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External 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.

When might external radiation be used for thyroid cancer?

This type of radiation therapy is most often used to treat medullary thyroid cancer or anaplastic thyroid cancer. These cancers don’t take up iodine.

For cancers that do take up iodine (most papillary and follicular thyroid cancers), is usually a better treatment option. However, if a papillary or follicular cancer isn’t helped by radioiodine therapy, external radiation therapy may be an option for treatment.

External radiation therapy is most often used for cancers that have spread outside of the thyroid. This might be done to help treat the cancer (or to treat symptoms such as pain), or to help lower the chance of cancer coming back in the neck after surgery.

How is external radiation given?

External radiation therapy to the neck area is usually given 5 days a week for several weeks.

Before your treatments start, the medical team will take careful measurements to find the proper dose of radiation and the correct angles for aiming the radiation beams.

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 of radiation therapy for thyroid cancer

The main drawback of this treatment is that the radiation can damage nearby healthy tissue along with the cancer cells. Possible side effects include:

• Skin changes (similar to a sunburn) in the area being treated
• Trouble swallowing
• Dry mouth
• Hoarseness
• Feeling very tired

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. This is often done with an advanced type of treatment known as intensity-modulated radiation therapy (IMRT).