Preparing for radioactive iodine treatment for thyroid cancer

Radioactive iodine treatment is a type of internal radiotherapy. It is a useful treatment for some types of thyroid cancer.

Before you start the treatment, your doctor might ask you to prepare for treatment. This is to help any thyroid cancer cells in your body to take up the radioactive iodine. You might:

• have an injection or stop your thyroid hormone tablet to increase your levels of thyroid stimulating hormone
• follow a low iodine diet before treatment

What is radioactive iodine treatment?

The thyroid gland absorbs and stores most of the iodine in your body. It gets iodine from certain foods and uses this to make essential thyroid hormones.

Radioactive iodine treatment is a type of internal radiotherapy. It uses a radioactive form of iodine called iodine 131 (I-131). The radioactive iodine circulates through your body in your bloodstream. The thyroid gland cells take up the radioactive iodine but it has little effect on other cells.

The thyroid cells take in the iodine and get a very high dose of radiation. This destroys the thyroid cells and any cancer cells.

When do you have radioactive iodine?

Radioactive iodine is only suitable for some types of thyroid cancer. This includes follicular and papillary thyroid cancer. Thyroid cancer cells can pick up radioactive iodine, even if they have spread to other parts of the body. So it can be a treatment for thyroid cancer even if it has spread. 

But radioactive iodine might not be necessary or suitable for everyone with these types of thyroid cancer. Not all cancer cells take up the iodine. You might have a test dose to see if your cancer cells do.

You might have radioactive iodine treatment:

• after surgery, to kill any cancer cells that may have been left behind
• to treat thyroid cancer that has spread
• to treat thyroid cancer that has come back after treatment

You may only need to have this treatment once. But you can repeat it every 3 months if needed, until there is no sign of any thyroid cancer on your scans.

Before your radioactive iodine treatment

For your treatment to work, one of the hormone levels in your body needs to be high. This hormone is called thyroid stimulating hormone or TSH. A high level of TSH helps any thyroid cancer cells in the body to take up radioactive iodine.

To increase the levels of TSH, your doctor will ask you to do one of the following:

• have an injection of a man-made TSH called recombinant human TSH (rhTSH) once a day for 2 days
• stop taking your thyroid hormone tablets a few weeks before treatment (thyroid withdrawal)

Your healthcare team will explain what you need to do and what is going to happen. They will also let you know when to re-start your hormone tablets if you stopped taking them.

Low iodine diet

You might need to have a low iodine diet for a few weeks before you have your treatment. This prepares the thyroid cells so that they can absorb the radioactive iodine. All food and drink contains some iodine.  A low iodine diet means that you should avoid foods that have a high level of iodine in them.

Foods you are allowed 

You can eat the following foods because they contain very low levels of iodine:

• fruits and vegetables including potatoes
• cooked green vegetables
• meat
• ordinary table salt and sea salt
• fresh bread
• rice and dried pasta
• non dairy spreads such as Vitalite, Pure and non dairy Flora
• olive oil, vegetable oils and nut oils
• water, soft drinks, fizzy drinks, fruit juices and alcoholic drinks
• tea and coffee without milk
• milk substitutes such as coconut, rice, almond and soya milk avoid ones that contain an ingredient called carrageenan (as this comes from seaweed)
• dark and plain chocolate that is 70% cocoa or more
• crisps

Restricted food 

You can eat a small amount of these food items as they have a moderate amount of iodine:

• milk - about 5 - 7 teaspoons a day (25 ml)
• butter - a teaspoon (5 g) each day
• cheese - 25 g (1 ounce) per week
• dairy products such as yoghurt and dairy ice cream - 1 portion per week
• 1 egg each week
• products that contain eggs such as mayonnaise, custard, fresh egg pasta, egg fried rice, Yorkshire pudding, pancakes

Food to avoid

You shouldn't eat these foods as they have high levels of iodine:

• fish, seafood, seaweed, kelp and laverbread
• raw green vegetables such as spinach and broccoli
• cakes and biscuits made with eggs or butter
• milk chocolate and white chocolate
• take away foods, fast foods and restaurant food as their ingredients aren't known and might contain iodine
• iodised salt and Pink Himalaya salt that has come from outside the UK
• vitamins and mineral supplements, nutritional supplements and cough mixtures (unless prescribed by your medical team, for example vitamin D)

You can return to your normal diet after you have had your treatment.

Pregnancy and breastfeeding

Tell your doctor if you think you may be pregnant. You should not have this treatment during pregnancy.

Talk to your doctor if you are breastfeeding. You will need to stop breastfeeding before you have treatment with radioactive iodine.