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Radioiodine Therapy

What is radioiodine therapy?

If you have an overactive thyroid gland or have been diagnosed with thyroid cancer, your endocrinologist may prescribe radioactive iodine (radioiodine) as part of your overall treatment. You, your family, and your coworkers may have some questions about this therapy.


The thyroid gland produces hormones that regulate the body’s metabolism. In order to produce these hormones, the thyroid gland requires large amounts of iodine, which is found in seafood, table salt, bread, and various other foods. Iodine is an essential ingredient in the creation of thyroid hormone. Each molecule of thyroid hormone contains either three (T3) or four (T4) molecules of iodine. Most overactive thyroid glands are quite hungry for iodine. This led to the discovery in the 1940s that an overactive thyroid gland could be “tricked” into destroying itself by simply feeding it radioactive iodine. Your endocrinologist can also use radioiodine to treat some types of thyroid cancer.
Radioiodine has been used for more than 60 years in the treatment of thyroid diseases with remarkably few undesirable effects. However, problems may rarely occur when very large doses are given, including decrease in taste sensation and irritation of the salivary glands, or the gastrointestinal tract. No significant increase has been seen in the number of birth defects in children born later to women who have received this type of treatment. A very small number of patients may develop a second cancer years after treatment with a high dose of radioiodine.

Hyperthyroidism (overactive thyroid)

Before the development of current treatment options, the death rate from severe hyperthyroidism was as high as 50 percent. Now several effective treatments (antithyroid drugs, surgery, and radioiodine) are available, and death from hyperthyroidism is rare. Deciding which treatment is best depends on what caused the hyperthyroidism, its severity, and other conditions present. Endocrinologists are experienced in the management of thyroid diseases and can confidently diagnose the cause of hyperthyroidism and prescribe and manage the best treatment program for each patient.

Thousands of patients have received radioiodine treatment, including former President of the United States George Bush and his wife, Barbara. The treatment appears to be a very safe, simple, and reliably effective one. Because of this, it is considered by most thyroid specialists in the United States to be the treatment of choice for hyperthyroidism cases caused by overproduction of thyroid hormones.

Radioactive iodine is given by mouth, usually in capsule form, and is quickly absorbed from the bowel. It then enters the thyroid cells from the bloodstream and gradually destroys them. Although the radioactivity from this treatment remains in the thyroid for some time, it is largely eliminated from the rest of the body within a few days. Its effect on the thyroid gland usually takes between one and three months to develop, and maximal benefit is usually noted within three to six months.

It is not possible to eliminate “just the right amount” of the diseased thyroid gland, since radioiodine eventually damages all thyroid cells. Therefore, most endocrinologists usually strive to completely destroy the diseased thyroid gland with a single dose of radioiodine. This results in the intentional development of an underactive thyroid state (hypothyroidism), which is easily, predictably and inexpensively corrected by lifelong daily use of oral thyroid hormone replacement therapy. Although every effort is made to calculate the correct dose of radioiodine for each patient, not every treatment will successfully correct the hyperthyroidism, particularly if the goiter is quite large, in which case a second dose of radioactive iodine will be needed.

Thyroid cancer

The two most common types of thyroid cancer (papillary and follicular) can usually be treated with radioiodine because the cells are able to take up some iodine. Radioiodine is usually administered either:


An experienced thyroid surgeon can remove most of the thyroid with a very low risk of surgical complications. In many cases, surgery followed by thyroid hormone therapy is sufficient to treat
thyroid cancer. When it may not be sufficient, radioiodine can be used to destroy the remainder of the gland, which might harbor additional microscopic clusters of thyroid cancer. In that case, you may be advised not to use thyroid hormone replacement for several weeks after the operation, in order to allow the thyroid levels to drop below normal. This will lead to maximal stimulation of the remaining thyroid cells to concentrate iodine and be destroyed when you receive a dose of radioiodine. This treatment significantly reduces the possibility of recurrent cancer and also improves the ability to detect and treat any future cancer recurrences
that might develop.


Patients with residual thyroid cancer or cancer that has spread to regions outside of the neck can undergo a scan with a test amount of radioiodine. Scanning with radioiodine helps to determine the extent of “persistent” or “recurrent” thyroid cancer, whether it may respond
to additional doses of radioactive iodine, and how much radioactive iodine to use for treatment. If any iodine is concentrated in the areas of the thyroid cancer, another dose of radioiodine can be given to try to destroy the tumor. This treatment is safe, well tolerated, and
has successfully treated many cases of thyroid cancer even after the tumor has spread.

