Competitive Radiation-induced Carcinogenesis: an Analysis of Data From Beagle Dogs Exposed to 226Ra and 90Sr

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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 eight intravenous injections of 226RaCl2 (one injection every 2 weeks for 4 months) starting at 14 months of age. Analysis of incidence of each disease in 776 beagles showed a normal probability density function with respect to time. Median incidence time and standard deviation 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 radium, for beagles injected (A°) with 83.6 microCi 226Ra, to 11.5 yr of age for beagles given A° = 3.14 microCi 226Ra. 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 micro Ci 90Sr/day to 12.6 yr at 4 microCi 90Sr/day. Tumor yield was calculated assuming that the causes of death from competing diseases were mutually 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 226Sr by injection and inhalation. Extrapolation of the observed dose effects to lower levels of administered radioactivity (comparable to maximum permissible body burden) is discussed within the frame of a competitive mortality.

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