Marrow-Sparing Effects of 117mSn(41)Diethylenetriaminepentaacetic Acid for Radionuclide Therapy of Bone Cancer

have been used to treat bone pain. The limiting factor in this modality is marrow toxicity. Our hypothesis is that marrow toxicity can be reduced while maintaining therapeutic efficacy using radionuclides that emit short-range b particles or conversion electrons (CEs). A recent study on 47 patients using the short-range CE emitter 117mSn(41)diethylenetriaminepentaacetic acid (117mSn(41)DTPA) supports this hypothesis. The hypothesis is now tested using 117mSn(41)DTPA in a mouse femur model. Methods: The survival of granulocyte–macrophage colony-forming cells (GM-CFCs) in femoral marrow is used as a biologic dosimeter for bone marrow. The dosimeter is calibrated by irradiating mice with exponentially decreasing dose rates of 137Cs g-rays with a dose-rate decrease half-time, Td, equal to the effective clearance half-time of 117mSn(41)DTPA from the femur (222 h). When Td 5 222 h, the mean absorbed dose required t