Synchrotron X-ray boost delivered by Microbeam Radiation Therapy after conventional X-ray therapy fractionated in time improves F98 glioma control

Abstract Purpose Synchrotron microbeam radiation therapy (MRT) is based on the spatial fractionation of the incident, highly collimated synchrotron beam into arrays of parallel microbeams depositing several hundred grays. It appears relevant to combine MRT with a conventional treatment course, preparing a treatment scheme for future patients in clinical trials. The efficiency of MRT delivered after several broad beam (BB) fractions to palliate of F98 brain tumors in rats in comparison with BB fractions alone was evaluated in this study. Materials/Methods Rats bearing 106 F98 cells implanted in the caudate nucleus were irradiated by 5 fractions in broad beam (BB) mode (3x6Gy + 2x8Gy BB) or by 2 boost fractions in MRT mode, of a total of 5 fractions (3x6Gy BB + MRT 2x8Gy valley dose; peak dose 181Gy (50/200μm)). Tumor growth was evaluated in vivo by MRI follow up at T-1, T7, T12 T15, T20, T25 days, after radiotherapy, and by histology and FACS studies. Results MRT-boosted tumors displayed lower cell density and cell proliferation compared with BB-irradiated tumors. The MRT boost completely stopped tumor growth during ∼4 weeks and led to a significant increase in MST, while tumors treated with BB alone recurred within few days after the last radiation fraction. Conclusions The first evidence is presented that MRT, delivered as a boost of a conventional fractionated irradiation by orthovoltage broad X-ray beams, is feasible and more efficient than a conventional radiotherapy alone.