INDUCTION OF DNA DSB AND ITS REJOINING IN THE CLAMPED AND NON-CLAMPED TUMORS AFTER CARBON ION BEAMS COMPARED WITH X RAYS

We studied DSB induction and rejoining in the clamped and non-clamped tumors after low- and high-LET radiations. SCCVII cells were transplanted into the right hind legs of C3H male mice. Conditioning irradiation with either 80 keV/μm carbon ions or 200 kVp X rays was delivered to the tumors at 5 mm diameter. Hypoxic cells were produced by clamping tumor-bearing mice 15min before irradiation in situ. Immediately after and 1 hr after irradiation, tumors were excised and rapidly cooled on ice. DSB in the tumors was analyzed by a static-field gel electrophoresis, and assayed for DSB induction and rejoining. The DSB immediately after X rays under normoxic condition was higher than under hypoxic condition. These damages in both tumor conditions were rejoined 60 to 70% within 1 hr in situ. The OER of DSB after X rays was 1.68 ± 0.31, and this value was not changed by 1 hr rejoining incubation (1.40 ± 0.26). On the other hand, no difference between X rays and carbon ions was found for the induction and rejoining of DSB. The rejoined fraction and the OER of DSB after carbon ions were similar to that after X rays. Additionally, the RBE of DSB immediately after and 1 hr after irradiation, these values were 0.9 to 1.3, and were not dependent on gases conditions. The yields of DSB induced by X rays in vivo might be similar to that after carbon ions, because the OER and RBE were not found a major difference.MICROS 2009 15th International Symposium on Microdosimetr