Radioactive Iodine

Thyroid cancer patients with papillary or follicular thyroid cancer often receive a dose of radioactive iodine around four to six weeks after their surgery in an attempt to destroy (ablate) any remaining thyroid cells in their bodies.
The purpose of radioactive iodine is to:
  • increase survival by reducing the chance of the thyroid cancer recurring,  
  • increase the ability to find a cancer recurrence in the future, and  
  • enhance the effectiveness of future radioactive iodine treatments if needed. 
How Does Radioactive Iodine Work?

Iodine is taken up by the thyroid gland and most thyroid cancers. When the cells take up iodine, they also take up radioiodine or iodine-131, which is a radioactive form of iodine. Iodine that is radioactive can be used to find and treat thyroid cancer. 

Radioactive iodine is one of the oldest and best forms of cancer treatment for any thyroid cancer that will take up radioiodine. It destroys cancer cells.
Radioactive iodine is usually given as a capsule. You do not need to remain in the hospital after this treatment.
What Is a Metastatic Survey (Radioactive Iodine Scan)?

This survey is also done in Nuclear Medicine for patients with thyroid cancer.  Most often it is done after thyroid surgery and ablation, and again at times after that as needed. It is used to find out if there is any spread of cancer (metastases) to other parts of your body.
For the survey, you will be given a small amount of radioactive iodine to drink.  It will travel to any thyroid tissue and to most thyroid metastases. You will return to Nuclear Medicine after two or more days, and images of your body will be made. These will show how much thyroid tissue is left in your neck and whether or not there is any spread of the cancer.
How do I Prepare for a Metastatic Survey?

If you have been taking any thyroid hormone pills, you will have to stop them about a month before the survey, since they will impact the test. You will be told when you should start taking these pills again after taking the radioiodine and scan.

When the survey is scheduled, you will also be scheduled to have a TSH blood test done about two days before the survey. A sample may also be taken to measure serum thyroglobulin.

You may be asked to maintain a low iodine diet for about ten days in order to allow the test to work better. To do this, you should avoid milk products, seafood, kelp, and many seasonings (especially salt which has had iodine added).  Most fruits, vegetables, meats, and breads (or cereals) that have not been processed are fine.

Please tell us if you have had an x-ray procedure with contrast in the last few weeks.  You must not be pregnant or breast feeding when you receive radioiodine.  You should not plan to become pregnant in the next six months.

How Should I Take Care of Myself after I Receive Radioiodine?

The radioiodine that is not taken up will leave your body within about two days.  Most is lost through your urine, but some is also released in saliva, sweat, and stool.  In order to help remove the extra radioactivity, you should drink extra fluids and empty your bladder often (about every hour or so) for the first day. 

During the first two days after the dose, drink plenty of juices, water, and milk.  You should try to have at least one bowel movement each day.  Add fiber and prune juice to your diet. You may need a laxative if you are having trouble with bowel movements. You might be advised to take lemon candies to stimulate saliva secretion about 6-10 hours after your radioiodine drink.

What about Exposure to Other People?

The dose of radioiodine used to perform a metastatic survey or a thyroid ablation is usually small. People around you are at very low risk from the radiation. There are things that you can do in the first two to three days to lessen the risk for others. 
  • Do not return to work until the next day.
  • Limit your time in public places.
  • Do not travel by airplane or prolonged car trips for two days.
  • Maintain an arm's length distance from other people if you will be with them for long periods of time.  We will demonstrate this to you; radiation exposure decreases rapidly with distance and even an arm's length distance reduces doses that other people may receive by 10-30 fold.
  • Flush the toilet twice after using it.  Rinse under the rim of the toilet with a brush and reflush. If possible, use a different toilet from others.
    Avoid sharing of eating utensils.  After use, you can wash utensils as usual.
  • Sleep in a separate bed for 1-2 days.
  • Avoid close contact with children and pregnant women.
  • If you think you are pregnant, inform your doctor because radioiodine should not be given to pregnant women.  After receiving radioiodine, you should avoid getting pregnant for about six months.
  • Radioiodine will show up in breast milk.  Inform your doctor if you are breast-feeding.