Radiation Therapy for Thyroid Cancer

Your thyroid gland absorbs nearly all of the iodine in your blood as part of its normal functioning. Radioactive iodine can destroy cancer cells not removed by surgery and those that have spread beyond the thyroid. The cell takes up the iodine and the radiation in the iodine is released, delivering a lethal dose of radiation to the cancer cells. This treatment is especially useful if you have a papillary or follicular cancer that is larger than 1.5 centimeters or has spread to the neck or other parts of the body. But it is not indicated for small cancers that are only located in the thyroid gland. It is not used for medullary or anaplastic thyroid cancers because these tumors do not take up iodine.

• Radioactive iodine (radioiodine) - Radioiodine can destroy the rest of the thyroid gland and thyroid cancer (if the cancer takes up iodine) without affecting the rest of your body. Radioiodine is usually given as a capsule or in liquid form about 6 weeks after surgery. If you receive the usual dose, you will probably stay in the hospital for about 2 or 3 days while you are treated. If you receive a small dose, you will probably not have to stay in the hospital.

External beam radiation therapy uses high-energy x-rays or other types of radiation to kill cancer cells. It is not used for thyroid cancers that take up iodine and can therefore be more effectively treated with radioiodine therapy. However, it is sometimes used to treat cancers that do not take up iodine (and therefore cannot be treated with radioactive iodine) and have spread beyond the thyroid capsule to reduce the chance that the disease will come back (recur) in the neck. In addition, radiation treatment is usually used to treat anaplastic thyroid cancer.

• External beam radiation therapy (EBRT) - Radiation from a high-energy x-ray machine (linear accelerator) outside the body is focused on the cancer cells. Most people are treated with EBRT for a few minutes 5 days a week for a few weeks or months as an outpatient.