DNA DSB induction and rejoining in V79 cells irradiated with light ions: a constant field gel electrophoresis study.

PURPOSE To study the induction and the time-course of rejoining of DNA double strand breaks (DSB) in V79 cells irradiated with light ions with different linear energy transfer (LET). MATERIALS AND METHODS V79 cells were irradiated in monolayer with monoenergetic proton, deuteron, helium-3 or helium-4 ion beams, each at two different energy values. Gamma rays were used as reference radiation. DSB have been measured by constant field gel electrophoresis (CFGE). RESULTS The initial yield depended little on the particle type and LET. The amount of DSB left unrejoined for up to 2 h incubation time could be roughly described by a decreasing exponential function with a final plateau, although more complex functions cannot be excluded. Radiation quality had little effect on the rejoining rate but affected the plateau. The amount of residual DSB after 2 h was higher for densely than for sparsely ionizing radiation, and for the same particle was dependent on LET. The corresponding RBE ranged from 1.8 to 6.0. CONCLUSIONS The results support the hypothesis that complex, less reparable DSB are induced in higher proportion by light ions with respect to gamma-rays and that, for the same ion, increasing LET leads to an increase in this proportion.