Keywords: radiation, cancer, threshold dose, dose rate, review of cancer data, cancer risk, ionising radiation, low dose irradiation, tumor data
Threshold dose problems in radiation carcinogenesis: a review of non-tumour doses
Non-tumour-inducing doses exist in dose-response data on experimental animals and humans, although a linear non-threshold model has been adopted for estimating cancer risk of ionising radiation at a low dose region for radiation protection purposes. Here, data on non- tumour dose, Dnt, the maximum dose at which a statistically significant increase of tumours is not observed, were reviewed in the literature. Dnt values range from 0.1 to 3 Gy for a variety of tumours induced by acute whole-body irradiation at low LET. This becomes one order higher by fractionation of radiation dose and further by extending irradiation chronically. Non-tumour doses for irradiation of a part of the body are one order higher than those for whole-body irradiation, indicating a higher tolerance level in the partial-body irradiation. Tumour data with high LET radiation also show non-tumour dose and its decrease at a very low dose rate. The variation of Dnt is explained by the host tolerance, including inducible and non-inducible DNA repair, apoptotic elimination of unrepaired cells, and immunological suppression of tumour development.