Skip to main content

Thyroid cancer and its treatment with radioiodine

This information is for you, the patient, who will be treated with radioiodine, a radioactive form of iodine.

The aim of this information is:

  • to help you to understand what will happen during your stay in the hospital
  • to give you information and instructions to follow while in the hospital and when you go home after your treatment
  • to answer some of the questions most commonly asked by patients about this type of specialised treatment

Why you will receive radioiodine treatment

You will receive radioiodine because your consultant has chosen this as the most appropriate treatment for your thyroid disease. Most of the radioiodine will be absorbed by any remaining thyroid tissue you may have and will influence the function of the thyroid cells. This is the desired and beneficial medical effect of the treatment.

The dose of radioiodine you are receiving means you will have to stay in hospital for your treatment.

Before your treatment

If you are taking thyroid tablets you will need to stop taking them before receiving the radioiodine treatment. Your doctor and/or the Nuclear Medicine Department will tell you when to stop these tablets but once the treatment is over you will be able to start them again.

However, for some patients, your doctor may decide that it is not advisable for you to stop taking your thyroid tablets.  In this case you will have a special injection of Thyrogen on each of the two days before you are treated with radioactive iodine.

All patients need to follow a ‘low iodine’ diet for two weeks before the treatment. Some other medications may interfere with the treatment so you must tell the Nuclear Medicine Department about all medications you are taking. Also, it is not possible to have a treatment within three months of having X-ray or CT tests involving contrast media (an injection of iodine based dye used for some x-ray tests).

Women must not be pregnant when receiving radioiodine treatment and breast feeding must be stopped after radioiodine treatment.

Guidelines to follow in hospital

The best source of additional information on your treatment is your consultant and nuclear medicine staff. This page lists some guidelines for you to follow while you are in hospital and for a short time immediately after your treatment.

While in hospital:

  • you will be confined to your room (but not necessarily to your bed) for approximately one to three days. The duration of your stay in the hospital will depend on how much radioiodine remains in your body
  • you will have your own telephone, TV, DVD player, CD player/radio and your own private bathroom with a shower, toilet and washbasin
  • you will be given disposable cutlery and crockery to use
  • you can bring in books, magazines, CDs and DVDs or anything else to pass the time. We will monitor your belongings for contamination beforeyou are discharged but it is worth bearing in mind that it may be necessary for us to store some items if they are contaminated.

When you go home

You will be given an Instruction Card on your discharge from hospital to guide you for a specified time after your therapy. The instructions will depend on how much radioiodine remains in your body and on your personal situation.

Precautions you may need to take for a short period depending on your personal circumstances:

  • Minimise close contact with adults - the radiation is for your benefit and any exposure other people may receive from you is totally unnecessary
  • Sleep alone
  • It is important that you are not pregnant while you are receiving the radioiodine treatment. If applicable, discuss with your doctor how long you should wait before becoming pregnant after your treatment
  • Avoid close contact with children and pregnant women
  • Do not return to work or visit places of entertainment until an appropriate period of time has elapsed
  • Maintain careful hygiene to avoid spreading contamination to others
  • There may be some restrictions on how you can travel home after treatment (e.g. private car or public transport). These restrictions may also apply for a few weeks after the treatment

Some general information about radioiodine

How does radioiodine work?

The thyroid gland takes up the iodine that enters the body in food and uses this iodine to perform its normal function, which is to make thyroid hormone. Radioiodine is similarly collected by the thyroid gland but the radioactivity destroys the thyroid cells. Since your medical problem is related to the working of these cells, this is exactly the effect required and the very reason you will be given this treatment.

The treatment

The radioiodine that you require will be in a gelatine capsule (very much like an antibiotic capsule) which you will have to swallow with a glass of water. You will not be allowed to eat or drink for two hours after the treatment but after that you should drink as much as possible and eat as normal.

How long does the radioiodine stay in the body?

The radioiodine from your treatment will remain in your body only temporarily. Most of the radioiodine not taken up by your thyroid gland will be eliminated during the first two to three days after your treatment. We recommend that you drink plenty of fluid during these days.

Radioiodine leaves your body primarily in your urine, but very small amounts may leave in your saliva and sweat (this is why you have a separate toilet and cutlery). It is also advisable to bring lemon drops or other mouth-watering sweets with you as sucking these will help minimise the amount of radioiodine that goes into your salivary glands.

The amount of radioiodine remaining in your thyroid tissue is responsible for the desired medical effect. However, this amount also decreases rapidly. This means that the possibility of radiation exposure to you and others is reduced with time. In a fairly short time after you go home the amount of radioiodine remaining in your body becomes insignificant.

How can you reduce radiation exposure to others?

The amount of radioiodine in your body during the first few days of your treatment is quite large. Although there is no evidence that the radiation from this amount of radioiodine will cause harm for other people, it is sensible to take steps to minimise exposure, no matter how small. We therefore ask you not to have any visitors for the first two days of your treatment and no children or pregnant women are allowed at any point during your stay.

If you take some simple precautions for a short period of time after leaving hospital, you can reduce or eliminate the possibility of radiation exposure to members of your household and other people you may come into close contact with.

Our instruction card will guide you on these matters.

There are three basic principles to remember:


The greater the distance you are from others, the less radiation they will receive. Even an increase in distance of a few feet will greatly reduce the exposure, so try not to remain in close contact with others for longer than is necessary.


Radiation exposure to others depends on how long you remain close to them. You should try to minimise the time spent in close contact with others.


Good hygiene minimises the possibility that other people will be contaminated with the radioiodine that leaves your body. Since most of the radioiodine leaves your body in your urine, good toilet hygiene and careful and thorough washing of your hands will reduce the possibility of contamination.

The easiest way to remember these principles is to imagine how you behave around others when you have a bad cold.


If you have any further questions about your treatment please feel free to ask your doctor or the medical physics staff in Nuclear Medicine or alternatively make a note and we will answer them when you attend the hospital.

Last reviewed: 14 June 2023