Xofigo aims to attach itself to bone metastases, treating the bone metastases through radiotherapy from within. When bones grow, they store calcium. Xofigo is very similar to calcium in structure and so the body absorbs it into the bones like calcium. When prostate cancer spreads to the bones, these areas have a higher calcium uptake than healthy bones, and can store especially high amounts of Xofigo. Xofigo has a radioactive part (radium-223) that releases short bursts of radiation (alpha radiation) into the nearby area. The bone metastases are therefore destroyed from within, while the surrounding healthy tissue is protected as