Billy Loo, Postdoctoral Faculty Sponsor
FLASH Irradiation Results in Reduced Severe Skin Toxicity Compared to Conventional-Dose-Rate Irradiation.
Radiation therapy, along with surgery and chemotherapy, is one of the main treatments for cancer. While radiotherapy is highly effective in the treatment of localized tumors, its main limitation is its toxicity to normal tissue. Previous preclinical studies have reported that ultra-high dose-rate (FLASH) irradiation results in reduced toxicity to normal tissues while controlling tumor growth to a similar extent relative to conventional-dose-rate (CONV) irradiation. To our knowledge this is the first report of a dose-response study in mice comparing the effect of FLASH irradiation vs. CONV irradiation on skin toxicity. We found that FLASH irradiation results in both a lower incidence and lower severity of skin ulceration than CONV irradiation 8 weeks after single-fraction hemithoracic irradiation at high doses (30 and 40 Gy). Survival was also higher after FLASH hemithoracic irradiation (median survival >180 days at doses of 30 and 40 Gy) compared to CONV irradiation (median survival 100 and 52 days at 30 and 40 Gy, respectively). No ulceration was observed at doses 20 Gy or below in either FLASH or CONV. These results suggest a shifting of the dose-response curve for radiation-induced skin ulceration to the right for FLASH, compared to CONV irradiation, suggesting the potential for an enhanced therapeutic index for radiation therapy of cancer.
View details for DOI 10.1667/RADE-20-00090
View details for PubMedID 32853385
Evaluating the Reproducibility of Mouse Anatomy under Rotation in a Custom Immobilization Device for Conformal FLASH Radiotherapy.
The observation of an enhanced therapeutic index for FLASH radiotherapy in mice has created interest in practical laboratory-based FLASH irradiators. To date, systems capable of 3D conformal FLASH irradiation in mice have been lacking. We are developing such a system, incorporating a high-current linear accelerator to produce a collimated X-ray beam in a stationary beamline design, rotating the mouse about a longitudinal axis to achieve conformal irradiation from multiple beam directions. The purpose of this work was to evaluate the reproducibility of mouse anatomy under rotation at speeds compatible with conformal FLASH delivery. Three short-hair mice and two hairless mice were immobilized under anesthesia in body weight-specific contoured plastic molds, and subjected to three rotational (up to 3 revolutions/s) and two non-rotational movement interventions. MicroCT images were acquired before and after each intervention. The displacements of 11 anatomic landmarks were measured on the image pairs. The displacement of the anatomical landmarks with any of the interventions was 0.5 mm or less for 92.4% of measurements, with a single measurement out of 275 (11 landmarks × 5 interventions × 5 mice) reaching 1 mm. There was no significant difference in the displacements associated with rotation compared to those associated with moving the immobilized mouse in and out of a scanner or with leaving the mouse in place for 5 min with no motion. There were no significant differences in displacements between mice with or without hair, although the analysis is limited by small numbers, or between different anatomic landmarks. These results show that anatomic reproducibility under rotation speed corresponding to FLASH irradiation times appears to be compatible with conformal/stereotactic irradiation in mice.
View details for DOI 10.1667/RADE-20-00095
View details for PubMedID 32857849
A near-infrared phosphorescent nanoprobe enables quantitative, longitudinal imaging of tumor hypoxia dynamics during radiotherapy.
Hypoxia plays a key role in tumor resistance to radiotherapy (RT). It is important to study hypoxia dynamics during RT to improve treatment planning and prognosis. Here, we describe a luminescent nanoprobe, composed of a fluorescent semiconducting polymer and palladium (Pd) complex, for quantitative longitudinal imaging of tumor hypoxia dynamics during RT. The nanoprobe was designed to provide high sensitivity and reversible response for the subtle change in hypoxia over a narrow range (0-30 mmHg O2), which spans the oxygen range where tumors have limited radiosensitivity. Following intravenous administration, the nanoprobe efficiently accumulated in and distributed across the tumor, including the hypoxic region. The ratio between emissions at 700 and 800 nm provided quantitative mapping of hypoxia across the entire tumor. The nanoprobe has been applied to image the tumor hypoxia dynamics over 7 days during fractionated RT, revealing that high fractional dose (10 Gy) was more effective in improving tumor reoxygenation than low dose (2 Gy) and the effect tended to persist longer in smaller or more radiosensitive tumors. Our results also indicated the importance of the reoxygenation efficiency of the first fraction in the prediction of the radiation treatment outcome. In summary, this work has established a new nanoprobe for highly sensitive, quantitative and longitudinal imaging of tumor hypoxia dynamics following RT, and demonstrated its value for assessing the efficacy of RT and radiation treatment planning.
View details for DOI 10.1158/0008-5472.CAN-19-0530
View details for PubMedID 31311808
The role of granulocyte macrophage colony stimulating factor (GM-CSF) in radiation-induced tumor cell migration.
Clinical & experimental metastasis
Recently it has been observed in preclinical models that that radiation enhances the recruitment of circulating tumor cells to primary tumors, and results in tumor regrowth after treatment. This process may have implications for clinical radiotherapy, which improves control of a number of tumor types but which, despite continued dose escalation and aggressive fractionation, is unable to fully prevent local recurrences. By irradiating a single tumor within an animal bearing multiple lesions, we observed an increase in tumor cell migration to irradiated and unirradiated sites, suggesting a systemic component to this process. Previous work has identified the cytokine GM-CSF, produced by tumor cells following irradiation, as a key effector of this process. We evaluated the ability of systemic injections of a PEGylated form of GM-CSF to stimulate tumor cell migration. While increases in invasion and migration were observed for tumor cells in a transwell assay, we found that daily injections of PEG-GM-CSF to tumor-bearing animals did not increase migration of cells to tumors, despite the anticipated changes in circulating levels of granulocytes and monocytes produced by this treatment. Combination of PEG-GM-CSF treatment with radiation also did not increase tumor cell migration. These findings suggest that clinical use of GM-CSF to treat neutropenia in cancer patients will not have negative effects on the aggressiveness of residual cancer cells. However, further work is needed to characterize the mechanism by which GM-CSF facilitates systemic recruitment of trafficking tumor cells to tumors.
View details for PubMedID 29536224
Macrophages Promote Circulating Tumor Cell-Mediated Local Recurrence Following Radiation Therapy in Immunosuppressed Patients.
Although radiation therapy (RT) decreases the incidence of locoregional recurrence in breast cancer, patients with triple-negative breast cancer (TNBC) have increased risk of local recurrence following breast-conserving therapy (BCT). The relationship between RT and local recurrence is unknown. Here we tested the hypothesis that recurrence in some instances is due to the attraction of circulating tumor cells to irradiated tissues. To evaluate the effect of absolute lymphocyte count on local recurrence after RT in TNBC patients, we analyzed radiation effects on tumor and immune cell recruitment to tissues in an orthotopic breast cancer model. Recurrent patients exhibited a prolonged low absolute lymphocyte count when compared to non-recurrent patients following RT. Recruitment of tumor cells to irradiated normal tissues was enhanced in the absence of CD8+ T cells. Macrophages (CD11b+F480+) preceded tumor cell infiltration and were recruited to tissues following RT. Tumor cell recruitment was mitigated by inhibiting macrophage infiltration using maraviroc, an FDA-approved CCR5 receptor antagonist. Our work poses the intriguing possibility that excessive macrophage infiltration in the absence of lymphocytes promotes local recurrence after RT. This combination thus defines a high-risk group of TNBC patients.
View details for PubMedID 29880480