A type of radiation therapy in which a radionuclide (a radioactive chemical) is linked to a cell-targeting molecule, such as a monoclonal antibody, and injected into the body. The cell-targeting molecule binds to a specific target found on some cancer cells. This may help kill the targeted cancer cells while limiting the harm to normal cells. Molecular radiation therapy is used to treat prostate cancer and some other types of cancer. Also called targeted radionuclide therapy.