Radioactive Iodine (I-131) Therapy for Hyperthyroidism

13 May.,2024

 

Radioactive Iodine (I-131) Therapy for Hyperthyroidism

Radioactive Iodine (I-131) Therapy for Hyperthyroidism

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Radioiodine therapy is a nuclear medicine treatment. Doctors use it to treat an overactive thyroid, a condition called hyperthyroidism. They also may use it to treat thyroid cancer. When a small dose of radioactive iodine I-131 (an isotope of iodine that emits radiation) is swallowed, it is absorbed into the bloodstream. The isotope is concentrated by the thyroid gland, where it begins destroying the gland's cells.

Your doctor will instruct you on how to prepare, how to take any necessary radiation safety precautions, and when to stop taking anti-thyroid medications. Tell your doctor if there's a possibility you are pregnant or if you are breastfeeding. Discuss any recent illnesses, medical conditions, allergies, and medications you're taking. This procedure requires little to no special preparation. However, you should not eat or drink anything after midnight on the day of treatment.

What is Radioiodine (I -131) Therapy and how is it used?

Radioactive Iodine I-131 (also called Radioiodine I-131) therapy is a nuclear medicine treatment. Doctors use it to treat an overactive thyroid, a condition called hyperthyroidism. Hyperthyroidism can be caused by Graves' disease, in which the entire thyroid gland is overactive, or by nodules within the gland which are locally overactive in producing too much thyroid hormone.

Nuclear medicine uses small amounts of radioactive material called radiotracers. Doctors use nuclear medicine to diagnose, evaluate, and treat various diseases. These include cancer, heart disease, gastrointestinal, endocrine, or neurological disorders, and other conditions. Nuclear medicine exams pinpoint molecular activity. This gives them the potential to find disease in its earliest stages. They can also show whether you are responding to treatment.

The thyroid is a gland in the neck that produces two hormones. These hormones regulate all aspects of the body's metabolism, the chemical process of converting food into energy. When a thyroid gland is overactive, it produces too much of these hormones, accelerating the metabolism.

Radioactive iodine (I-131), an isotope of iodine that emits radiation, is used for medical purposes. When a small dose of I-131 is swallowed, it is absorbed into the bloodstream in the gastrointestinal (GI) tract. It is concentrated from the blood by the thyroid gland, where it begins destroying the gland's cells.

Doctors also use radioactive iodine I-131 to treat thyroid cancer.

Who will be involved in this procedure?

A radiologist who has specialized training in nuclear medicine and others, possibly including an endocrinologist, thyroid surgeon, and radiation safety officer, will be part of your treatment team.

What equipment is used?

There is no equipment used during radioactive iodine therapy.

Who operates the equipment?

There is no equipment used during radioactive iodine therapy, the patient simply swallows a prepared dose.

Is there any special preparation needed for the procedure?

You should not eat or drink after midnight on the day of the procedure. If you have been taking anti-thyroid medications, you must stop at least three days before the therapy is given. Frequently, your doctor will recommend stopping anti-thyroid medication for five to seven days before therapy.

You will be able to return home following radioactive iodine treatment. However, you should avoid prolonged, close contact with other people for several days, particularly pregnant women and small children. Most of the radioactive iodine that has not been absorbed leaves the body during the first two days following the treatment, primarily through the urine. Small amounts will also be excreted in saliva, sweat, tears, vaginal secretions, and feces.

If your work or daily activities involve prolonged contact with small children or pregnant women, you should wait several days after your treatment to resume these activities. Patients with infants at home should arrange for care to be provided by another person for the first several days after treatment. Your radiologist can be more specific for your given situation, but this is usually for two to five days.

