Thyroid & Parathyroid Problems

Radioactive Iodine (RAI) Treatment

What is radioactive-iodine and how does it work?

Iodine is one of the key building blocks that the thyroid gland uses to make the thyroid hormones tri-iodothyronine (T3) and thyroxine (T4). To do this the thyroid absorbs dietary iodine from the bloodstream. This is controlled by another hormone Thyroid Stimulating Hormone (TSH).

The thyroid gland (and thyroid cancer cells) are the only tissues in the body that take up iodine so strongly and so it makes sense that if you want to get drugs to target thyroid cells it would be a good idea to use iodine as the carrier. Radioactive iodine (RAI) is as you might guess is a radioactive variant of iodine and is selectively taken up by thyroid tissue where it delivers its radiation dose destroying thyroid cells.

When is radioactive iodine used?

There are 3 main reasons that your thyroid specialist may recommend RAI therapy:

In the treatment of Grave's Disease. Here RAI is used in relatively low doses to try to reduce the overactivity of the thyroid gland. One of the main side effects of this is that the gland will sometimes become underactive.
After surgical removal of a thyroid cancer (Remnant Ablation) - the most common reason for RAI therapy.
For the treament of thyroid cancer that is not easily removed by surgery. Rarely thyroid cancers may spread to places where they are not easily removed by surgery for example to the lungs. High doses of RAI may be necessary to try and stop the cancer from growing.

What is Remnant Ablation?

Remnant ablation is RAI given after removal of the thyroid gland (total thyroidectomy) for thyroid cancer. Even with the most careful operation it is not usually possible for your surgeon to remove all of the thyroid tissue from the neck and a small amount may be left behind (the thyroid remnant). This may contain some cancer cells; some thyroid cancer cells may also have spread into the circulation and not be removable by surgery.

RAI remnant ablation is given after the surgery to “mop up” any remaining thyroid cells. As only thyroid cells absorb radioactive iodine this is an excellent way of targeting radiation treatment where it is most needed.

Why is it used?

It is an ideal way of targeting radiation therapy at thyroid cancer cells wherever they may be lurking. Destroying all remaining thyroid tissue also allows your doctor to check that the cancer doesn’t come back by measuring a tumour marker called thyroglobulin (TG) in your bloodstream.

Thyroglobulin is only made by thyroid or thyroid cancer cells and so if you have your thyroid gland removed and RAI remnant ablation it should not be possible to measure any thyrogloblin in your blood. If your thyroglobulin levels begin to rise this may be an early sign that the thyroid cancer has returned and that further treatment is required.

Who should have Remnant Ablation

RAI is an extremely effective way of treating some of the most common forms of thyroid cancer (see Well Differentiated Thyroid Cancers). It is not an effective treatment for some other forms of thyroid cancer where the cells no longer are able to take up iodine in the same way (None Differentiated Thyroid Cancers, Anaplastic Thyroid Cancers, Medullary Thyroid cancers).

It is the standard treatment for thyroid cancer following total thyroidectomy. It is not a substitute for surgery and it is not possible to give RAI where large amounts of thyroid tissue are left behind (eg Hemithyroidectomy).

Does every patient who has thyroid cancer need Remnant Abalation?

No. Some patients with small tumours (less than 1.5cm), who are young and at low risk of cancer recurrence are thoroughly treated by surgery alone and do not require radioactive iodine treatment.

How is it given?

You will be admitted to a special ward in the hospital where radio-isotope treatments are given. You will get your own room but will not be able to leave for 2-3 days as you will be radioactive. The radioactive iodine medicine is given as either pills or a liquid. You may also need to have 2 injections of a medicine called thyrotropin or Thyrogen which increases TSH production form your pituitary gland and makes thyroid cells take up the radioiodine. You will also have a couple of scans whilst you are in the hospital to assess the success of the treatment.

Are there any special precautions?

Yes, before your treatment you will need to have a low iodine diet, so no sushi or fish. Your will need to stop breastfeeding at least 8 weeks before any radioiodine treatment and you will not be able to breast feed afterwards.

Are there any side effects?

Side effects are usually mild but can be a dry mouth, pain in the saliva glands and rarely swelling in the neck.

Will I still be able to have children?

Yes, but radioiodine (especially repeated doses) does carry an increased risk of fetal abnormalities. It is very important that you do not get pregnant (or get anyone else pregnant if you are a man) for 6 months after radioiodine treatment.