Skeletal uptake and lifetime retention of 90Sr and 226Ra in beagles

Skeletal uptake and retention of graded doses of ingested or injected 90Sr and injected 226Ra have been studied in 863 beagles; measurements of skeletal burden were made up to a maximum lifetime of 18.5 years. Doses ranged from 0 in 162 controls to levels that markedly reduced life span. Skeletal uptake of the administered doses averaged 2 to 2.3% for 90Sr fed to 388 beagles from midgestation to age 540 days, 33 to 35% for 45 dogs that were given single intravenous injections of 90Sr at age 540 days, and 37 to 45% for 226Ra given in eight fortnightly intravenous injections to 253 dogs from age 435 to 540 days. Skeletal retention was evaluated from the time when uptake ended until death, which occurred, on the average, at 14 to 14.5 years for the lower levels. Simple two-parameter power functions of the form SB(t) = at-b, with SB the skeletal burden, t the time after beginning of intake, and a and b fitted parameters, but corrected for radioactive decay, were used to describe the whole-skeleton retention of deposited 90Sr or 226Ra, as well as in 17 skeletal subgroups. The negative logarithmic slope, b, of these power functions for whole skeleton was about the same for both 90Sr and 226Ra, with an average value of 0.30 +/- 0.05 SD, indicating a common clearance mechanism. The lifetime average cumulative absorbed dose to irradiated skeleton varied from 0.38 to 107 Gy for beta rays in the 90Sr studies and from 0.94 to 167 Gy for alpha particles in the 226Ra studies. Daily dose rates to the skeleton for singly injected 90Sr fell rapidly after injection and declined to about 10% of the peak values late in life. Rates declined more slowly to 40-50% of peak values in other treatment groups. The time-weighted average dose rate for fed 90Sr and injected 226Ra was a robust measure that declined only about 20% late in life compared to peak values. The lifetime average dose rate varied from 0.08 to 133 mGy day-1 for the 90Sr studies and from 0.21 to 162 mGy day-1 for the 226Ra studies. Lifetime doses to mandible and cervical vertebrae for the intermediate dose levels of fed 90Sr were calculated to be about 40% higher than the skeletal average.