Abstract
Estimation of the scientific risks of high dose radiation has been successfully quantified by many studies using several different approaches. However, the risk for low and low dose-rate radiation is obscure because of a lack of evidence. This risk is currently estimated by extrapolating the radiation response at high doses into low dose ranges for practical purposes. Recent challenges to examine directly the biological responses to low dose radiation using newly developed technologies are unveiling interesting alterations at the molecular level. The interpretation of these data, however, needs careful consideration because they may not be related to any change in biological functions.