A biokinetic model for alpha-emitting bone surface-seeking radionuclides in the mouse skeleton

Following intake of an alpha-emitting bone surface-seeking radionuclide, such as Pu-239 or Am-241, a major site of retention is the skeleton. Within the skeleton, these radionuclides are initially deposited on the bone surfaces, but subsequently redistributed as a result of the process of bone remodelling. In this study, these processes have been modelled in the mouse femoral shaft, by development of a multicompartmental biokinetic model. The model consists of bone surface, volume and marrow and blood compartments, each of which are described by input parameters. The majority of parameter values were obtained from current literature, and the remainder obtained by fitting of the model to microdistribution and radiation dosimetry data taken from previous autoradiographical analyses of the mouse femoral shaft, at times from 1 to 448 days after a 40 kBq.kg(-1) injection of either Pu-239 or Am-241. Results of fitting the model to these data predict that (a) Pu-239 and Am-241 show equal affinities for both resorbing and forming bone surfaces, (b) Am-241 is retained in macrophages for a longer period than Pu-239 and, (c) the cumulative dose to the region of marrow containing the osteosarcomagenic target cells is higher for Pu-239 than Am-241 by a factor of two.