Radioactive Iodine Treatment

Radioactive iodine may be used as a treatment for certain thyroid disorders and thyroid cancer.

The thyroid gland needs iodine to produce thyroid hormones. The follicular cells of the thyroid have channels or pores to actively absorb iodine for making thyroid hormone. Radioactive iodine takes advantage of the fact that thyroid cells and thyroid cancer cells absorb iodine; therefore, it has been used to diagnose or treat various thyroid disorders.

Iodine is made into two radioactive isotopes — I-123 and I-131 — that are commonly used in patients with thyroid disease. A radioactive isotope (RAI) is a substance that gives off radiation. RAI is given by mouth, in pill or liquid form. RAI is then absorbed by the thyroid cells and can be used to diagnose or treat thyroid problems.

I-131 is commonly used to treat thyroid disorders, such as hyperthyroidism, through RAI ablation (medically destroying the thyroid gland without surgery). In addition, large doses of I-131 are used to destroy thyroid cancer cells, which are killed after absorbing the dose of radioactive iodine.

RAI after thyroid cancer surgery

No matter how expert the thyroid surgeon is, in most cases, a small amount of thyroid tissue remains after thyroidectomy (removal of thyroid gland). For patients with thyroid cancer, we use RAI to destroy the remaining thyroid cells after surgery — a treatment called remnant ablation.

The goal of RAI remnant ablation treatment is to kill any remaining thyroid cells. This is important for several reasons:

  1. We assume any remaining cells are cancerous and by killing them we hope to reduce the chances that the cancer will grow back (decrease the chance of recurrence).
  2. Thyroid cells make a protein called thyroglobulin (Tg). If we can destroy all of the thyroid cancer cells, the Tg should be undetectable.

While the majority of patients will receive RAI remnant ablation, we strive to give the lowest radiation dose possible. In some cases, where a child does not have any evidence of remaining disease, we can avoid RAI completely.

For patients who need RAI treatment, we only give additional doses of RAI after we determine the thyroid cancer is growing — as indicated by an increase in Tg levels — and if the remaining cancer cannot be surgically removed.

There are a number of different radiologic studies and nuclear medicine studies that can be used to find remaining thyroid cancer. These techniques will be discussed with you and your child if and/or when necessary.

Note: All female patients of child-bearing age must have a pregnancy test before they are given a treatment dose of RAI. RAI, whether I-123 or I-131, should never be used in a patient who is pregnant or nursing.

Before RAI treatment

Prior to receiving RAI for treatment of thyroid cancer, patients must be placed on a low-iodine diet and their TSH level must be increased.

Low-iodine diet

Patients are placed on a low-iodine diet two weeks prior to receiving radioactive iodine. This makes them iodine-deficient and increases the chance that the thyroid cells will absorb the radioactive iodine dose.

Increase the TSH level

A high thyroid-stimulating hormone (TSH) level increases the ability of thyroid cells to absorb iodine. TSH is secreted by an area of the brain called the pituitary gland, which tightly controls the amount of hormone produced by the thyroid gland.

Increasing the TSH level can be accomplished by stopping the thyroid hormone replacement for two to four weeks (thyroid hormone withdrawal; THw) or by giving a man-made form of TSH called recombinant human TSH (rhTSH) until the TSH reaches the desired level. Advantages and disadvantages of THw vs. rhTSH can be discussed with your provider.

Radioactive Iodine Precautions and Side Effects

There are both regulatory (by-law) and medical precautions to using radioactive iodine (RAI).

Regulatory precautions

The regulatory precautions are regulated by each state. They dictate if treatment can be performed in the outpatient setting or if the patient needs to be admitted to the Hospital and placed under radioactive precautions. Prior to leaving the Hospital, the nuclear medicine department and your thyroid treatment team will discuss the precautions and review ways to decrease the side effects and risks of exposure after receiving radioactive iodine.

Medical precautions

The medical precautions are for the caregiver and family as well as the patient. Since I-131 produces radiation, patients must do their best to avoid radiation exposure to others, particularly to pregnant women and small children.

Medical precautions will be given to you during the "pre-ablation" or "pre-RAI treatment" appointment. These precautions are very specific and should be followed as closely as possible to reduce potential exposure to others and to decrease the likelihood of short- and long-term medical complications associated with RAI.

Side effects of RAI treatment

All medical treatments have side effects; RAI is no different. In previous years, the goal of therapy was to get rid of all thyroid cancer cells no matter the total dose of RAI. With increased awareness of the potential risks associated with RAI, the current approach attempts to more carefully balance the risks and benefits of treatment.

RAI therapy is associated with short- and long-term medical risks, including:

  • Nausea within the first few hours of taking the dose (frequently managed with anti-nausea medication).
  • Inflammation of the salivary glands. Symptoms usually include decreased production of saliva leading to a dry mouth (called “xerostomia”) and subsequent decreased taste as well as an increased risk of developing dental cavities. Strict dental hygiene with brushing, dental floss and fluoride mouthwash may help decrease the risk of cavities.
  • Permanent salivary gland problems may occur in up to 15 percent of patients. The use of sour candy or lemon juice should be used beginning within 2 hours of receiving a treatment dose of radioactive iodin. Continue using with repeat candies every 15-30 minutes over the first 24hours. The goal is to stick is to stick to this schedule as much as possible, even over-night, using an alarm to wake up. After the first 24 hours, keep the same schedule during the day but can be decreased overnight to every 1-2 hours. After 48 hours, you can stop.
  • Decreased lung function in patients with a history of thyroid cancer that has metastasized to the lungs. This change may be due to the presence of the cancer or a side effect of the RAI treatment. Pulmonary function testing (PFT) should be followed for all patients with a history of papillary thyroid cancer (PTC) that has spread to the lungs.
  • Temporary or permanent decrease in blood cell counts.
  • Increased lifetime risk of developing second, non-thyroid cancers in patients exposed to RAI compared to those who were not, to include cancers of the blood system (leukemia), salivary gland, urinary system, gastrointestinal and others.
  • Special concerns for women: Temporary menstrual irregularities have been reported in up to 17 percent of females under the age of 40 years, 65 percent of whom were treated with a single dose of RAI. For patients interested in starting a family, there does not appear to be an increase in infertility or birth defects in pregnancies after RAI. However, it is recommended to avoid conception during the year after a large RAI dose to decrease the chances of a miscarriage.
  • Special concerns for men:  In boys who have completed puberty, there may be a temporary increase in one of the hormones that regulates the function of the testes (follicle stimulating hormone; FSH). For the majority, this is temporary and will be unnoticed except for the blood test abnormality. However, several doses of RAI may lead to decreased sperm counts and temporary infertility. Testosterone production is generally not affected. Males should avoid attempts at conception for at least four months after RAI treatment. Sperm banking may be recommended for patients who are expected to need several doses of RAI for thyroid cancer.

The Pediatric Thyroid Center at CHOP is committed to determining which patients will or will not benefit from RAI therapy. You, the patient and family, are important members of the treatment team. Be informed and be involved. Know the risks and the benefits of the treatment being recommended and the expertise of the center providing your care. The potential risks of complications decrease if you receive care in a center dedicated to the care of pediatric patients with thyroid disease.

Ongoing care and research at CHOP