Bystander Effect and Radiation Risk: a theoretical approach

The concept of dose-response linearity has been in practice for risk assessment of chemical carcinogens and ionising radiation for the past 30 years. But in recent years the evidence from cancer mortality studies and new radiobiological phenomena such as genomic instability, the bystander effect and adaptive response have challenged this accepted hypothesis questioning whether low dose linearity is also appropriate for low dose risk assessment. Generally, the linear-no-threshold model (LNT) implies: that cancer is a stochastic process; that the dose response for a particular effect is additive; that the genomic instability is of no relevance to cancer; and that ionising radiation is not a unique carcinogen. These assumptions are generally not supported by experimental data which are mainly carried out at relatively large doses, neither by theoretical considerations.