Comparison of the carcinogenicity of radium and bone-seeking actinides.

The relative effectiveness of nine bone-seeking radionuclides with their progeny for the production of malignant skeletal tumors (mostly osteogenic sarcoma), principally by chronic alpha-particle irradiation, is examined with available data obtained from lifetime studies at three laboratories of pure-bred beagles exposed to graded dosages in controlled experiments. The lifetime tumor dose-rate/time-response relationships observed in beagles injected with 226Ra at the University of California at Davis, in which 123 cases of bone cancer (98% osteosarcoma) have been observed for dose rates between 0.05 and 20 rad/day, provide the basis for comparing the induction of bone cancer by the other radionuclides. All nine radionuclide studies were found to demonstrate with high precision (sigma g less than 1.2) a three-dimensional lognormal response relationship represented in two dimensions by the equation of the time to death from bone cancer t = KD-s, where t is the elapsed time to death, D is the average skeletal dose rate, K is a parameter characteristic of the radionuclide, risk level and exposure details, and S observed to be 0.29 (0.01 SE) and suggested to be exactly one-third for all the nine radionuclides. The results show the relative biological effectiveness (RBE) for bone-cancer induction potency with respect to radiation exposure from 226Ra to be 3.0 for 228Ra , 6.4 for 241Am, 6.6 for 249Cf , 252Cf and 253Es , 9.0 for 239Pu, 10.7 for 228Th , and 15.5 for 238Pu. The observed RBE values are interpreted in terms of the relative exposure of sensitive cells of the skeleton since they all involve primarily alpha irradiation. Scaling to people is accomplished using a response ratio (RR) of 3.6 with respect to beagles.