Estimation of DNA double-strand breaks induced by laser-driven proton beams

レーザー駆動陽子線の照射によるDNA2本鎖切断の評価

余語 覚文

Yogo, Akifumi

Laser-acceleration of ions has been suggested as an alternative approach to conventional accelerators for ion beam radiotherapy (IBRT). To investigate the effects of high dose rate that is attributed to high ion current, short bunch irradiation we have developed an experimental setup that uses laser-accelerated protons. In-vitro human lung cancer cells: A549 pulmonary adenocarcinoma are irradiated with a laser-accelerated proton bunches of duration, s and flux, cms, amounting to single bunch absorbed dose at the 1 Gy level. The double-strand break (DSB) yield in cell DNA is analyzed using the phosphorylated histone H2AX (-H2AX) immunostaining method. By counting the number of -H2AX foci apparent on the microscopic images, we estimate the DSB yield to be 41 DSBs/nucleus/Gy for single bunch irradiation of laser-accelerated protons. We determine the relative biological effectiveness (RBE) for DSB induction to be 1.470.38 for a laser-accelerated proton beam at an average LET of 41 keV/m. This RBE value is comparable to those for light ions delivered by conventional accelerators. Irradiation by laser-accelerated protons has been shown to be effective for DSB induction in cancer cell DNA. However, we observe no DNA DSB effects that can be attributed to the high-current irradiation when the beam flux is increased up to cms used in the present experiment.