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 them 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 the normal cells do and receive a higher dose of radioactivity. This causes the cancer cells to die.

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 and is usually given as capsules or a drink but can also be given as an injection into a vein in the arm. It’s also used to treat some rarer types of cancer, such as lymphoma and neuroblastoma. Some of these treatments involve a stay in hospital.

Radioactive iodine treatment makes you slightly radioactive for about 4–5 days. During this time, the radioactivity will gradually 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 treatment with radioactive iodine and the safety measures that are needed.

We have more information about cancer of the thyroid.

Strontium-89 and samarium-153

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

Strontium and samarium are both given as a single injection through a small tube (cannula) inserted into a vein. After the injection of radioisotope, your urine, bowel motions and blood will be very slightly radioactive for a short time depending on the radioisotope used and the dose given.

You may have to take precautions to reduce any risk to others when you go home. The hospital staff will give you information about this.


This is a new radioisotope treatment for secondary cancer in the bones. It’s still being researched to see how effective it is. It’s mainly been used to treat cancer that has spread to the bones from the prostate, but trials are also looking at its effect on breast cancer that has spread to the bones.

We have more information about strontium-89, samarium-153 and radium-223.

We also have more information on cancer research trials.

Back to Internal radiotherapy explained


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