The dose-response relationships for tumor induction after high-LET radiation.

This paper presents a review of several studies conducted in our laboratory to examine the carcinogenic effects in mice of high-LET radiation and, for comparison, of low-LET reference radiation. For some specific end-points the following conclusions can be formulated: i) the dose-response curves for myeloid leukemia and malignant lymphoma can be interpreted in terms of induction and inactivation; in particular, the data confirmed that a linear dependence of the induction on dose is adequate to describe the response to fission neutrons, while a pure quadratic dependence is consistent with the experimental data for low-LET radiation; ii) in the liver, a marked age-dependence was demonstrated for radiation-induced tumors with a much higher susceptibility in young than in old mice; also for these tumors the dose-effect curves can be described by a linear and a quadratic relationships for high and low-LET radiation, respectively; iii) data on ovarian tumor induction suggested threshold-like dose responses: these peculiar shapes as well as the absence of a clear radiation quality dependence of the curves are difficult findings to explain using a simple model of radiation action, and they might better be related to a non-stochastic effect of hormonal imbalance following irradiation.