Competitive Radiation-induced Carcinogenesis

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Abstract
The incidence of radiation-induced primary bone sarcoma and myeloproliferative diseases was studied as a function of dose rate and time in beagles that were fed diets containing 90SrCl2 in equilibrium with 90Y from midgestation to 1.5 yr of age or that were administered 8 i.v. injections of 226RaCl2 (1 injection every 2 wk for 4 mo.)starting at 14 mo. of age. Analysis of incidence of each disease in 776 beagles showed a normal probability density function regarding time. Median incidence time and SD from the mean of distribution were calculated for primary osteosarcoma at each level of administered radioactivity. The median incidence age (T) for mortality from primary osteosarcoma increased from 4.1 yr of age, 2.6 yr after final injection of Ra, for beagles injected (Ao) with 83.6.mu.Ci226Ra, to 11.5 yr of age for beagles given Ao = 3.14.mu.Ci226Ra. A similar increase in T was observed for beagles that ingested a daily diet containing 90Sr + 90Y, from T = 2.8 yr of age at 36.mu.Ci90Sr/day to 12.6 yr at 4.mu.Ci90Sr/day. Tumor yield was calculated assuming that the causes of death from competing diseases were mutally exclusive with respect to individual diseases. Incidence and cumulative incidence for each of the diseases were calculated as a function of time and maximum dose rate. These analyses were extended to beagles administered 226Ra by a single injection or 90Sr by injection and inhalation. Extrapolation of the observed dose effects to lower levels of administered radioactivity (comparable to maximum permissible body burden) was discussed within the frame of a competitive mortality.