Abstract
In this experiment cells were irradiated continuously with low-dose-rate (LDR) radiation (0.3 mGy/min) in a confluent state up to 2 weeks. Cellular survival after LDR was much increased compared with the same dose of high-dose-rate (HDR) radiation (2 Gy/min). In accordance with the survival result, induction of micronuclei was also much reduced after LDR irradiation. Induction of mutation of the HPRT gene was also much lower after LDR than HDR. When activation of the ATM and p53 proteins were analyzed, significant amount of phosphorylation of ATM and p53-Ser15 was observed after HDR but little phosphorylation was observed after LDR We then analyzed focus formation of phosphorylated histone H2AX protein after irradiation. After HDR, dose dependent increase in number of foci was observed but after LDR almost no increase was observed, even at the highest dose. These results suggest that in normal cells DNA damage induced by LDR, which is very scattered in time and space, was effectively repaired and effect of LDR on normal human cells is also much smaller than that of HDR.
