@misc{oai:repo.qst.go.jp:00069166,
 author = {Hirayama, Ryoichi and Ito, Atsushi and Kase, Yuuki and Ando, Koichi and Furusawa, Yoshiya and 平山 亮一 and 伊藤 敦 and 加瀬 優紀 and 安藤 興一 and 古澤 佳也},
 month = {Nov},
 note = {Biological effects of radiation come principally from damages on DNA. DNA damages by X-rays as well as heavy ions are induced by a combination of direct and indirect actions. To understand the contribution of indirect action in the effects of high LET radiations, we examined radioprotection by dimethylsulfoxide (DMSO), which is thought to suppress the indirect action, without affecting the direct one. Exponentially growing Chinese hamster V79 cells were exposed to low- or high LET radiations in the presence or absence of DMSO. Maximal protectable fraction was estimated from regression lines in the reciprocal plots of radical scavenger concentrations and the cell survivals. The contribution of indirect action decreased with increasing the LET, but was not reach to zero even at the very high LET. The contribution of indirect action in the cell killing was 32% at LET of 2106 keV/µm. Relative biologic effectiveness (RBE) is the dose ratio of X-rays to heavy ion to give the same biological effects, in which we used the doses to reduce the cell survivals to 0.1. RBE increased with LET, took a maximum at 200 keV/µm, and decreased thereafter with increasing LET. RBE of direct action for cell killing was higher than that of indirect action. We can conclude that the direct action takes major part in the RBE on high LET region, because a small change of RBE was observed through the indirect action., ASR2007},
 title = {Differential Contribution of Direct and Indirect Actions in Cell Killing by Low- and High LET Region},
 year = {2007}
}