Radioisotopes are radioactive substances given by mouth as a drink or capsules, or injected into a vein. Cancer cells absorb radioisotopes more than normal cells and so get a higher dose of radiation. This causes the cancer cells to die.
The advantage of radioisotope treatment is that all the bones affected by cancer will be treated. So it can be a helpful treatment if several of your bones are affected.
There are different types of radioisotopes. The type you have will depend on the type of primary cancer you have.