EUROPEAN RADIATION RESEARCH 2012

Large RBE and small OER in heavy-ion induced biological effects mainly depend on direct action

18 Oct 2012, 16:26

1m

Poster Hall (Vietri sul Mare)

poster preferred Charged Particles in Medicine and Space Research Poster Session 3

Speaker

Dr Ryoichi Hirayama (NIRS/National Institute of Radiological Sciences)

Description

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 (RBE-D and OER-D) and indirect action (RBE-I and OER-I), the RBE-D under both conditions were larger than RBE-I at 90-480 keV/micrometer. OER-D was smaller than OER-I 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.