Dose-rate effects on the induction of DNA double-strand breaks with heavy-ion irradiation

The deproteinized DNA samples of melanoma cells (B16) were irradiated by 50 MeV/u 1212C6+ of different dose rates. And the inverse pulsed-field gel electrophoresis were employed to measure the distribution of DSB fragments. The results show that both of the percentages of DNA released from plug (PR) induced by 3 Gy/min and 30 Gy/min increase with the rising dose and approach a similar quasi-threshold. The yields of DSB induced with 3 Gy/min are 0.40DSBs/(100 Mbp. Gy) while those induced with 30 Gy/min are not obtained. The cross section of DSB induction with 30 Gy/min is 2.14 m2, which is more than three times of that with 3 Gy/min. These show that the higher the dose rate is, the more efficiently DSBs are induced. There is a peak about 860 kbp of DSB fragments induced with 3 Gy/min, which does not exist in the samples treated with 30 Gy/min. It is implied that the dose rate has influence on the distribution of DSB fragments