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Radioactive iodine treatment for thyroid cancer

Radioactive iodine treatment is a type of internal radiotherapy for thyroid cancer. It 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 will not affect other body cells because only thyroid cells pick up iodine. The treatment is only suitable for papillary and follicular thyroid cancers but can treat them even if they have spread. If you have one of these types of thyroid cancer, this treatment may not be necessary or suitable for you. Your doctor may carry out a test to see if your cancer cells pick up iodine or not.

Having the treatment

To have the treatment, you go into hospital for a few days. You usually have the iodine as a drink or capsule. You won’t be able to eat or drink for a couple of hours so that your body can absorb the iodine. After that, you can eat normally. The treatment will make you slightly radioactive and you will stay in a single room for a few days. You should try to drink plenty of fluids to help flush the radioactive iodine out of your system. Once the radiation level is low enough, you will be able to go home.
 

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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 doesn't affect other body cells, because only thyroid cells take up the iodine. The treatment is only suitable for some types of thyroid cancer. It is used for

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.

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, if needed, it can be repeated every 3 months 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 a few weeks. 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

You will be asked to start eating a low iodine diet 2 weeks before you have radioactive iodine treatment. You need to have a low iodine diet because too much iodine in your body can stop the treatment working so well. 

You should not have

  • Iodised table salt or sea salt
  • Cough medicine
  • Fish and seafood
  • Vitamin supplements that say they contain iodine

Dairy products contain some iodine, so you need to cut down on eggs, cheese, milk and milk products. You don't have to cut these out altogether but have as little as you can.

You should also cut out any food coloured pink with the additive E127. So, do not eat

  • Spam or salami
  • Tinned strawberries
  • Glacé cherries
  • Pink pastries or sweets (look on the labels for E127)
 

Having the treatment

To have radioactive iodine treatment, you go into hospital. You will be looked after in a single room. The treatment makes you slightly radioactive for a few days. Your sweat and urine will be radioactive during this time. Your sheets may be changed every day and the hospital staff may ask you to flush the toilet more than once after you have used it.

You usually have the radioactive iodine as a drink or capsule. Your nurse will ask you not to eat or drink for a couple of hours afterwards so that your body can absorb the iodine. After that, you can eat normally. You need to drink a lot to flush the radioactive iodine out of your system.

You will have to stay in your single room for a few days until your radiation levels have fallen. A radiation monitor (Geiger counter) may be used to check your levels of radioactivity or test anything that is taken out of your room. Some of your possessions may be kept on the ward for a couple of days if they show any radioactivity. After that time, they will be safe again and the nurses will give them back to you to take home.

After a few days, you may have a scan. The scan shows where in the body the radioactivity has been taken up.

 

Protecting other people from the radioactivity

Being in a room on your own (isolation) protects other people from radiation. Pregnant women and children will not be allowed into your room. Other visitors will only be able to stay for a short time each day. And the amount of time the staff will be allowed into your room is limited. It is important that you know that you are not at any risk from the radiation. The staff in the hospital give this treatment to many people. So, the amount of radiation they are exposed to has to be limited.

 

Coping with isolation

Being looked after in a single room can feel lonely. Some people find it frightening. It can help to talk to the nurses about your worries. They can reassure you.

Taking in some of your personal things can make the room feel more homely. Books, photographs and an ornament or two can brighten it up. You can also take in a mobile phone, laptop, electronic tablet or music player to make the time pass more enjoyably and keep in touch with friends and family.

 

After radioactive iodine treatment

A few days after the treatment your doctors will check to see if the radioactivity has dropped to a safe level. Once it has, you will be able to go home. You may be told that you shouldn't be in contact with children, pregnant women or breastfeeding mothers for a short time. Check this with the staff before you go, so that you're sure about what you can and can't do. Ask them how long you need to take precautions. 

If you had to stop taking your thyroid hormone tablets, your nurse will tell you when you can start to take them again. Usually, this is 3 days after your treatment.

Your doctors may ask you to have a radioactive iodine scan a few months after the treatment to see if it shows any thyroid cells left in your body. If there are any thyroid cells, you may have further doses of the radioactive iodine treatment. Some hospitals use the levels of particular thyroid hormones in your blood combined with an ultrasound of the neck to check whether you need further treatment.

 

Possible side effects

The side effects of radioactive iodine treatment vary depending on your age, whether you have other medical conditions and the dose of radioactive iodine you have. Some people may have one or more of the following side effects.

Possible short term side effects include

  • Inflammation of the salivary glands (where your spit is made) – you can have painkillers if needed
  • You may also have a dry mouth and your nurse can give you artificial saliva
  • Inflammation of the mouth – you can have anti inflammatory mouthwash
  • Short term changes to taste and smell – this usually resolves within 4 to 8 weeks
  • Nausea which usually lasts a couple of days – you can have anti sickness medicine for this
  • Neck pain and swelling – this is not very common and you can have anti inflammatory medicine to reduce the swelling and pain

Possible long term side effects include

  • Blockage of the tear ducts and you may have a lot more tears than normal – this can be treated by unblocking the tear ducts
  • Temporary reduction in testosterone in men
  • Temporary stopping of periods or heavier periods in women
  • Temporary disturbance in how your bone marrow works – your doctor will monitor this
  • Lung problems – your doctor will monitor this and you will have treatment, if necessary
  • Second tumours – these are rare, but if you are concerned you can ask your doctor or clinical nurse specialist to discuss this with you
 

Travelling after radioactive iodine treatment

If you are planning to travel abroad you should be aware that recent treatment with radioactive iodine may set off radiation alarms at airports. This could happen up to 12 weeks after your treatment. So, to avoid problems make sure you take a certificate from the hospital or a letter from your doctor telling about the treatment you have had.

 

More about radioactive iodine treatment

There is detailed information about radioactive iodine treatment and the safety precautions in the radiotherapy section.

You can phone the Cancer Research UK nurses on freephone 0808 800 4040. The lines are open from 9am to 5pm, Monday to Friday. They will be happy to answer any questions that you have.

Our general organisations page gives details of people who can provide information about radiotherapy. Some organisations can put you in touch with a cancer support group. Our cancer and treatments reading list has information about books, leaflets and other resources about radiotherapy treatment.

If you want to find people to share experiences with online, you could use Cancer Chat, our online forum.

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Updated: 14 May 2014