Incidence of Radiation-induced Skin Tumours in Mice and Variations with Dose Rate

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Abstract
Mice were exposed to weakly penetrating beta-particles from an external source, using 12 different surface doses ranging from 5·4 to 260 Gy and given at four different dose rates from 200 to 1·7 cGy/min. As in previous investigations, both epidermal and dermal tumours occurred with the latter predominating. The lowest surface dose to produce a statistically significant increase in skin tumours was 21·7 Gy, no effect being detected with doses of 5·4–16·3 Gy. The dose–response curves rose steeply when obvious increases occurred. Consideration of these findings and the fact that radiation-induced skin tumours can have an exceptionally long latent period leads to the suggestion that there is some relatively radioresistant factor which normally restrains potential radiation-induced cancer cells in the skin from becoming tumours until the skin is subjected to high local doses. Tumour-induction was unaffected by reducing the highest dose rate by a factor of 10 and the dose–response curves were almost identical. Further reductions of dose rate, encompassing a further factor of 10, in general resulted in fewer tumours.