Osteosarcoma risk after simultaneous incorporation of the long-lived radionuclide 227Ac and the short-lived radionuclide 227Th. 
The effect of injection of 1.85 kBq/kg of the long-lived radionuclide 227Ac on the induction of osteosarcomas in female NMRI mice by different dose levels (18.5, 74, and 185 kBq/kg) of the short-lived radionuclide 227Th was investigated.  The highest absolute osteosarcoma incidence was observed with the highest doses of 227Th.  Addition of 227Ac resulted in an additional osteosarcoma incidence only at the lowest dose of 227Th and did not affect the osteosarcoma incidence resulting from higher doses of 227Th.  The longest times to tumor appearance were observed with 227Ac alone.  The latent period in two different age groups (4 weeks and 10-12 weeks) appeared to be similar following injection with combined doses of 227Th and 227Ac but different after injection of each radionuclide alone.