Microdistribution and localized dosimetry of the alpha-emitting radionuclides Pu-239, Am-241 and U-233 in mouse femoral shaft

Purpose: To analyse the temporal change in microdistribution of Pu-239, Am- 241 and U-233 in mouse femur and to compare the calculated radiation doses with regions of the bone marrow thought to contain target cells for osteosa rcoma and leukaemia with relative risk for those diseases. Materials and methods: Neutron-induced and alpha-track autoradiographs were prepared from femora of the CBA/H mouse that had been injected with 40 kBq kg(-1) radionuclide between 1 and 448 days previously. Computer-based imag e analysis of the autoradiographs was performed and dosimetric methods appl ied to obtain radiation dose-rates to different regions of the marrow cavit y. Results: Initially each radionuclide deposited on endosteal and periosteal hone surfaces; Am-241 was additionally deposited on vascular canal surfaces . Redistribution resulted in U-233 being incorporated into bone, while Pu-2 39 and Am-241 showed transfer into both bone volume and marrow. Accumulatio n in the central marrow peaked at 112-224 days post-injection, but subseque ntly was cleared by 448 days. Cumulative doses to both osteosarcomagenic an d myeloid leukaemogenic target cell regions showed the trend Pu-239 > Am-24 1 > U-233. Conclusions: Calculation of cumulative doses to a 10-mu m layer of marrow a djacent to bone surfaces appears to be a suitable predictor for risk of ost eosarcoma. Risks of myeloid leukaemia in the mouse are better predicted by considering the central marrow as the target region rather than average dos e to all marrow.