Induction of DNA DSB and its rejoining in clamped and non-clamped tumours after exposure to carbon ion beams in comparison to X-rays

Hirayama, Ryoichi*; Uzawa, Akiko*; Matsumoto, Yoshitaka*; Noguchi, Miho; Kase, Yuki*; Takase, Nobuhiro*; Ito, Atsushi*; Koike, Sachiko*; Ando, Koichi*; Okayasu, Ryuichi*; Furusawa, Yoshiya*

We studied double-strand breaks (DSB) induction and rejoining in clamped and non-clamped transplanted tumours in mice leg after exposure to 80 keV/m carbon ions and X-rays. The yields of DSB in the tumours were analysed by a static-field gel electrophoresis. The OER of DSB after X-rays was 1.68, and this value was not changed after 1 h rejoining time (1.40). These damages in oxygenated conditions were rejoined 60-70% within 1 h in situ. No difference was found between the exposure to X-rays and carbon ions for the induction and rejoining of DSB. Thus, the values of OER and rejoined fraction after exposure to carbon ions were similar to those after X-rays, and the calculated relative biological effectivenesses of carbon ion were around 1 under both oxygen conditions. The yields of DSB in vivo depend on exposure doses, oxygen conditions and rejoining time, but not on the types of radiation quality.