Radioactive Iodine Therapy

June 15, 2024 
This page was reviewed under our medical and editorial policy by Sasan Fazeli, M.D., assistant clinical professor in the Department of Diabetes, Endocrinology and Metabolism, and Karen Tsai, M.D., assistant clinical professor in the Department of Diabetes, Endocrinology and Metabolism, City of Hope® Cancer Center Duarte.

Radioactive iodine therapy, also called RAI therapy, is used to treat certain types of thyroid cancer. It may be used as a thyroid cancer treatment because the thyroid’s role is to absorb nearly all iodine in the body. When RAI is absorbed by the thyroid, it allows the radiation to destroy remaining thyroid cells and any cancer cells, leaving the rest of the body mostly unaffected.

RAI may be used as a thyroid cancer treatment after surgery (such as total thyroidectomy) to help ensure all cancer cells have been destroyed.

What Is Radioactive Iodine?

A small amount of radioactive iodine is used to scan for residual thyroid cancer. RAI therapy uses a much larger radioactive iodine dose to destroy thyroid cancer cells, and it is often used to treat papillary, follicular and oncocytic (Hürthle cell) thyroid cancers that have spread to the lymph nodes or other areas. It is not used to treat medullary thyroid cancer (MTC) or anaplastic thyroid cancer (sometimes called undifferentiated thyroid cancer) because these cancer cells do not absorb the iodine.

When getting RAI therapy, isolation in a proper way needs to be arranged, and a radiation safety consultation is typically helpful.

How to Prepare for RAI Therapy

A high blood level of thyroid-stimulating hormone (TSH) is required for the thyroid tissue and cancer cells to absorb the radioactive iodine and to make RAI treatment successful. That’s why the thyroid cancer care team helps patients prepare for this therapy by taking steps to raise their TSH levels. This may be done in one of two ways:

Stop taking thyroid hormone pills for several weeks (withdrawal). This causes the body’s pituitary gland to release more TSH to combat the low thyroid hormone levels. This will be temporary, but patients may notice temporary symptoms of low thyroid hormone (hypothyroidism) during this time, such as:

  • Fatigue
  • Unintentional weight gain
  • Depression
  • Constipation
  • Achy muscles
  • Difficulty concentrating
  • Cold intolerance

Get thyrotropin (Thyrogen®) shots. This injection may eliminate the need to withhold thyroid medications for a long period. Thyrotropin may be given by daily injection in the clinic for two consecutive days before the RAI therapy.

Whether patients get to stop the thyroid hormone pills or get the thyrotropin shot, they’ll need to follow a low-iodine diet for two weeks before RAI therapy. A low-iodine diet means avoiding foods such as iodized salt, cereals, some breads and other grains, as well as seafood, seaweed, beef, poultry, eggs, dairy and soy products. It is also recommended to avoid any foods or candies that have the additive red dye #3, because it contains iodine. The care team may recommend that the patient meets with a nutritionist for a consultation about what to eat and what to avoid.

The Procedure

RAI therapy is usually given in the nuclear medicine department of a hospital. It’s usually given in capsule form. This is often a one-time dose that may be given with medications to control nausea.

Patients who receive large RAI therapy doses typically stay in isolation for two to three days. Length of stay and isolation are dependent on the dose of RAI therapy and how quickly the radiation passes through the body. After RAI treatment, the body gives off radiation, so hospitals have patients stay in isolation rooms.

If the patient is sent home, he or she will be instructed to limit exposure to others. This may include:

  • Avoiding public transport on the way home
  • Staying away from those pregnant or trying to become pregnant for a short period
  • Isolating from family members at home and using a separate bed, shower and restrooms for a short period
  • Using separate utensils for a short period
  • Washing clothing separately for a short time
  • Increasing fluid intake to help flush out the radioactive iodine.

Most of the radiation typically resolves within a few days.

Radioactive Iodine Side Effects

The thyroid cancer care team will discuss short- and long-term side effects with the patient and explain which side effects should be reported immediately.

Short-term side effects may include:

  • Nausea and vomiting (usually on the day of treatment)
  • Tenderness and swelling in the neck
  • Dry mouth
  • Swollen salivary glands (gum or hard candy may provide relief)
  • Changes in taste
  • Dry eyes

Long-term effects vary, but may consist of:

  • Lower sperm counts in men who have had high-dose or multiple treatments, or, in rare cases, infertility
  • Irregular menstrual cycles for up to one year in women (which is why doctors recommend not becoming pregnant for up to nine months after RAI administration)
  • A slightly higher risk of developing other cancers in the future, including leukemia other solid cancers (uterine, lung, stomach, salivary gland and breast)

Life after Treatment

After RAI for thyroid cancer, medical follow-ups are necessary. The cancer care team will check the patient regularly for any sign that cancer has returned and will help manage side effects, track hormone levels and monitor overall health.

The low-iodine diet should be continued for one to two days following RAI. A soft, moist diet may be recommended to alleviate sore throat, dry mouth and trouble swallowing. Dry or hard foods such as pretzels and chips should be avoided until the throat feels better.

In those who had thyroid hormone medication held in preparation for RAI treatment, instructions on how to resume thyroid hormones will be given to patients, and blood tests will be performed periodically to monitor thyroid hormone levels.

In most patients, thyroid cancer tumor markers and imaging will be evaluated following cancer treatment to monitor for recurrence of thyroid cancer. Interval follow-up will be dependent on the patient’s treatment response.

References
References
  • Radioactive iodine (radioiodine) therapy for thyroid cancer. American Cancer Society, February 18, 2023). 
    https://www.cancer.org/cancer/types/thyroid-cancer/treating/radioactive-iodine.html

  • Thyroid cancer: follow-up care. American Society of Clinical Oncology, August 2023. 
    https://www.cancer.net/cancer-types/thyroid-cancer/follow-care

  • Thyroid cancer: types of treatment. American Society of Clinical Oncology, August 2023. 
    https://www.cancer.net/cancer-types/thyroid-cancer/types-treatment#radioactive-iodine-therapy

  • Thyroid cancer treatment (PDQ®) – health professional version. National Cancer Institute, April 11, 2024. 
    https://www.cancer.gov/types/thyroid/hp/thyroid-treatment-pdq#_920

  • Low iodine diet. American Thyroid Association. 
    https://www.thyroid.org/low-iodine-diet/

  • Low iodine diet. Thyroid Cancer Survivors Association, March 14, 2023. 
    https://www.thyca.org/download/document/229/Cookbook1pgEng.pdf

  • Rosol TJ, Gröne A (2016). Jubb, Kennedy & Palmer's Pathology of domestic animals: Volume 3 (Sixth Edition). Pages 269-357.e1. 
    https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/erythrosine