Radiation Therapy for Thyroid Cancer

Radiation therapy is the use of high-energy waves to destroy cells. It stops the ability of cancer cells to grow and divide. Two kinds of radiation therapy are available for treating thyroid cancer. One is delivered internally and the other is delivered externally.

Radioactive Iodine Therapy (RAI Therapy)

RAI therapy uses radioactive iodine. Thyroid tissue naturally absorbs iodine. When it is radioactive it can destroy thyroid cells, including cancer cells. Since it is concentrated in the thyroid it causes little damage to other tissue in the body. RAI may be given as pills or liquid.

It may be used after surgery to destroy any papillary or follicular thyroid cancer cells that were left in the body. This includes cancer in the thyroid or lymph nodes. Thyroid cancer cells that have spread to other areas of the body will also be affected.

Thyroid hormone pills may need to be stopped before the procedure. This will cause a build-up of thyroid stimulating hormone (TSH) in the blood. High TSH levels make it easier for thyroid cells to take in the radioactive iodine.

Side Effects and Management

Side effects of radioactive iodine therapy are temporary and may include:

  • Giving off radiation until it passes out of the body
  • Pain or swelling in areas where the iodine collects
  • Nausea or vomiting
  • Swelling or pain in the neck or salivary glands
  • Dry mouth
  • Dry eyes
  • Loss of smell or taste
  • Slight, but increased risk of leukemia

Men who receive large doses of radioactive iodine may experience lower sperm counts. Rarely, it may lead to male infertility. Women may have irregular periods after RAI. Women are often advised against getting pregnant for up to 1 year after treatment.

Your care team will give specific instructions on how to best manage these side effects.

External Beam Radiation

Radiation therapy may also be delivered in a beam from outside the body. It will be set to give the cancer as much radiation as possible with as little damage to healthy tissue as possible. A radiation oncologist will develop the dose and schedule for treatment needs. It may be used to destroy remaining cancer cells after surgery. It may also be a treatment for people who cannot tolerate surgery. Intensity modulated radiation therapy (IMRT) is a common option for thyroid cancer. The dose can be weakened or strengthened depending on the target tissue.

For anaplastic thyroid cancer, external beam radiation is used in combination with chemotherapy.

In external beam radiation therapy, radiation is produced by a machine positioned outside the body. Short bursts of x-rays are directed at the tumor site. The radiation specialist will direct the radiation beam to affect as much of the tumor as possible.

Radiation of a Tumor

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Side Effects and Management

Radiation therapy affects a smaller area of the body than chemotherapy. This may reduce overall side effects. However, radiation can damage nearby healthy tissue. Side effects of radiation therapy to the neck area may include:

  • Dry mouth
  • Inflammation and irritation of the mouth
  • Difficulty swallowing
  • Hoarse voice

General radiation side effects may include:

Treatments are available to help manage side effects. Sometimes the treatment may be adjusted. The earlier side effects are addressed, the better.



Anaplastic thyroid cancer. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/anaplastic-thyroid-cancer. Updated June 29, 2018. Accessed December 8, 2018.
External beam radiation therapy for thyroid cancer. American Cancer Society website. Available at https://www.cancer.org/cancer/thyroid-cancer/treating/external-beam-radiation.html. Updated April 15, 2016. Accessed November 6, 2017.
Follicular thyroid cancer. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/follicular-thyroid-cancer-21. Updated June 27, 2017. Accessed December 8, 2018.
General information about thyroid cancer. National Cancer Institute website. Available at: https://www.cancer.gov/types/thyroid/patient/thyroid-treatment-pdq. Updated August 18, 2017. Accessed December 8, 2018.
Medullary thyroid cancer. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/medullary-thyroid-cancer. Updated June 29, 2018. Accessed December 8, 2018.
Papillary thyroid cancer. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/papillary-thyroid-cancer. Updated August 15, 2018. Accessed December 8, 2018.
Radioactive iodine (radioiodine) therapy for thyroid cancer. American Cancer Society website. Available at: https://www.cancer.org/cancer/thyroid-cancer/treating/radioactive-iodine.html. Updated April 15, 2016. Accessed November 6, 2017.
Treatment option overview. National Cancer Institute website. Available at: https://www.cancer.gov/types/thyroid/patient/thyroid-treatment-pdq#section/_67. Updated August 18, 2017. Accessed November 6, 2017.
Last reviewed September 2018 by EBSCO Medical Review Board Mohei Abouzied, MD, FACP
Last Updated: 12/29/2020

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