Harvard Women's Health Watch

By the way, doctor: How does radiation cause thyroid cancer?

Q. What kind of radiation causes thyroid cancer? What about microwave ovens and dental x-rays?

A. The thyroid is a butterfly-shaped gland located at the front of the neck beneath the larynx. Compared to many other organs, the thyroid gland is particularly sensitive to certain types of radiation. For example, radiation from x-ray and radiation therapy machines and radioactive atoms are linked to both benign and malignant thyroid tumors. The younger the age of exposure and the higher and more direct the dose, the more likely it is that a thyroid tumor will develop in adulthood.

With therapeutic radiation, the thyroid risk is greatest when the head and neck tissues are exposed directly to the radiation beam. With dental x-rays, which are diagnostic, the thyroid is usually protected with a lead apron (each dose is very small, but the effects can be cumulative). In the United States, radiation was used during the 1940s and '50s to treat conditions such as chronic cystic acne and fungal infections of the scalp in children and teenagers. Radiation-tipped rods were inserted through the nose to shrink tonsils and adenoids. People who received such treatments as children are at increased risk for thyroid cancer in adulthood and should have regular thyroid examinations. High radiation exposures to an adult carry less of a risk of thyroid cancer.

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