Radium-224 Retention, Distribution, and Dosimetry in Beagles

The retention, distribution, and dosimetry of injected^{224}{\rm Ra}$were studied in six young adult beagles killed 0.04 to 7 days after^{224}{\rm Ra}$administration. Biological retention of^{224}{\rm Ra}$in the skeleton averaged 48% (37 to 60%), and soft-tissue retention decreased from 61% at 0.04 days to 6% at 7 days. At death there was more^{212}{\rm Pb}$in red blood cells and liver than the amount in transient equilibrium with the^{224}{\rm Ra}$in these tissues. There was an excess of212Bi over^{224}{\rm Ra}$in kidneys, and a deficiency of both^{212}{\rm Pb}$and212Bi relative to^{224}{\rm Ra}$in eyes and bone. The retention equations derived from the data suggest that the fractional escape of220Rn produced in bone by^{224}{\rm Ra}$decay was roughly 0.08. From the retention of^{224}{\rm Ra}$,^{212}{\rm Pb}$, and212Bi in the skeleton and selected soft tissues, it was calculated that the injection of 1 μCi^{224}{\rm Ra}/{\rm kg}$into an adult beagle having 75 g skeleton/kg body results in cumulative average doses to the blood-filled organs of 40 rad to the skeleton, 13 rad to the kidneys, 8 rad to the liver, 11 rad to the eyes, and 0.8 rad to the testes and ovaries.