Enhancement of survival of 9L gliosarcoma bearing rats following intracerebral delivery of drugs in combination with microbeam radiation therapy

Microbeam radiation therapy (MRT) is a form of radiosurgery first dedicated to the treatment of brain tumors. It uses arrays of synchrotron generated X-rays microbeams of very high doses (typically 625 Gy). Microbeams are typically few micrometers large (25 μm) and few hundred micrometers spaced (200 μm). Previous experiments have shown that despite a good tumor eradication rate (5/11), a 100-μm spacing unidirectional irradiation (skin dose 625 Gy, width 25 μm) was too invasive for normal tissue. On the contrary, a 200-μm spacing unidirectional irradiation preserved healthy tissue with a low tumor eradication rate (2/32). The purpose of this study was to enhance the potential of the 200 μm spacing irradiation protocol. After diagnosis of the tumor by MRI, 9L tumor-bearing rats were laterally irradiated with 51 microbeams (625 Gy, 25 μm, 200 μm) 14 days after implantation. Three drugs (Gd-DTPA, CisPt, temozolomide) were tested, after intratumoral injection at the theoretical center of the tumor. Control rats displayed a median survival time of 19 days. There was no significant difference between drug-treated rats and control group. Irradiated animals showed an increase in life span (ILS) of 60.5%. Interestingly, the ILS increased to 131.6% and 1/6 rat survived more than 1 year in case of MRT combined with gadolinium injection. These results showed that the synergy between gadolinium injection (acting as a dose enhancer) and MRT improved significantly the life span of tumor bearing rats (more than a factor 2).