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Radioactive iodine therapy

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This page tells you about radioactive iodine therapy as a treatment for some types of cancer. There is information about


What radioactive iodine is

Radioactive iodine is a type of iodine that is radioactive – iodine 131. It is also called radio iodine. You have radioactive iodine as a capsule or drink. It has no smell and is colourless.


Radioactive iodine for thyroid cancer

Radioactive iodine is a very effective type of treatment for cancer of the thyroid gland. Thyroid cells absorb iodine.

Thyroid gland

The radioactive iodine from the drink or capsule is absorbed into your body and picked up by the thyroid cancer cells wherever they are. So it can kill the cancer cells even if they have spread.

This is known as targeted radiotherapy because the treatment goes straight to the cancer and has very little effect on healthy cells in the body.

You might be asked to eat a low iodine diet before you have treatment with radioactive iodine. Your doctor or specialist nurse might also ask you to change your thyroid hormone medicines or other medicines for a while.


MIBG treatment

Radioactive iodine can be attached to a chemical called MIBG – meta-iodo-benzyl-guanidine. MIBG is taken up by some types of cancer, including 

  • A rare childhood tumour called neuroblastoma
  • A cancer called phaeochromocytoma that affects the adrenal glands
  • Carcinoid tumours

Radioactive iodine attached to MIBG can be used in scans to diagnose these tumours. It is also used to treat these tumour types.


Radioactivity safety procedures

Radioactive iodine treatment can make you radioactive for 4 or more days. The staff tell you about the radiation safety procedures you need to follow. Any radioactive iodine that is not absorbed by your thyroid leaves your body in your sweat and urine.

You need to drink plenty of fluids during your treatment. This helps to flush the iodine out of your body.

You'll be checked regularly for the amount of radiation in your body. You can go home as soon as it falls to a safe level for the people around you, usually after about 4 to 7 days. 

You might be given some safety steps to follow for a while when you get home, for instance if you are in contact with children or pregnant women. Your radiotherapy doctor (clinical oncologist), physicist or specialist nurse explain these to you before you leave hospital.


Side effects of radioactive iodine

Most people don't notice side effects from radioactive iodine treatment. Some people might have a feeling of tightness in the throat. Some people feel flushed but this usually only lasts for about 24 hours. If these effects continue, let your treatment team know. Medicines to reduce inflammation can help.

There is a high chance of developing an under active thyroid. Speak to your doctor about when they will test for this. You usually have a blood test 4 weeks after the treatment. 

Some people lose their sense of taste slightly. This can happen a few weeks after the treatment and should last only a few days. Drinking plenty of water and sucking citrus fruit sweets after the treatment helps to wash out your salivary glands and reduces this effect.


More information about radiotherapy

Find out about

Internal radiotherapy

Internal radiotherapy safety procedures

Thyroid cancer section

Low iodine diet

Thyroid cancer reading list

For general information and support

Contact the Cancer Research UK nurses on freephone 0808 800 4040 (Open 9am to 5pm, Monday to Friday)

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Updated: 4 May 2016