Host: The Japan Radiation Research Society, Chairman of the 52nd Annual Meeting, Toshiteru Okubo (Radiation Effects Research Foundation)
The biological effects of ionizing radiation are characterized by dose-rate effects (DREs). However the mechanisms of DREs have not been clarified. We hypothesize that the DREs might be induced quantitatively by the time-dependent accumulation of unrepaired DNA damages. It is necessary to examine the time course of radiation-induced DNA damage in detail to prove our hypothesis. First, we investigated the time course analysis of radiation –induced DNA damage based on phosphorylated ATM forms discrete foci in primary human fibroblasts. The result showed that the number of unrepaired DNA damages is 0.66 per cell at 30 min after 20 mGy. Next, we examined whether unrepaired DNA damages is accumulated by repetitive 20 mGy irradiation every 30 min. The number of unrepaired DNA damages was 0.65~0.7 per cell by 1~4 repetitive irradiation. This result indicated that unrepaired DNA damage is not accumulated by repetitive irradiation. Thus, we found that the mechanism of DREs is not able to explain from a model of DNA damage and repair.
