85% of the patients.Among the various parameters that were used to evaluate the SBRT plans, the CI100% and CI50% were the most challenging criteria to meet. Although the CSRs of organs at risk were higher among all cases, their proximity to the PTV was a significant factor.
View details for DOI 10.1118/1.4926551
View details for Web of Science ID 000358933000020
View details for PubMedID 26233190
Markerless motion tracking of lung tumors using dual-energy fluoroscopy
2015; 42 (1): 254–62
To evaluate the efficacy of dual-energy (DE) vs single-energy (SE) fluoroscopic imaging of lung tumors using a markerless template-based tracking algorithm.Ten representative patient breathing patterns were programmed into a Quasar™ motion phantom. The phantom was modified by affixing pork ribs to the surface, and a cedar insert with a small spherical volume was used to simulate lung and tumor, respectively. Sequential 60 kVp (6 mA) and 120 kVp (1.5 mA) fluoroscopic sequences were acquired. Frame-by-frame weighted logarithmic subtraction was performed resulting in a DE fluoroscopic sequence. A template-based algorithm was then used to track tumor motion throughout the DE and SE fluoroscopy sequences. Tracking coordinates were evaluated against ground-truth tumor locations. Fluoroscopic images were also acquired for two lung cancer patients, neither of which had implanted fiducials.For phantom imaging, a total of 1925 frames were analyzed. The algorithm successfully tracked the target on 99.9% (1923/1925) of DE frames vs 90.7% (1745/1925) SE images (p < 0.01). The displacement between tracking coordinates and ground truth for the phantom was 1.4 mm ± 1.1 mm for DE vs 2.0 mm ± 1.3 mm for SE (p < 0.01). Images from two patients, one with a larger tumor and one with a smaller tumor, were also analyzed. For the patient with the larger tumor, the average displacement from physician defined ground truth was 1.2 mm ± 0.6 mm for DE vs 1.4 mm ± 0.7 mm for SE (p = 0.016). For the patient that presented with a smaller tumor, the average displacement from physician defined ground truth was 2.2 mm ± 1.0 mm for DE vs 3.2 mm ± 1.4 mm for SE (p < 0.01). Importantly, for this single patient with the smaller tumor, 15.6% of the SE frames had >5 mm displacements from the ground truth vs 0% for DE fluoroscopy.This work indicates the potential for markerless tumor tracking utilizing DE fluoroscopy. With DE imaging, the algorithm showed improved detectability vs SE fluoroscopy and was able to accurately track the tumor in nearly all cases.
View details for DOI 10.1118/1.4903892
View details for Web of Science ID 000347957200024
View details for PubMedID 25563265
JUDICIOUS USE OF RADIOSURGERY (SRS) MAY CHANGE THE ULTIMATE PATTERNS OF FAILURE IN PATIENTS WITH BRAIN METASTASIS FROM MELANOMA
OXFORD UNIV PRESS INC. 2013: 186
View details for Web of Science ID 000327456200730
INTRACRANIAL CONTROL OF RENAL CELL CARCINOMA BRAIN METASTASIS USING LINAC BASED STEREOTACTIC RADIOSURGERY
OXFORD UNIV PRESS INC. 2012: 141
View details for Web of Science ID 000310971300558
Verification of dose distribution for volumetric modulated arc therapy total marrow irradiation in a humanlike phantom
2012; 39 (1): 281–88
Volumetric modulated arc therapy (VMAT) treatment planning studies have been reported to provide good target coverage and organs at risk (OARs) sparing in total marrow irradiation (TMI). A comprehensive dosimetric study simulating the clinical situation as close as possible is a norm in radiotherapy before a technique can be used to treat a patient. Without such a study, it would be difficult to make a reliable and safe clinical transition especially with a technique as complicated as VMAT-TMI. To this end, the dosimetric feasibility of VMAT-TMI technique in terms of treatment planning, delivery efficiency, and the most importantly three dimensional dose distribution accuracy was investigated in this study. The VMAT-TMI dose distribution inside a humanlike Rando phantom was measured and compared to the dose calculated using RapidArc especially in the field junctions and the inhomogeneous tissues including the lungs, which is the dose-limiting organ in TMI.Three subplans with a total of nine arcs were used to treat the planning target volume (PTV), which was determined as all the bones plus the 3 mm margin. Thermoluminescent detectors (TLDs) were placed at 39 positions throughout the phantom. The measured TLD doses were compared to the calculated plan doses. Planar dose for each arc was verified using mapcheck.TLD readings demonstrated accurate dose delivery, with a median dose difference of 0.5% (range: -4.3% and 6.6%) from the calculated dose in the junctions and in the inhomogeneous medium including the lungs.The results from this study suggest that RapidArc VMAT technique is dosimetrically accurate, safe, and efficient in delivering TMI within clinically acceptable time frame.
View details for DOI 10.1118/1.3668055
View details for Web of Science ID 000298812200031
View details for PubMedID 22225298
Planning tools for modulated electron radiotherapy.
2010; 37 (5): 2215-24
To develop tools to plan modulated electron radiotherapy (MERT) and to compare the MERT plans to conventional or intensity modulated radiotherapy (IMRT) treatment plans.Monte Carlo dose calculations of electron fields shaped with the inherent photon multileaf collimators (MLCs) were investigated in this study. Treatment plans for four postmastectomy breast cancer patients were generated using MERT. The distances from the patient skin surfaces to the distal planning target volume surfaces were computed along the beam axis direction to determine the physical depth. Electron beam energies were selected to provide target coverage at these depths and energy bins were generated. A custom built MERT treatment planning graphical user interface (MERTgui) was used to shape the electron bins into deliverable electron segments. Monte Carlo dose distribution simulations were performed using the MLC-defined segments generated from the MERTgui. A custom built superposition gui was used to combine doses for each segment using relative weights and final MERT treatment plans were compared to the conventional or IMRT treatment plans. In addition, a demonstration of combined MERT and IMRT treatment plans was performed.The MERT treatment plans provided acceptable target organ coverage in all cases. Relative to 3D conventional or IMRT treatment plans, the MERT plans predicted lower heart doses in all cases; average of the heart D20 of all plans was reduced from 14.1 to 3.3 Gy. The contralateral breast and contralateral lung doses decreased substantially with MERT planning compared to IMRT (on average, contralateral breast heart D20 was reduced from 8.7 to 0.7 Gy and contralateral lung D20 was reduced from 8.4 to 1.2 Gy with MERT). Ipsilateral lung D20 was lower with MERT than with the conventional plans (44.6 vs 29.2 Gy with MERT), but greater when compared against IMRT treatment plans (25.4 vs 28.9 Gy with MERT). A MERT and IMRT combination plan was generated to benefit from the complementary advantages of MERT and IMRT, resulting in satisfactory target coverage and reduced organ at risk doses.MERT tools can facilitate treatment planning and provide plans for treatment of shallow targets such as the postmastectomy chest wall.
View details for DOI 10.1118/1.3395573
View details for PubMedID 20527555