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Radioactive Iodine for Thyroid Cancer

Treatment for Papillary and Follicular Thyroid Cancers

Radioactive iodine therapy is used after a thyroidectomy to treat 2 types of thyroid cancer: papillary thyroid cancer and follicular thyroid cancer. Radioactive iodine is also called radioiodine remnant ablation, and you may hear your doctor refer to it by that name.

Read about other treatments for thyroid cancer in our Patients' Guide to Thyroid Cancer.

In a thyroidectomy—a type of thyroid surgery used for thyroid cancer—the thyroid gland is removed. However, some thyroid cells may remain after the surgeon has finished—a remnant of thyroid cells that may have cancer. To prevent thyroid cancer recurrence, radioiodine remnant ablation (radioactive iodine therapy) is done to kill any remaining thyroid cells.

Thyroid cancer cells can also spread to other parts of the body, and if this has occurred, radioactive iodine can eliminate those cells as well.

How Radioactive Iodine Therapy Works

Thyroid hormone-producing cells are the only cells in your body that absorb iodine. They collect and concentrate iodine from our diets (such as from iodized salt) and use the iodine to make thyroid hormones (T3 and T4—read more about thyroid hormones in our thyroid gland overview).

Since no other cells in the body can absorb iodine, doctors can give radioactive iodine to destroy any thyroid cells while all other cells in the body are not affected. The majority of radioactive iodine, therefore, will be absorbed by remaining thyroid cells, regardless of if they have cancer.

Very small amounts of radioactive iodine may be absorbed by your salivary glands and the lining of your stomach, but it won't cause harm.

A certain form of radioactive iodine is used: I-131. That is the form that has been found to be the most effective in eliminating remaining thyroid cells.

Radioactive Iodine Therapy Basics

Your doctor will walk you through step-by-step what will happen in your radioactive iodine therapy. Here are some basics to keep in mind, though:

  • Radioactive iodine therapy is usually done 6 to 8 weeks after thyroid surgery. The swelling that occurs after surgery can affect how well blood flows to that part of your neck, and a free flow of blood is necessary to get as much radioactive iodine as possible to any remaining thyroid cells. Using radioactive iodine therapy 6 to 8 weeks after surgery leaves plenty of time for the swelling to go down.
  • You may need to go on a low-iodine diet for several weeks leading up to radioactive iodine therapy. This reduces how much iodine is in your body so that when you take the radioactive iodine, it's more easily absorbed by any remaining thyroid cancer cells. The Thyroid Cancer Survivors' Association has an excellent low-iodine cookbook you may want to consult. 
  • To help your remaining thyroid cells work harder and absorb more radioactive iodine when it's given, you may need to become hypothyroid for several weeks. Again, this is something your doctor will very carefully explain to you so that you understand why this is necessary and how it will be done. In short, becoming hypothyroid should cause your body to make more thyroid-stimulating hormone (TSH). More TSH in your body should make any remaining thyroid cells absorb more radioactive iodine.
  • An alternative to withholding thyroid replacement medication (eg, levothyroxine) is Thyrogen®. Thyrogen allows you to keep taking your thyroid hormone replacement medication before, during and after radioactive iodine therapy. Therefore, you avoid becoming hypothyroid.

  • Your exact dose will be determined by your doctor. You take radioactive iodine in a pill.

  • This is an outpatient procedure, but there are special requirements for when you return home. In years past, patients undergoing radioactive iodine had to be kept in the hospital for a few days. Now most patients are given the pill and sent home. However, you will be told to keep a distance from other people in our house for a few days until the radioactive substance wears off. This is something else your doctor will thoroughly explain.

Radioactive iodine therapy (radioiodine remnant ablation) has been used since the 1950s. The risk is extremely low, and the potential benefits are quite high. Radioactive iodine therapy is a very common and accepted treatment for thyroid cancer patients following thyroid surgery.