Thyroid Cancer: Radioactive Iodine Therapy

March 21, 2017

Thyroid Cancer: Radioactive Iodine Therapy

What is radioactive iodine therapy?

Radioactive iodine therapy uses a form of iodine that sends out radiation to treat thyroid cancer. Radioactive iodine is also called I-131.The thyroid gland absorbs nearly all the iodine in the blood. So, when a large dose of radioactive iodine is taken, the radiation can destroy the thyroid gland and thyroid cancer cells with little effect on the rest of the body.

When might radioactive iodine therapy be used?

After you've had surgery for thyroid cancer, you may have treatment with radioactive iodine (I-131). I-131 might also be used to treat thyroid cancer that has spread beyond the thyroid gland. The goal of this treatment is to target and kill any remaining thyroid cells or thyroid cancer cells anywhere in your body.

I-131 may be used to slow the growth of papillary and follicular thyroid cancer. It is not used to treat medullary or anaplastic thyroid cancer, because these types do not take up iodine.

You may be given a small test dose before the actual treatment to make sure that the I-131 is absorbed by the thyroid tumor.

Special precaution if you are or might be pregnant

Radioactive iodine can destroy the thyroid in an unborn baby. Be sure to tell your doctor if you might be pregnant before you have this treatment.

Your doctor may advise you to wait 6 months to a year after radioactive iodine therapy before you try to get pregnant.

How is radioactive iodine therapy given?

Radioactive iodine is taken as a pill or liquid that you swallow. It's absorbed into your blood and travels through the blood to collect in thyroid cells.

Radioactive iodine therapy is most effective if you have high blood levels of thyroid stimulating hormone (TSH). This causes thyroid cells in the body, including thyroid cancer cells, to take up the iodine. Before treatment, you may be given a medicine to raise your TSH levels. TSH levels can also be raised by not taking thyroid hormone after surgery for a few weeks. But this can cause side effects such as feeling tired and depressed. 

You may be instructed to stop taking thyroid hormone replacement medicines and follow a low iodine diet for a few weeks before treatment.

What to expect after getting radioactive iodine therapy

You need to take a few precautions after this type of treatment. For instance, you must limit contact with other people for a few days after taking radioactive iodine. That’s because your body will give off radiation for some time after the treatment (about 2 to 5 days). You may need to stay in the hospital during this time. Your doctor may also suggest that you drink a lot of fluids. Fluids will help flush the radioactive iodine out of your system.

Your doctor may suggest that you flush the toilet twice after urinating. This helps rid the toilet of radioactive material.

Most radiation from I-131 is gone in about 1 week. Ask your doctor about other precautions you should take to protect others after treatment and how long you need to take them.

You also need to know that high doses of I-131 kill normal thyroid cells, which make thyroid hormone. After radioactive iodine therapy, you will need to take thyroid hormone pills to replace the natural hormone that your body can no longer make on its own.

Be sure to ask your treatment center to give you a note documenting your radioiodine treatment if you plan to be traveling by air. The radioiodine will be detectable for several days by radiation detection machines.

What are the side effects of radioactive iodine therapy?

Radioactive iodine therapy does not often cause side effects right away. Some people may have neck pain, nausea, dry eyes, and dry mouth.

Radioiodine decreases tear production. So if you wear contact lenses, don’t use them for several days after this treatment.

In rare cases, men may become infertile. Radioactive iodine may have an effect on women's ovaries. Irregular periods have been seen for up to 1 year after treatment.

This therapy may also carry a very small risk of leukemia later in life. More research is needed to determine exactly how much the risk is increased.

Working with your healthcare provider

Make sure you understand the precautions you need to take. Talk with your healthcare providers about what signs of problems you need to look for and when to call them. Also be sure you have a prescription for replacement thyroid hormones and you know how to take this medicine.

It may be helpful to keep a diary of your side effects. Write down physical, thinking, and emotional changes. A written list will make it easier for you to remember your questions when you go to your appointments. It will also make it easier for you to work with your healthcare team to make a plan to manage your side effects.



March 21, 2017


Grammatikakis, I. Successful pregnancy after radiotherapy with 131I for differentiated thyroid cancer, Clinical Experimental Obstetrics and Gynecology (2010); 37(4); pp. 328-330

Reviewed By:  

Hurd, Robert, MD,Stump-Sutliff, Kim, RN, MSN, AOCNS