When the bone is damaged, the body naturally begins to repair the affected area. Calcium is a key nutrient in bone redevelopment, and as the bone begins to repair, the affected area absorbs the vast majority of calcium in the blood.

Secondary bone metastases, much like a healing bone, will absorb a large amount of calcium as the cancerous cells divide uncontrollably.

Radionuclide therapy uses the fact that secondary bone metastases absorb vast amounts of calcium to its advantage. A radioactive substance (radioisotope) is injected that, when in the body, behaves much like calcium.

This radioisotope will be absorbed by areas of bone where there is a high metabolic rate, i.e. where cells are rapidly dividing. In the case where secondary bone metastases have developed, the cancerous cells absorb the radioisotope.

They will then deliver a highly localised radiation dose directly to the affected area while avoiding other areas of healthy bone. Due to the nature of the absorption, the radioisotope is able to treat multiple sites of secondary bone metastases simultaneously.

The radiation damages the secondary bone metastases and provides relief from pain. The period of pain relief can be varied depending on the radioisotope used. The two radioisotopes commonly used are strontium and samarium.

Both radioisotopes may be used where the primary cancer is either prostate or breast.

While strontium provides long-term pain relief, it can take several weeks for the patient to respond. Samarium meanwhile has a quick response but will not provide the longevity that strontium does.