LET dependency of human normal dermal cells survival in carbon ion irradiation

Yoshida, Yukari*; Mizohata, Kensuke*; Matsumura, Akihiko*; Isono, Mayu*; Yako, Tomoko*; Nakano, Takashi*; Funayama, Tomoo; Kobayashi, Yasuhiko; Kanai, Tatsuaki*

In the clinical application of carbon-ion (C-ion) radiation therapy in Japan, different RBE values of carbons have been used for clinical and biological endpoints. The biological RBE (bRBE) was estimated by a method that is based on the linear-quadratic (LQ) model, and was defined at the 10% surviving fraction of human salivary gland (HSG) tumor cells. However, many of biological parameters, that is, type of tissues, different sort of cells, oxygenation levels, and all, could affect radiosensitivity. Thus, normal human dermal fibroblasts (NHDF) cells were exposed to C-ion beams at Gunma University (10-80 keV/micrometer) and TIARA (108 and 158 keV/micrometer). The surviving fractions were analyzed with colony formation assays. The experimental RBE (eRBE) values were estimated from the radiation dose survival curve fitted by LQ model, and defined .