223Ra

Radium-223 (223Ra) is a radioactive isotope used in oncology as a targeted alpha therapy. It is supplied as radium-223 dichloride. The isotope is bone-seeking and acts as a calcium mimic with a half-life of 11.4 days, decaying via alpha emission through a short decay chain to stable 207Pb. The emitted alpha particles have high linear energy transfer and a short range, causing localized tumor cell kill with limited damage to surrounding tissue.

Indication and regimen: 223Ra is indicated for symptomatic bone metastases in metastatic castration-resistant prostate cancer with no known visceral metastases. It is administered intravenously at 55 kBq/kg every 4 weeks for 4 injections (the Xofigo regimen). It is not curative but can extend survival and delay skeletal-related events. Treatment is generally considered for patients with adequate hematologic reserve and without visceral metastases.

Mechanism and safety: alpha radiation from 223Ra induces double-strand DNA breaks in nearby tumor cells, concentrating dose where osteoblastic activity is high. Safety considerations include hematologic toxicity (anemia and thrombocytopenia), nausea, diarrhea, and fatigue. Hematologic suppression is a major concern, and contraindications include pregnancy. Radiation safety precautions apply to patients and caregivers.

Production and regulatory status: 223Ra is produced for clinical use, typically via actinium-227-based generators, and availability is limited to specialized centers in several countries. Regulatory status includes FDA approval in 2013 for Xofigo, with additional approvals in other regions; ongoing research investigates combinations with other therapies such as androgen deprivation and chemotherapy.