Osteosarcoma Risk after Simultaneous Incorporation of the Long-Lived Radionuclide ^{227}{\rm Ac}$ and the Short-Lived Radionuclide ^{227}{\rm Th}

The effect of injection of 1.85 kBq/kg of the long-lived radionuclide ^{227}{\rm Ac}$ 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 ^{227}{\rm Th}$ was investigated. The highest absolute osteosarcoma incidence was observed with the highest doses of ^{227}{\rm Th}$. Addition of ^{227}{\rm Ac}$ resulted in an additional osteosarcoma incidence only at the lowest dose of ^{227}{\rm Th}$ and did not affect the osteosarcoma incidence resulting from higher doses of ^{227}{\rm Th}$. The longest times to tumor appearance were observed with ^{227}{\rm Ac}$ 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 ^{227}{\rm Th}$ and ^{227}{\rm Ac}$ but different after injection of each radionuclide alone.