Radioactive Iodine (Radioiodine) Therapy for Thyroid Cancer

Your thyroid gland absorbs nearly all of the iodine in your body. Because of this, radioactive iodine (RAI, also called I-131) can be used to treat thyroid cancer. The RAI collects mainly in thyroid cells, where the radiation can destroy the thyroid gland and any other thyroid cells (including cancer cells) that take up iodine, with little effect on the rest of your body. The radiation dose used here is much stronger than the one used in radioiodine scans, which are described in Tests for Thyroid Cancer.

This treatment can be used to ablate (destroy) any thyroid tissue not removed by surgery or to treat some types of thyroid cancer that have spread to lymph nodes and other parts of the body.

Radioactive iodine therapy helps people live longer if they have papillary or follicular thyroid cancer (differentiated thyroid cancer) that has spread to the neck or other body parts, and it is now standard practice in such cases. But the benefits of RAI therapy are less clear for people with small cancers of the thyroid gland that do not seem to have spread, which can often be removed completely with surgery. Discuss your risks and benefits of RAI therapy with your doctor. Radioactive iodine therapy cannot be used to treat anaplastic (undifferentiated) and medullary thyroid carcinomas because these types of cancer do not take up iodine.

Preparing for RAI therapy

For RAI therapy to be most effective, you must have a high level of thyroid-stimulating hormone (TSH or thyrotropin) in the blood. This hormone is what makes thyroid tissue (and cancer cells) take up radioactive iodine. If your thyroid has been removed, there are a couple of ways to raise TSH levels before being treated with RAI:

  • One way is to stop taking thyroid hormone pills for several weeks. This causes very low thyroid hormone levels (hypothyroidism), which makes the pituitary gland to release more TSH. This intentional hypothyroidism is temporary, but it often causes symptoms like tiredness, depression, weight gain, constipation, muscle aches, and reduced concentration. 
  • Another way is to get an injection (shot) of thyrotropin (Thyrogen), which can make withholding thyroid hormone for a long period of time unnecessary. This drug is given daily for 2 days, followed by RAI on the 3rd day.

Most doctors also recommend that you follow a low iodine diet for 1 or 2 weeks before treatment. This means avoiding foods that contain iodized salt and red dye #3, as well as dairy products, eggs, seafood, and soy.

Risks and side effects

Your body will give off radiation for some time after you get RAI therapy. Depending on the dose of radioiodine used and where you are being treated, you might need to be in the hospital for a few days after treatment, staying in a special isolation room to prevent others from being exposed to radiation. Some people may not need to be hospitalized. Once you are allowed to go home after treatment, you will be given instructions on how to protect others from radiation exposure and how long you need to take these precautions. These instructions may vary slightly by treatment center. Be sure you understand the instructions before you leave the hospital.

Short-term side effects of RAI treatment may include:

Chewing gum or sucking on hard candy may help with salivary gland problems.

Radioiodine treatment also reduces tear formation in some people, leading to dry eyes. If you wear contact lenses, ask your doctor how long you should keep them out.

Men who receive large total doses of radiation because of many treatments with RAI may have lower sperm counts or, rarely, become infertile. Radioactive iodine may also affect a woman’s ovaries, and some women may have irregular periods for up to a year after treatment. Many doctors recommend that women avoid becoming pregnant for 6 months to a year after treatment. No ill effects have been noted in the children born to parents who received radioactive iodine in the past.

Both men and women who have had RAI therapy may have a slightly increased risk of developing leukemia in the future. Doctors disagree on exactly how much this risk is increased, but most of the largest studies have found that this is an extremely rare complication. Some research even suggests the risk of leukemia may not be significantly increased.

Talk to your health care team if you have any questions about the possible risks and benefits of your treatment.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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Last Medical Review: March 14, 2019 Last Revised: March 14, 2019

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