Enhanced Efficacy of Multiport Synchrotron Microbeam Radiation Therapy for Brain Tumors in Rats

Microbeam Radiation Therapy (MRT) is a drastically novel approach of radiosurgery, challenging the understanding of how normal tissues respond to radiation therapy, where X-rays generated by a synchrotron light source are collimated into wafers of high-dose (hundreds of Gray), thin (50 µm) parallel microbeams. Recent work showed that MRT dose prescription must consider a dual approach: separating normal tissue dose constraints tied to the valley dose prescription and anti-tumor effects, depending on the prescribed number of ports. Here, we consolidate this assumption by increasing the number of MRT incidences to irradiate 9L-bearing rats with a cumulated valley dose of 10 Gy. 9L-bearing rats were irradiated by eight ports of conventional Broad Beam (BB) or MRT. Animals were followed up clinically by MR imaging, histopathology and survival analysis. MRI follow-up revealed that MRT significantly amplified antitumor effect and tumor tissue damage while improving the clinical score of animals. Ten Gy, delivered by either BB or MRT, increased median survival time to 15 and 39.5 days after irradiation, respectively. Neither complete ablation of brain tumors nor long-term survival was achieved, but multiport MRT (eight ports) showed an outstanding dose equivalence factor (x2.9), which needs to be tested in a clinical environment.