Extranuclear target and low dose radiation risk assessment

The classical dogma of radiation biology stated that the genotoxic effects of ionizing radiation such as mutations and carcinogenesis are due mainly to direct damage to the nucleus. Recent evidence accumulated from both in vitro and in vivo studies, however, suggested that extranuclear target and the bystander effects may play an important role in mediating the radiobiological effects of both high and low LET radiations. These data indicate that the relevant target for various radiobiological endpoints is larger than an individual cell and suggest a need to reconsider the validity of the linear extrapolation model in making risk estimate for low dose radiation exposure, an issue that is the subject of considerable debate.