Synchrotron X-ray boost delivered by Microbeam Radiation Therapy improves glioma control after conventional fractionated X-ray therapy

International audienceSynchrotron microbeam radiation therapy (MRT) is an alternative treatment modality for brain tumors which uses synchrotron light. MRT relies on the spatial fractionation of the incident X-rays which allows high dose delivery to tumors (hundreds of Gy in the microbeam paths) without severely damaging normal tissues. Because temporal fractionation is the standard clinical radiotherapy protocol for brain tumors, the aim of this work was to evaluate the efficiency of MRT delivered as a boost after a temporally fractionated broad beam (BB) irradiation sequence to palliate F98 intracerebral glioma bearing rats. Rats were treated by 3 temporally fractionated BB irradiations at 6 Gy, then by 2 temporally fractionated synchrotron irradiations in the BB or in the MRT mode at 8 Gy. In vivo tumor follow up was performed by MRI. Ex vivo cell cycle analysis was made by FACS; tissue responses were characterized histopathologically.MRT induced a significant and prolonged tumor cell cycle arrest compared with BB exposures. MRT stopped the tumor growth during 4 weeks and significantly increased the median survival time compared with the BB group. These results show for the first time the relevance of MRT as a radiation boost delivered after BB irradiation, suggesting that MRT is a realistic and more efficient alternative for brain tumor treatment in rats when applied in a hypo-fractionated schedule