Irradiation of intracerebral 9L gliosarcoma by a single array of microplanar x-ray beams from a synchrotron: balance between curing and sparing

The purpose of this work was the understanding of microbeam radiation therapy at the ESRF in order to find the best compromise between curing of tumors and sparing of normal tissues, to obtain a better understanding of survival curves and to report its efficiency. This method uses synchrotron-generated x-ray microbeams. Rats were implanted with 9L gliosarcomas and the tumors were diagnosed by MRI. They were irradiated 14 days after implantation by arrays of 25 μm wide microbeams in unidirectional mode, with a skin entrance dose of 625 Gy. The effect of using 200 or 100 μm center-to-center spacing between the microbeams was compared. The median survival time (post-implantation) was 40 and 67 days at 200 and 100 μm spacing, respectively. However, 72% of rats irradiated at 100 μm spacing showed abnormal clinical signs and weight patterns, whereas only 12% of rats were affected at 200 μm spacing. In parallel, histological lesions of the normal brain were found in the 100 μm series only. Although the increase in lifespan was equal to 273% and 102% for the 100 and 200 μm series, respectively, the 200 μm spacing protocol provides a better sparing of healthy tissue and may prove useful in combination with other radiation modalities or additional drugs.