@misc{oai:repo.qst.go.jp:00070574,
 author = {Hirayama, Ryoichi and Matsumoto, Yoshitaka and Uzawa, Akiko and Takase, Nobuhiro and Tsuruoka, Chizuru and Wada, Mami and Noguchi, Miho and Kase, Yuki and Matsufuji, Naruhiro and Ito, Atsushi and Okayasu, Ryuichi and Furusawa, Yoshiya and 平山 亮一 and 松本 孔貴 and 鵜澤 玲子 and 鶴岡 千鶴 and 和田 麻美 and 松藤 成弘 and 伊藤 敦 and 岡安 隆一 and 古澤 佳也},
 month = {Sep},
 note = {The contribution of indirect action mediated by OH radicals in cell killing can be estimated from the maximum degree of protection by dimethylsulfoxide (DMSO), which suppresses indirect action of radiation without affecting direct action. Exponentially growing Chinese hamster ovary cells under oxic and hypoxic conditions were exposed to X-rays and iron ions having a dose-averaged LET at 200 keV/micrometer in the presence or absence of DMSO, and the cell survival was determined using the colony formation assay. The contributions of indirect action of 76% and 50% were found for X-rays under oxic and hypoxic conditions, respectively. In contrast, the contributions of indirect action for iron ions were estimated to be 42% and 32%. The RBE values were 2.8 for oxic and 5.3 for hypoxic, and the OER values were 2.8 for X-rays and 1.5 for iron ions. When the RBE and OER were estimated separately for direct action (RBED and OERD) and indirect action (RBEI and OERI); the RBED was larger than RBEI under both normal and low oxygen concentrations. The OERD values for both X-rays and iron ions were lower than that for OERI. Thus, direct action of radiation gives a remarkably higher RBE and lower OER for cell killing than indirect action. It is possible that particle beams may be highly effective in treating cancer if the particle therapy can only use the portion of direct action out of total radiation actions; this would be exemplified by the usage of radioactive 9C-ion beams and boron neutron capture., 14th International Congress of Radiation Research (ICRR2011)},
 title = {Direct action is the key to understand the high biological effects caused by particle beams},
 year = {2011}
}