@misc{oai:repo.qst.go.jp:00070946,
 author = {Hirayama, Ryoichi and Matsumoto, Yoshitaka and Koda, Kana and Uzawa, Akiko and Noguchi, Miho and Kase, Yuki and Ito, Atsushi and Matsufuji, Naruhiro and Okayasu, Ryuichi and Furusawa, Yoshiya and 平山 亮一 and 松本 孔貴 and 幸田 華奈 and 鵜澤 玲子 and 伊藤 敦 and 松藤 成弘 and 岡安 隆一 and 古澤 佳也},
 month = {Oct},
 note = {The contribution of indirect action mediated by OH radicals in cell killing can be estimated from the experiment using an OH radical scavenger DMSO, which suppresses indirect action without affecting direct action.  Exponentially growing Chinese hamster ovary cells under oxic and hypoxic conditions were exposed to X-rays and high-LET heavy ion radiations of 15 to 480 keV/micrometer in the presence or absence of DMSO, and their survival fractions were determined using a colony formation assay.  The contribution of indirect action to cell killing decreased with increasing LET under both oxic and hypoxic conditions.  The contributions under hypoxic condition were lower than that under oxic condition at each LET data point.  The RBE and OER were determined at a survival level of 10%.  The RBE values under both oxic and hypoxic conditions increased with LET, reached a peak at around 200 keV/micrometer, and then decreased with LET.  The OER value started to decrease at around 50 keV/micrometer, and became below 2 at around 90 keV/micrometer, and then reached approximately 1 or slightly higher in the very high LET region.  When the RBE and the OER were estimated separately for direct action (RBED and OERD) and indirect action (RBEI and OERI), the RBED under both conditions were larger than RBEI at 90-480 keV/micrometer.  OERD was smaller than OERI at every LET data point.  Thus, the direct action by heavy-ion beams gives a remarkably large RBE and small OER for cell killing in comparison to OH radical-mediated indirect action., 39th Annual Meeting of the European Radiation Research Society},
 title = {High biological effectiveness depends on the direct action by heavy ions},
 year = {2012}
}