SU‐F‐500‐10: Targeted Delivery of Microbeam Irradiation and Initial Mouse Brain Tumor Model Studies Using a Table Top MRT System

Purpose: Microbeam radiation therapy (MRT) is an experimental and preclinical radiotherapy method for cancer treatment that has been shown, in animal studies, to have the capability to selectively eradicate tumor without damaging normal tissue functions. The reliance of MRT on synchrotron radiation has prevented widespread research in this field and is a major roadblock for future clinical applications. Our goal is to develop a compact image‐guided MRT system based on high power distributed x‐ray source array and explore the radiobiology behind MRT using various mouse brain tumor models. Methods: We developed a novel protocol of combined MRI/x‐ray radiograph image‐guided MRT which enables irradiating two mice simultaneously. This protocol proceeds as follows: tumor localization with MRI, landmark identification with x‐ray projections, registration between the two images to determine the relative location of the tumor in the RT coordinate space, and treatment with the microbeam irradiator. We evaluated the targeting accuracy and tumor cell response of the protocol with U87 MG human glioma tumor bearing mice using γ‐H2AX staining. A survival study of U87 human glioma tumor bearing mice treated with three‐microbeam MRT (32Gy/beam) was carried out using this protocol. Results: The average targeting accuracy measured in the γ‐H2AX stained slices was about 280 μrn which is well below our beamwidth (350 μrn). In the survival study, U87 tumor mice treated using this MRT protocol showed an average survival time of 45 days, an extension of 6 days compared with 39 days in the control group. Conclusion: The initial tumor mice studies have demonstrated the feasibility of MRI/x‐ray radiograph guided MRT treatment in animal research. We believe this image‐guide MRT protocol could enable more efficient animal experiments with various brain tumor models to better understand MRT mechanisms.