Treatment of Bone Metastasis with Bone-Targeting Radiopharmaceuticals

Bone is a common metastatic site of cancer. Bone metastasis reduces life expectancy and results in serious symptoms and complications such as bone pain, pathological fractures, and spinal cord compression, decreasing quality of life by restricting sleep and mobility. Treatment for bone metastasis includes drugs (pure analgesics, hormones, cytotoxic chemotherapy, and bisphosphonates, among others), external radiation therapy, surgery, and radionuclide therapy using bone-targeting radiopharmaceuticals. Particulate radiation with α- or β-rays is used as a bone-targeting radiopharmaceutical in radionuclide therapy. β-Emitters have lower energy and a longer range than α-emitters and have less tumoricidal activity and deliver more radiation to adjacent normal tissue. Therefore, the main therapeutic effect of bone-targeting β-emitters such as ⁸⁹Sr-dichloride is bone pain palliation rather than enhanced survival. In contrast, α-emitters such as ²²³Ra-dichloride have high energy and a short range, resulting in greater tumoricidal activity and less radiation damage to adjacent normal tissue. Treatment with bone-targeting α-emitters can improve survival and decrease bone pain. This review focuses on the principles and clinical utility of several clinically available bone-targeting radiopharmaceuticals in metastatic bone disease.