Interspecies Scaling of Risk for Radiation-induced Bone Cancer

Summary

The induction of bone cancer in mice, dogs and humans, due to protracted α-irradiation from skeletal burdens of radium, was found to be represented by a single dose-rate/time/response function, when time was normalized with respect to species natural life-span. In the absence of other causes of death, the median time to death from bone cancer after ²²⁶Ra intake is given by t*_m = 790d¯^{* ? 0·29}, based on the dog data, with d¯* the time-weighted average absorbed dose rate in cGy/mLSF to skeleton and where time is measured as milli-life-span-fraction. On the basis of life-span scaling of the time dimension, data on cancer induction from studies with laboratory animals can be scaled to estimate human risks in a three-step process involving a three-dimensional analysis. The overall cancer risk distribution is shown to be a mountain-like surface rising from a Euclidean plane formed by the dose rate and survival time co-ordinates. At lower dose rates the time required for cancer induction may exceed the natural life-span yielding a quasi-threshold for cancer risk. For intakes of ²²⁶Ra in young adults this quasi-threshold is predicted to occur at a cumulative life-time α-radiation dose to the skeleton of about 1 Gy.