LET and ion-species dependence for cell killing and mutation induction in normal human fibroblasts

We have been studying LET and ion species dependence of RBE values in cell killing and mutation induction. Normal human skin fibroblasts were irradiated with heavy-ion beams such as carbon (290MeV/u and 135MeV/u), neon (230MeV/u and 400MeV/u), silicon (490MeV/u) and iron (500MeV/u) ion beams, generated by Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences (NIRS). Cell killing effect was detected as reproductive cell death using a colony formation assay. Mutation induction in hprt locus was detected to measure 6-thioguanine resistant colonies. The RBE-LET curves of cell killing and mutation induction were different each ion beam. So, we plotted RBE for cell killing and mutation induction as function of Z*2/B2 instead of LET. RBE-Z*2/B2 curves of cell killing indicated that the discrepancy of RBE-LET curves was reconciled each ion species. But RBE-Z*2/B2 curves of mutation induction didn\u27t corresponded between carbon- and silicon-ion beams. These results suggested that different biological endpoints may be suitable for different physical parameter, which represent the track structure of energy deposition of ion beams