Non-DNA-Targeted Effects and Low-Dose Radiation Risk

Non-DNA-targeted effects of ionising radiation are defined as effects triggered by radiative energy deposition in cellular targets other than nuclear DNA; these include radiation-induced bystander effects and processes that can be mediated via bystander mechanisms, Such as genomic instability and adaptive responses. Laboratory studies show that these responses are favoured by heterogeneous irradiation conditions. Heterogeneous conditions occur at low doses and low dose rates where radiation tracks are sparsely distributed over a cell population; this situation favours bystander signalling between hit and non-hit cells. Non-DNA-targeted effects are currently considered to be candidate mechanisms for any failure of the linear no-threshold (LNT) model to extrapolate radiation risk estimates accurately down to low doses. Some non-DNA-targeted effects have the potential to increase low-dose risk above the LNT extrapolation, and others could decrease the risk.