Medical oncologist Michael Morris of Memorial Sloan-Kettering’s Genitourinary Oncology Service describes new injectable radiopharmaceutical agents used to treat bone metastases from castration-resistant prostate cancer. These alpha-emitting agents deliver high, lethal doses of radioactive energy over a small distance. Because the energy they emit penetrates only through the depth of a small number of cells the process leads to fewer side effects than the (primarily palliative) older beta-emitting radiopharmaceutical agents. Memorial Sloan-Kettering was the first center to bring one of these alpha emitters, radium-223, to the United States. It was also the first institution to combine the use of the radiopharmaceutical with chemotherapy. The FDA approved the agent for commercial use in May 2013.