Your treatment team will give you a list of other precautions to take following your treatment with I-131. The following guidelines comply with the Nuclear Regulatory Commission:

  • Use private toilet facilities, if possible, and flush twice after each use.
  • Bathe daily and wash hands frequently.
  • Drink a normal amount of fluids.
  • Use disposable eating utensils or wash your utensils separately from others.
  • Sleep alone and avoid prolonged intimate contact for three or four days. Brief periods of close contact, such as handshaking and hugging, are permitted.
  • Launder your linens, towels, and clothes daily at home, separately. No special cleaning of the washing machine is required between loads.
  • Do not prepare food for others that requires prolonged handling with bare hands.
  • If you are breastfeeding, you must stop several days before to ensure that milk production has also stopped.
  • You should avoid becoming pregnant from six months to one year after treatment.
  • You must be sure you are not pregnant before receiving I-131. Many facilities require a pregnancy test within 24 hours prior to giving I-131 in all women of child-bearing age who have not had a surgical procedure to prevent pregnancy.

Patients who need to travel immediately after radioactive iodine treatment are advised to carry a letter of explanation from their physician. Radiation detection devices used at airports and federal buildings may be sensitive to the radiation levels present in patients up to three months following treatment with I-131. Depending on the amount of radioactivity administered, your endocrinologist or radiation safety officer may recommend continued precautions for up to several weeks after treatment.

Doctors do not use radioiodine therapy in pregnant patients. Depending on the stage of pregnancy, I-131 given to the mother may damage the baby's thyroid gland. If you are pregnant, discuss this issue with your doctor. When given to a nursing mother, radioactive iodine can reach a baby through her breast milk. Most physicians feel that this procedure should not be used in women who are breastfeeding unless they are willing to stop breastfeeding. Also, you should avoid getting pregnant for at least six to 12 months after treatment.

Pre-menopausal women should fully discuss the use of I-131 with their doctor.

How is the procedure performed?

Hyperthyroidism treatment is almost always done on an outpatient basis because the dose required is relatively small.

The radioiodine I-131 is swallowed in a single capsule or liquid dose and is quickly absorbed into the bloodstream in the gastrointestinal (GI) tract. It is concentrated from the blood by the thyroid gland, where it begins destroying the gland's cells. Although the radioactivity remains in the thyroid for some time, it is greatly diminished within a few days. The effect of this treatment on the thyroid gland usually takes between one and three months to develop. Maximum benefit occurs three to six months after treatment. Usually, a single dose is successful in treating hyperthyroidism. However, rarely, a second treatment is necessary. A third treatment is very rarely necessary.

What will I feel during this procedure?

Patients may experience pain in the thyroid after therapy like a sore throat. Ask your doctor to recommend an over-the-counter pain reliever if this occurs.

Are there permanent side effects from radioactive iodine therapy?

It is highly likely that this procedure will destroy some or most of your thyroid gland. Since hormones produced by the thyroid are essential for metabolism, most patients will need to take thyroid pills for the rest of their life following the procedure. Thyroid pills are inexpensive, and patients will typically be prescribed one pill per day. There are essentially no other permanent side effects from the procedure. The risk of cancer from this therapy is very small.

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Radioactive iodine therapy: 9 things to know

Radioactive iodine therapy has been used in the treatment of thyroid cancer since the early 1940s. But how does it work? Which patients need it? And how has its use changed over the years?

To learn more about this highly effective and well-established tool, we spoke with Jeena Varghese, M.D., who specializes in endocrine tumors.

What is radioactive iodine therapy?

Radioactive iodine therapy is a radiopharmaceutical. It involves the use of radioactive isotopes — in this case, Iodine-131 (I-131) — to diagnose or treat disease.

How is radioactive iodine therapy used?

Currently, radioactive iodine therapy is only used to treat hyperthyroidism (overactive thyroid gland) and certain types of thyroid cancer. It’s also used to help determine the root causes of hyperthyroidism and to see if certain thyroid cancers have spread to other parts of the body.

How does radioactive iodine therapy work?

The thyroid cell’s job is to make hormones that govern various body processes, such as temperature regulation and metabolism. There are two different types: follicular and para-follicular. Follicular thyroid cells need iodine to do their job, so they take it from the foods we eat. And when someone has a thyroid disorder, we can often use that same mechanism to diagnose and treat it. So, in a sense, radioactive iodine therapy was the first true targeted therapy.

