Approach of radiochemistry about cellular lethality in DNA repair-deficient cell lines after heavy-ion irradiation

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We estimated the effects of indirect and direct actions on cell killing using dimethylsulfoxide (DMSO). CHO, xrs6 and 51D1 cell lines under oxic and hypoxic conditions were exposed to several intensities of high-LET radiation (13 to 200 keV/micrometer) in the presence or absence of DMSO and cell survival was determined using a colony formation assay. Under both oxic and hypoxic conditions, the contribution of direct action to cell killing increased with increasing LET. In all cell lines, the RBEs determined at a survival level of 10% increased with LET, and the OERs decreased with LET. When the RBE and OER were estimated separately for direct action (RBE-D and OER-D) and indirect action (RBE-I and OER-I); the RBE-D was larger than RBE-I and the OER-D was smaller than OER-I. Thus the direct action of heavy-ions yielded a remarkably larger RBE and smaller OER for cell killing than the indirect action.