Purpose: To discuss the threshold dose problem in radiation carcinogenesis after a review of the present author's experimental data on mouse tumour induction by chronic beta-irradiation and other relevant data.
Conclusions: A threshold dose-response in radiation carcinogenesis appears in certain tissues and under certain conditions. The optimum condition for demonstrating an apparent threshold is with partial-body chronic or repeated radiation rather than with acute whole-body radiation. Its possible mechanism is host tolerance, involving DNA repair, apoptosis and an immune response activated by low radiation doses. This tolerance level was examined by a survey in the literature of non-tumour-inducing doses, D(nt), the highest dose at which no significant increase of tumours was observed above the control level.