Radioactive Iodine Therapy

Iodine is a mineral found in foods such as fish, dairy products, and iodized salt. Your body needs iodine to produce thyroid hormones, which are essential for metabolism and many other body functions. Radioactive iodine therapy takes advantage of this natural need of thyroid cells for iodine to eliminate any abnormal thyroid cells, such as overactive thyroid cells, and to treat Graves’ disease or residual thyroid cancer cells that may remain after surgery for thyroid cancer (thyroidectomy).

Radioactive iodine (also called radioiodine or I-131) is a form of iodine that emits radiation. When administered, radioactive iodine is taken up by thyroid cells and destroys them. Radioactive iodine can destroy thyroid cells even if they are located in areas that cannot be treated by surgery, such as thyroid cancer cells that have spread to the lungs or other sites.

In children with high-risk forms of thyroid cancer, radioactive iodine therapy can improve outcomes and reduce the risk of thyroid cancer recurrence. However, radioactive iodine can only treat papillary or follicular types of thyroid cancer, not medullary thyroid cancer.

When used to treat Graves’ disease, radioactive iodine can destroy the overactive thyroid so that anti-thyroid medications (like methimazole) are no longer needed. Once the thyroid is destroyed, another daily medication (levothyroxine) will be needed permanently to restore normal thyroid levels. However, levothyroxine is easier to take, has fewer side effects, and requires less frequent blood tests than methimazole.

In general, radioactive iodine therapy may be appropriate for children whose thyroid cancer cannot be treated entirely with surgery (for example, if it has spread to other sites, like the lungs) or whose thyroid cancer has a high risk of recurring in the future. For children with less aggressive thyroid cancers with a low risk of recurrence, radioiodine therapy is usually unnecessary.

For any child with thyroid cancer, deciding whether to use radioactive iodine therapy involves considering the specific details of that child’s cancer and a careful discussion of the potential benefits and risks of therapy. An expert in pediatric thyroid cancer care will discuss with you all of these details and whether radioactive iodine therapy is recommended for your child.

When used to treat thyroid cancer, radioactive iodine can have some side effects. Short-term side effects last up to a few days and can include:

• Nausea
• Vomiting
• Swelling or pain in the area of the thyroid
• Swelling or pain of the salivary glands
• Dry mouth
• Changes in sense of taste

Females may have irregular or absent menstrual periods for one to three months following treatment, but radioactive iodine does not cause infertility or any birth defects in future children.

Long-term side effects are rare but can include:

• Dry mouth
• Changes in taste
• Dental cavities

Radioactive iodine therapy is also associated with a slightly increased risk of developing another cancer later in life. Although overall, these risks are low, they are important to consider and discuss with an expert physician when deciding whether the benefits of radioactive iodine therapy outweigh the risks for each child with thyroid cancer.

When radioactive iodine is used to treat Graves’ disease, the risk of side effects is very low because much smaller doses of radiation are used. A few patients may have transient swelling or pain of the thyroid gland. Also, radioactive iodine therapy can worsen eye problems in individuals with Graves’ eye disease, so this therapy requires special precautions in these patients.

When radioactive iodine therapy is given for thyroid cancer, proper preparation is important to ensure that the therapy has the best possible effect. This preparation involves two parts that increase the ability of thyroid cells to absorb radioactive iodine.

First, your child must have high levels of thyroid-stimulating hormone (TSH>25 uIU/mL) in their blood for radioactive iodine therapy to be effective. High levels of TSH stimulate thyroid cells to absorb iodine. If your child takes thyroid hormone replacement medication (levothyroxine), they will need to stop it about two weeks before radioactive iodine therapy begins to allow the TSH level to rise. After two weeks without levothyroxine, some children may have mild fatigue or constipation, but most children have minimal symptoms or no symptoms at all.

Second, your child will need to follow a low-iodine diet beginning one week in advance to make the therapy more effective. This means avoiding foods that contain iodine, including iodized salt, seafood, and products made with marine-based substances (such as carrageenan and alginate), most dairy products, processed meats, and red dye #3. Your child’s clinician will give you specific details about following a low-iodine diet, and a registered dietitian (nutritionist) can assist with planning for the diet.

When radioactive iodine therapy is given for Graves’ disease (hyperthyroidism), no special preparation is needed.

A nuclear medicine physician will administer radioactive iodine in a single dose, either as a pill or a liquid taken by mouth. In most cases, children can go home right after receiving radioactive iodine therapy, but in certain circumstances, they may need to be admitted to the hospital for a few days after treatment.

Because this treatment involves radiation, you and your child will need to take some safety precautions for a few days after radioactive iodine therapy to avoid exposing others to radiation (more information is below). Most of the radioactive iodine will be eliminated from your child’s body within two to three days after treatment, mostly in their urine but also in small amounts through saliva, sweat, and feces. After this time, the only radioactive iodine left in your child’s body will be a minimal amount in the targeted thyroid cells. This radioactive iodine will work to destroy these thyroid cells over the following weeks to months.

After your child received radioactive iodine therapy, other people can be exposed to radiation either by being physically close to your child or by being exposed to their body fluids (like saliva or urine). For this reason, your family should follow radiation safety instructions to limit their exposure. Some of the basics are outlined below, but your care team will explain all the details in advance and help you plan for these precautions after your child’s treatment.

• For the first two to three days after treatment, try to limit the time your child spends in close contact with others (within six feet), especially young children or pregnant women. Your child should not be in public places and should plan to stay home for these few days.
• Your child should be extra neat and tidy in the bathroom, flush the toilet twice, and wash their hands well.
• Do not share food, utensils, drinking straws, or towels.
• Your child will be able to return to school beginning five days after the therapy.

Founded in 2001, the Thyroid Center at Boston Children’s Hospital is the oldest program of its kind in the country and one of the only centers in the U.S. devoted exclusively to the care of children with thyroid diseases. The specialists in this multidisciplinary program have expertise in pediatric endocrinology, thyroid ultrasound, fine needle aspiration, thyroid surgery, nuclear medicine imaging, and radioactive iodine therapy.