Sm153

Samarium-153 (Sm-153) is a radioisotope of the element samarium. It has a mass number of 153 and a half-life of about 46.3 hours. Sm-153 decays by beta emission to europium-153 and also emits low-energy gamma photons, notably around 103 keV, which allows its distribution to be monitored by imaging techniques.

Sm-153 is produced in nuclear reactors through neutron irradiation of samarium, typically natural samarium or enriched Sm-152. After irradiation, Sm-153 is chemically separated from the target material and formulated for use as a radiopharmaceutical. The isotope’s relatively short half-life makes it suitable for clinical applications where rapid localization and prompt dose delivery are advantageous.

In medicine, Sm-153 is best known for its role in bone pain palliation in patients with metastatic cancers, such as breast or prostate cancer. When bound to a bone-seeking ligand, most commonly ethylenediamine tetramethylene phosphonate (EDTMP), the resulting compound Sm-153-EDTMP concentrates in areas of increased bone turnover, such as osteoblastic lesions. The radiopharmaceutical is given intravenously; it delivers targeted beta radiation to painful bone metastases while emitting gamma rays that enable imaging and dose verification. Aimed primarily at reducing pain rather than curing disease, its effectiveness varies among patients.

Safety considerations include potential bone marrow suppression, reflected in temporary declines in blood cell counts. Because of its radioactivity and renal clearance, Sm-153 therapy is administered under specialized nuclear medicine protocols with appropriate patient selection and monitoring. Regulatory status and availability vary by country, reflecting the balanced benefits and risks of palliative radiopharmaceuticals.