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Preparing for radioactive iodine treatment

Read about what radioactive iodine treatment is, when you have it and how to prepare for it.

What radioactive iodine is

Radioactive iodine treatment is a type of internal radiotherapy. The treatment uses a radioactive form of iodine called iodine 131 (I-131). The radioactive iodine circulates throughout your body in your bloodstream. Thyroid cancer cells pick up the iodine wherever they are in your body. The radiation in the iodine then kills the cancer cells.

Radioactive iodine is a targeted treatment. It is mainly taken up by thyroid cells, having little affect on other cells. The treatment is only suitable for some types of thyroid cancer. It is used for:

  • follicular thyroid cancer
  • papillary thyroid cancer

It can treat the cancer even if it has spread. But if you have one of these types of thyroid cancer, this treatment may not be necessary or suitable for you. You may have a test dose to see if your cancer cells take up iodine, because not all of them do.

When you have it

Radioactive iodine treatment may be given:

  • 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 it was first treated

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

Preparing for radioactive iodine treatment

Before you have radioactive iodine treatment, you may have a man made type of thyroid stimulating hormone called recombinant human TSH (rhTSH) for 2 days. It helps any thyroid cancer cells in the body to take up radioactive iodine. Or, your doctor may ask you to stop taking your thyroid hormone tablets. They call this thyroid withdrawal. 

You stop taking the tablets for 4 weeks if you are taking T4 (thyroxine) or 2 weeks if you are taking T3 (liothyronine). This is because the I-131 works best when the levels of another hormone called TSH (thyroid stimulating hormone) are high. The levels of TSH in your blood start to rise as soon as you stop taking thyroid hormone tablets.

In some situations, your doctors may not ask you to take thyroid hormone tablets until after your surgery and radioactive iodine treatment have finished.

Low iodine diet

Unrestricted food 

You can eat as much of these foods you want as the idoine levels in them is very low:

  • fruits and vegetables including potatoes
  • meat
  • ordinary table salt and sea salt
  • fresh bread
  • rice and dries 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 modertate 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 serve 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)
Last reviewed: 
08 Jun 2018
  • Cancer and its management (7th edition)
    J Tobias and D Hochhauser
    Wiley-Blackwell, 2010

  • Low iodine diet in differentiated thyroid cancer: a review

    J. H. Li and others

    Clincial Endocrinoloogy, 2016, 84 pages 3-12

  • Low Iodine Diet for Preparation for Radioactive Iodine Therapy in Differentiated Thyroid Carcinoma in Korea

    J. H. Chung

    Endocrinology and Metabolism, 2013, Vol 28, No 3, page 157-163

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