Life span dynamics of intra-skeletal radionuclide distribution in radium-injected beagles

The distribution of 226Ra activity among the bone groups of the skeleton has been measured as a function of time after exposure for 12 beagles. The dogs were given 8 semi-monthly injections of radium totalling 0.37 microCi/kg, 1.11 microCi/kg, or 3.33 microCi/kg between the ages of 435 and 535 days. They were then sacrificed from 27 to 2764 days after the last injection. The fractional contribution of individual bone groups to the initial skeletal radioactivity distribution changed during the time of this study; the maximum decrease was a factor of 0.54 and the maximum increase was a factor of 1.58. Using a partitioned clearance model, the whole-body retention function characteristic of beagles exposed to radium levels less than or equal to 3.33 microCi/kg was partitioned into two functions representative of cancellous and compact bone. The functions were incorporated into a mathematical description of the 226Ra distribution data in a manner that provides estimates for the fraction of cancellous and compact bone in each skeletal component. Comparison of dosimetric estimates and site-specific tumor occurrence for these beagles revealed an apparent 90-fold variation of dose-response among the bone groups studied.