External beam radiation therapy uses high-energy rays (or particles) to destroy cancer cells or slow their rate of 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 can be more effectively 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 capsule, 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 usually involves treatments 5 days a week for about 6 weeks. 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, hoarseness, and fatigue are also potential side effects of external beam radiation therapy.

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 about radiation therapy, see the American Cancer Society document, Understanding Radiation Therapy: A Guide for Patients and Families.

Last Medical Review: 04/28/2009
Last Revised: 05/14/2009