Consideration of age-dependent radium retention in people on the basis of the beagle model

This paper examines in humans the proposition emanating from studies in beagles that initial retention of radium varies in proportion to the calcium addition rate at the time of intake. Human calcium addition rates were scaled from those in beagles, the relative calcium accretion rates in the two species at equivalent stages of skeletal growth providing the scaling factor. The variation of radium retention with age was determined by fitting a modified power function to data on the retention of radium from about 30 to 15000 days following a series of therapeutic injections of 226Ra in humans ranging in age from 18 to 63 yr. The fractional retention R at t days following a single injection of 226Ra was described by R = (1 + t/d)-0.44. The age-dependent parameter d in the retention function was found to be proportional to the calcium addition rate at the time of injection in subjects receiving less than 200 micrograms 226Ra.