Radioactive iodine treatment

Radioactive iodine (RAI) is also known as I131 and is a type of radioisotope treatment. Radioisotopes are radioactive substances given in a pill that you swallow. Although RAI spreads through the body, it is mainly absorbed by thyroid cells or thyroid cancer cells. RAI kills these cells while leaving other body cells relatively unharmed.

You may be given RAI to destroy tiny amounts of remaining cancer cells or healthy thyroid tissue left behind after surgery. It is usually recommended for papillary or follicular thyroid cancers that have spread to the lymph nodes or that have a higher risk of coming back after surgery. RAI doesn’t work for medullary or anaplastic thyroid cancer because these types do not take up iodine.

Learn more about:

• When to have RAI treatment
• Preparing for radioactive iodine treatment
• Having radioactive iodine treatment
• Safety precautions in hospital and at home
• Side effects of radioactive iodine treatment

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When to have RAI treatment

RAI is generally not given until some weeks after surgery, once any swelling has gone down. This is because swelling can affect the blood flow and stop the RAI circulating well.

It is not safe to have RAI treatment if you are pregnant or breastfeeding, so treatment may be delayed. RAI may be given up to six months after surgery. Ask your doctor for more information.

Preparing for radioactive iodine treatment

Limiting foods high in iodine

A diet high in iodine makes RAI treatment less effective. You will need to start avoiding high-iodine foods two weeks before treatment. This includes foods such as seafood, iodised table salt and sushi. Your treatment team will give you more detailed instructions.

Discussing imaging scans

CT scans and other imaging scans sometimes use an injection of a dye called contrast to make the images clearer. This contrast can interfere with how well RAI works, so it is important to tell your doctor if you have had a scan using contrast in the month before RAI treatment.

Raising TSH levels

For RAI treatment to work, you will need a high level of TSH in your body. There are two ways to increase your TSH levels:

• You may be prescribed a synthetic type of TSH called recombinant human thyroid-stimulating hormone (rhTSH), also known by the brand name Thyrogen. You will need two injections of Thyrogen, usually into the muscle in your buttock, with the first injection two days before RAI treatment, and then the second injection the day before. Thyrogen allows you to continue taking your thyroid hormone replacement medicine.
• You can stop taking your thyroid hormone replacement medicine for a few weeks. You will have a blood test before RAI treatment to check that the TSH levels have risen enough. In some people, stopping their hormone replacement medicine causes symptoms of hypothyroidism. These symptoms may affect your ability to concentrate, so check with your doctor whether it is safe to drive and use heavy machinery.

The option recommended for raising your TSH levels will depend on your stage of disease and what is suitable for you.

For more details, see Ways to raise TSH levels, and talk to your specialist.