Possible implications of non-linear radiobiological effects for the estimation of radiation risk at low doses.

Possible implications of the effects of low LET radiation on the induction of cancer at low doses are studied. Low dose hypersensitivity and adaptive response were identified as candidates which may give a non-linear dose effect curve for acute exposures, whereas adaptive response may influence protracted exposures. In this paper acute exposures are studied. Several radiobiological reports on studies with mammalian cell lines have indicated the presence of a hypersensitive region in the radiation survival response at low doses followed by an increase in radioresistance. The two step clonal expansion (TSCE) model for the process of carcinogenesis was adapted in such a way that cell killing after acute radiation induces increased clonal expansion for some time and thus gives a promoting effect of radiation. As a first step, the Radiation Effects Research Foundation (RERF) data on the lung cancer incidence are fitted to study how such a model would influence the assessment of the cancer risk at low doses.