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.