All patients with thyroid cancer should have regular follow-up examinations by an endocrinologist. Additional doses of radioactive iodine may be recommended if thyroid cancer remains (which is called “persistent”) or reappears later (which is called “recurrent”). Your thyroid hormone replacement therapy will need to be stopped long enough to allow you to become hypothyroid, so that maximum response to the treatment will occur.

What happens to the radioiodine after a treatment?

Since surgery removes the vast majority of thyroid tissue, much of the radioiodine will not be absorbed and will leave the body primarily through the urine. Small amounts will also be excreted in saliva, sweat, tears, vaginal secretions, and feces. Nearly all the radioactive
iodine will leave the body during the first two days after the dose has been given.

What about pregnancy?

If radioiodine is inadvertently administered to a woman who is subsequently discovered to be pregnant, the advisability of terminating the pregnancy should be discussed with the patient’s obstetrician and endocrinologist. Therefore, prior to administering diagnostic or therapeutic radioiodine treatment, pregnancy testing is mandatory whenever pregnancy is possible.

What about breast-feeding?

Small amounts of radioactive iodine are excreted in breast milk. Since radioiodine could permanently damage the infant’s thyroid, breastfeeding is not allowed.

Are future pregnancies possible?

As a precaution, males are advised to avoid fathering a child for several months. Females are advised to postpone pregnancy for six months or more in order to help stabilize their thyroid status for conception. Even though the amount of radioactivity retained may be small and there is no medical proof of an actual risk from radioiodine treatment, there is a theoretical risk to a developing fetus. Such precautions essentially eliminate direct fetal exposure to radioactivity,
and markedly reduce the possibility of conception with sperm that might theoretically have been damaged by exposure to radioiodine. You may need to contact your physician for guidance about methods of contraception.

Regulations regarding the use of radioiodine therapy are made by the U.S. Nuclear Regulatory Commission (NRC). Physicians and hospitals that administer this therapy must have a license to administer radioiodine, and must adhere to stringent regulations regarding its use. If you have any questions before or after receiving your treatment, please do not hesitate to contact your physician or your hospital radiation safety officer for clarification.

Is hospitalization necessary for treatment with radioiodine?

Treatment for hyperthyroidism is almost always done on an outpatient basis, because the dose required is relatively small in comparison with the doses typically used for treatment of thyroid cancer. If you have to take a larger dose of radioiodine for treatment of thyroid cancer, you may need to be admitted to the hospital for several days depending on the amount of radioiodine administered, your living environment, state of residence, or local practice patterns. If you require hospitalization, your hospital room will have frequently handled items (such as the television control, table, phone, faucet handles, etc.), covered with protective material, and the floor will be partially covered. These precautions are designed to prevent the radioactive iodine from contaminating those items that will be reused by other patients after your dismissal from the hospital. To limit the contamination of your personal items, you should bring a minimal
amount of belongings for your stay. Clothing should be limited to what you wear when you are admitted. You should use hospital gowns during your stay. You may want to bring disposable items like magazines and newspapers, but important or durable items like hardback books, work papers, and craft items should be left at home. All items will be monitored when you are discharged from the hospital. Check with your endocrinologist about any other issues.

Recommendations for reduction of exposure to others for several days after treatment:
• Use private toilet facilities, if possible; flush twice after each use.
• Bathe daily and wash hands frequently.
• Drink normal amount of fluids.
• Use disposable eating utensils or wash your utensils separately from others.
• Sleep alone and avoid prolonged intimate contact.
• Launder your linens, towels, and clothes daily at home, separately from others. No special cleaning of the washing machine is required between loads. This is because the radioiodine administered is water soluble.
• Do not prepare food for others that requires prolonged handling with bare hands (such as mixing a meat loaf or kneading bread).

Brief periods of close contact, such as handshaking and hugging, are permitted.

Your endocrinologist or radiation safety officer may recommend continued precautions for up to several weeks after treatment, depending on the amount of radioactivity administered. Patients receiving radioactive iodine should also carry information about their treatment
with them in order to fully inform authorities who are in charge of screening for radioactive materials in public areas such as airports and subways.

After treatment, should contact with other people be limited?

The amount of radioactive exposure to other persons during your daily activities will depend on the duration of contact and the distance you are from them. As an example, a person two feet away receives only one fourth the exposure of someone one foot away. Therefore, the general principle is to avoid prolonged, close contact with other people for several days.

If your work or daily activities involve prolonged contact with small children or pregnant women, you have to wait for several days after your treatment to resume these activities. Those patients with infants at home should arrange for care to be provided by another person for the first several days after treatment. It will not be necessary for you personally to stay elsewhere after your treatment, although you will need to sleep alone for several days.

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