Radiation-induced genomic instability and bystander effects: implications for radiation protection\*

Evidence has emerged over the past decade for the existence of two cellular phenomenons which challenge the standard paradigms for the induction of biological effects by ionizing radiation. In bnth cases, important genetic changes arke in cells that in themselves receive no radiation exposure. In the first, radiation induces a type of transmissible genomic instability in cells that leads to a persistent enhancement in the rate at which genetic alterations including mutations and chromosomal aberrations arise in the descendent5 of the original irradiateà cell aRer many generations of replication. In the bystander effect, damage signals are transmitted from irradiated to non-irradiated ceiis in the population, leading to the Occurrence of biologic effect. in these “bystander” cells. In this review, our current knowledge concerning these two phenomena is described and their potential impact on the estimation of risks of low level radiation exposure discusseà.