Radioisotope therapy delivers radiation directly into the cancer cells. You are given the radioisotope or radionuclide usually as a capsule, drink or injection into a vein. Cancer cells absorb the radioactive substance more than normal cells. This means they receive a higher dose of radiation, causing the cells to die.

There are different types of radioisotope treatment depending on what type of cancer you have:

  • Iodine-131 is used to treat certain types of thyroid cancer and some rarer types of cancer. You may need to stay in hospital for this treatment.
  • Strontium-89 and samarium-153 is used to treat some types of secondary bone cancer. They can help reduce pain.
  • Radium-223 is a new radioisotope therapy that is used to treat secondary bone cancer.

Radioisotope therapy can make you radioactive for some time afterwards. Your doctor will tell you about any precautions you will need to take when you go home.

What is radioisotope therapy?

This therapy uses radioactive substances known as radioisotopes or radionuclides. Radioisotopes are given by mouth as a drink or capsules, or injected into a vein (intravenous injection). Cancer cells absorb the radioisotope more than normal cells do and receive a higher dose of radioactivity. This eventually destroys the cancer cells.

Before you have any treatment with a radioisotope, you will be given detailed information about it.


This is the most common type of radioisotope treatment. It’s used to treat specific types of thyroid cancer. It’s also used to treat some rarer types of cancer, such as neuroblastoma (a cancer that develops from particular types of nerve cells). It is usually given as capsules or a drink, but can also be given as an injection into a vein in the arm. Some of these treatments involve a stay in hospital.

Radioactive iodine makes you slightly radioactive for a while after your treatment. During this time, the radioactivity will slowly leave your body in your urine, bowel motions (stools), blood (if you have a period), saliva and sweat. You’ll need to follow safety measures after treatment and for a short time after going home.

Your hospital team will give you more detailed information about radioactive iodine treatment and the safety measures needed.

Strontium-89 and Samarium-153

These radioisotopes can be used to treat certain types of secondary bone cancer. This is when cancer has spread to the bones from somewhere else in the body. The radioisotopes help to reduce bone pain and improve quality of life. You can usually go home soon after having this treatment.


You may have radium-223 to treat secondary cancer in the bone from prostate cancer that is no longer responding to hormonal therapy. You can usually go home soon after having this treatment.

Radium-223 is not available in all parts of the UK. Your specialist can give you more information about whether it is available to you.

Back to Internal radiotherapy explained


Brachytherapy treats cancer by placing a high dose of radiation directly inside or near to the tumour.