Dose and dose-rate dependence of mutation frequency under long-term exposure - A new look at DDREF from WAM model -

We investigate the dose and dose-rate dependence of the mutation frequency caused by artificial radiations with Whack-A-Mole (WAM) model which we have recently proposed. In particular, we pay special attention to the case of long-term and low dose-rate exposure. The results indicate that the dose-rate dependence is successfully described with WAM model and it may replace the so-called DDREF, the concept of which has long been adopted to take account of the difference between the high dose-rate data and the low dose-rate ones. Basic properties of WAM model are discussed emphasizing the dose-rate dependence to demonstrate how the explicit dose-rate dependence built in the model plays a key role. By adopting the parameters that are determined to fit the mega mouse experiments, biological effects of long-term exposure to extremely low dose-rate radiation are discussed. In WAM model, the effects of the long-term exposure show a saturation property, which makes a clear distinction from the LNT hypothesis which predicts a linear increase of the effects with time.