Retention of Radium in Man

Abstract

While a recent injection of ${}^{223}{\rm Ra}$ was retained as $t^{-0.50}$ , a long-term burden of226 Ra in the same man decreased as $t^{-1.7}$ . This dramatic difference in the rate of change of retention is predicted by the modified power function model with an observed rate of excretory plasma clearance of 126 liters/day. From the ${}^{223}{\rm Ra}$ data, the model predicts that the226 Ra burden should have reached transient equilibrium within the body ( $t_{{\rm y}}=6.7$ years) so that its retention today can be described by a final exponential. With a somewhat lower average rate of plasma clearance (72 liters/day, $t_{{\rm y}}=20$ years) the model would be consistent with the retention functions of Norris et al., Miller and Finkel, and the halftime for retention reported by Keane and Evans. Accordingly, it would be most interesting to measure the rates of plasma clearance in the...