High LET radiobiology at NIRS--current status and future plan.

HIMAC synchrotron radiates not only physical beams to cancer patients but also attractiveness to healthy scientists. Our persistent interest to clarify the biologically significant damage caused by high LET radiation needs multilayered approaches including molecular, cellular and tissue levels; all the levels being deeply integrated with physics. The outcome of our research is important for (1) promoting the evidence-based radiotherapy and (2) clarifying the radiation risk in space. We are currently conducting the following experiments; LET-RBE relationship for cell kills, chromatin damages and mutation induction, mitochondrial damages, brain damages at cellular and behavioral level, and fractionated irradiation to skin, gut and tumors. Capacity of cells to repair DNA damages may play an important role in space radiation environment that is characterized as a long-term exposure at low dose rates with mixed LET radiation. Experiments using cells deficient of DNA repair suggested that a process of damage recognition is critical for biological effectiveness of high LET radiation. Specific for space radiation research, we have started a long-term exposure of cultured cells to secondary beams produced at the HIMAC Biology Room. A future plan using HIMAC beams is described.