External Beam Radiation Therapy for Thyroid Cancer

External beam radiation therapy uses high-energy rays (or particles) to destroy cancer cells or slow their growth. A carefully focused beam of radiation is delivered from a machine outside the body.

This type of radiation therapy is most often used to treat medullary thyroid cancer and anaplastic thyroid cancer. For cancers that take up iodine (most differentiated thyroid cancers) radioiodine therapy is usually a better treatment.

External beam radiation therapy is often used for cancers that don't take up iodine and have spread beyond the thyroid. This might be done to help treat the cancer or to lower the chance of cancer coming back in the neck after surgery.

If a cancer does not respond to radioiodine therapy, external radiation therapy may be used to treat cancer that has come back in the neckor distant metastases that are causing pain or other symptoms.

External beam radiation therapy is usually given 5 days a week for several weeks. Before your treatments start, the medical team will take careful measurements to find the correct angles for aiming the radiation beams and the proper dose of radiation. The treatment itself is painless and much like getting a regular x-ray. Each treatment lasts only a few minutes, although the setup time — getting you into place for treatment — usually takes longer.

Possible side effects

The main drawback of this treatment is that the radiation can destroy nearby healthy tissue along with the cancer cells. Some patients get skin changes similar to a sunburn, but this slowly fades away. Trouble swallowing, dry mouth, hoarseness, and fatigue are also potential side effects of external beam radiation therapy aimed at or near the thyroid.

To reduce the risk of side effects, doctors carefully figure out the exact dose needed and aim the beam as accurately as they can to hit the target.

More information about radiation therapy

To learn more about how radiation is used to treat cancer, see Radiation Therapy.

To learn about some of the side effects listed here and how to manage them, see Managing Cancer-related Side Effects.

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.

American Thyroid Association Guidelines Task Force, Kloos RT, Eng C, Evans DB, et al. Medullary thyroid cancer: Management guidelines of the American Thyroid Association. Thyroid. 2015 25;19:567-610.

American Thyroid Association (ATA) Guidelines Taskforce on Thyroid Nodules and Differentiated Thyroid Cancer. Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer. Thyroid. 2016; 26:1-133.

Brierley JD. Differentiated thyroid cancer: External beam radiotherapy. https://www.uptodate.com/contents/differentiated-thyroid-cancer-external-beam-radiotherapy. UpToDate website. Updated April 27, 2018. Accessed February 19, 2019. 

Davidge-Pitts CJ and Thompson GB. Chapter 82: Thyroid Tumors. In: DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles and Practice of Oncology. 10th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2015.

National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Thyroid Carcinoma. V.3.2018. Accessed at https://www.nccn.org/professionals/physician_gls/pdf/thyroid.pdf on February 20, 2019.

Schneider DF, Mazeh H, Lubner SJ, Jaume JC, and Chen H. Chapter 71: Cancer of the Endocrine System. In: Niederhuber JE, Armitage JO, Dorshow JH, Kastan MB, Tepper JE, eds. Abeloff’s Clinical Oncology. 5th ed. Philadelphia, Pa. Elsevier: 2014.

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

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