The thyroid gland produces hormones that help to regulate heart rate, blood pressure, body weight and temperature. To produce thyroid hormones, the body needs iodine for normal cell metabolism, according to the National Institutes of Health. Surgery, hormone treatment, radioactive iodine, external radiation therapy and chemotherapy are used to treat thyroid cancer depending on the type and size of the tumor, according to the National Cancer Institute. The most common nuclear medicine treatment for thyroid cancer uses radioactive iodine.
What is Radioactive Iodine?
Most of the iodine used in the body is absorbed through the thyroid gland. When cancer develops in the thyroid gland, radiation treatments are often used to kill cancer cells. Treatments may be external, using a linear accelerator, or systemic, using pills, liquids or other methods of delivering radiation to the tumor. The most commonly used systemic agent is radioactive iodine, or I-131, according to the American Cancer Society. Radioactive iodine is an isotope treated to deliver radiation to cells that absorb iodine. When I-131 is given as a pill or liquid, the thyroid gland and any thyroid cancer cells in the gland or elsewhere in the body absorb the agent, killing both normal cells and cancerous cells.
When is Radioactive Iodine Used?
Radioactive iodine is most often used with papillary or follicular type thyroid cancers that have spread to lymph nodes or other areas in the body, according to the National Cancer Institute. When surgery to remove the thyroid gland is the initial treatment, I-131 may be administered to kill any cancer cells not removed. For radioactive iodine to be effective, high levels of thyroid stimulating hormones must be present in the patient's blood to encourage the cells to absorb the iodine. High dose radioactive iodine may also be used if the cancer returns. Diagnostic procedures done in the Nuclear Medicine Department using very low doses of radioactive iodine should not be confused with high-dose treatment that kills cells.
Are There Other Radioactive Agents?
Radioactive iodine is the standard of care in systemic radiation for thyroid cancer, but other agents are being developed and tested. Clinical trials are carefully structured research studies to determine if new treatment options are safe and effective. Clinical trials of radioactive agents in thyroid cancer other than I-131 are ongoing. The National Cancer Institute provides lists of available trials for thyroid cancer on its Web site, including a radioactive agent called high-dose 111In-Pentetreotide.
