量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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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.
会議概要（会議名, 開催地, 会期, 主催者等）
39th Annual Meeting of the European Radiation Research Society
High biological effectiveness depends on the direct action by heavy ions
