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. Generally, this type of radiation treatment is not used for cancers that take up iodine (that is, most differentiated thyroid cancers), which are better treated with radioiodine therapy. It is more often used as part of the treatment for medullary thyroid cancer and anaplastic thyroid cancer.

When a cancer that does not take up iodine has spread beyond the thyroid, external radiation treatment may help treat the cancer or reduce the chance of the disease coming back in the neck after surgery. If a cancer does not respond to radioiodine therapy, external radiation therapy may be used to treat local neck recurrence or 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.

For more information see the Radiation Therapy section of our website,

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.

Last Medical Review: March 31, 2016 Last Revised: April 15, 2016

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