Radioactive iodine (RAI) treatment involves swallowing a capsule or liquid form of radioactive iodine that thyroid cells take up (absorb), destroying them. It’s effective because healthy cells in the body don’t usually absorb the radioactive iodine.

Most people with thyroid cancer get just one or two doses of RAI therapy.

Thyroid cancer specialists at Memorial Sloan Kettering often recommend RAI after surgery in which we remove the thyroid (a thyroidectomy). This destroys abnormal thyroid tissue that might have been left behind or missed during surgery.

We may also recommend RAI treatment for thyroid cancer that either:

• comes back after being treated (recurs)
• has spread (metastasized) to other parts of the body

RAI Treatment for Different Types of Thyroid Cancer 

To be effective, your thyroid cancer must be the type that absorbs radioactive iodine.

Studies show that RAI therapy increases how long some people with the following types of thyroid cancer live:

• follicular thyroid cancer
• papillary thyroid cancer that has spread

RAI therapy sometimes helps control the disease in people with differentiated thyroid cancer that that appears likely to spread or has already spread.

How to Avoid Hypothyroidism during RAI Therapy

People getting RAI therapy should stop taking thyroid replacement medicine for a while. During this time, symptoms of underactive thyroid (hypothyroidism) can develop. Signs and symptoms of hypothyroidism include

• tiredness and fatigue
• sensitivity to cold
• weight gain caused by no apparent reason
• constipation

To help avoid these symptoms from developing, we usually recommend that you take a synthetic form of TSH (Thyrogen®) at the beginning of RAI therapy, and in repeated doses if necessary.