Before administering radioactive iodine therapy, we may have patients follow a low-iodine diet for a few days. This deprives the thyroid of iodine and makes it “hungry” for that element. Then, we give patients radioactive iodine molecules in the form of a pill. Since thyroid cells can’t tell the difference between radioactive and non-radioactive iodine, they absorb it quickly. Any radioactive iodine not absorbed by the thyroid is excreted by the body within a few days.

When used for diagnosis, very small amounts of radioactive iodine help highlight the areas where cancerous thyroid cells are on scans.

When we’re using radioactive iodine therapy to treat thyroid cancer or hyperthyroidism, higher doses are required. The iodine molecules emit radiation, which destroys the malfunctioning thyroid cells.

Can all thyroid cancers be treated using radioactive iodine therapy?

No. It’s only used for patients with certain types of differentiated thyroid carcinomas — specifically, papillary and follicular thyroid cancer. But not even all differentiated carcinomas have the ability to take up iodine. Undifferentiated or medullary thyroid carcinomas will not benefit from iodine therapy.

Can any other organs or cancers be treated with radioactive iodine therapy?

No. Very few cells in the body absorb iodine. So, the unique advantage to using this material is knowing that it will eventually end up in the thyroid gland.

What are common side effects of radioactive iodine therapy?

Any time you’re treated with radioactive material, there’s a certain amount of risk involved. In this case, the iodine targets the thyroid gland, but other glands, such as salivary glands, may also take up some radioiodine. So, patients may develop dry mouth or an altered sense of taste. The latter is actually quite common, but usually temporary.

Papillary thyroid cancer, in particular, is often seen in young women. Exposure to radiation could affect their fertility, so if they’re of child-bearing age, we usually counsel them to avoid conception for at least a year after treatment.

There’s also a risk of radiation exposure to the people around a patient treated with radioactive iodine therapy. So, we warn those patients to avoid pregnant women and children, stay a certain number of feet away from everyone else, and take other precautions, such as washing their own clothing, eating with separate utensils, and not sharing a bed or a bathroom with anyone else until their treatment is complete.

Usually, patients won’t have to isolate themselves for more than about five days. So, many opt to get treatment on a Friday or a long weekend, then go back to work the following week. But everyone who gets radioactive iodine therapy has to follow these guidelines, so if a patient is unable to do so for any reason — whether space constraints or some other issue — we’ll likely admit them to the hospital.

Can you have radioactive iodine therapy more than once, or is it like regular radiation therapy, where it’s considered fairly risky to irradiate the same area twice?

Historically, radioactive iodine therapy has been given to patients more than once, because for a long time, it was the only treatment available for thyroid cancer. We continue to offer more than one treatment in some patients, if the disease recurs or spreads to other parts of the body.

Radioactive iodine therapy is a systemic and targeted treatment. So, if papillary or follicular thyroid cancer has spread to any other part of the body, we can still use this therapy to find and destroy it. It doesn’t matter where those cancerous cells might be.

The risk of developing a secondary malignancy due to radioactive iodine therapy is usually very, very small, but we do keep that in mind before prescribing it. And we wouldn’t do it if we ever thought the risks outweighed the benefits.

How has radioactive iodine therapy evolved over time?

A decade ago, we gave radioactive iodine therapy to everybody — even someone with the smallest papillary carcinoma. But review of the data shows that not all patients need it. We may not need to treat all thyroid cancers, as most grow slowly and patients have excellent outcomes with surgery alone.

So now, we’re leaning more towards giving less radioactive iodine therapy and doing less aggressive surgeries. Particularly if there’s a very low risk of recurrence, we may recommend only a partial thyroidectomy — or removal of a part of someone’s thyroid gland — and not give them radioactive iodine therapy at all.

Are there any other radiopharmaceuticals being used right now in the diagnosis or treatment of other cancers?

Yes. A radiopharmaceutical called Lutathera (Lutetium-177) has been approved by the Food and Drug Administration (FDA) for the treatment of neuroendocrine tumors.

There’s also a drug called Azedra (ultratrace iobenguane-131) that my colleague Camilo Jimenez, M.D. was instrumental in getting approved by the FDA for the treatment of pheochromocytoma. Azedra is currently the only drug approved by the FDA to treat this rare type of adrenal cancer.

A drug called TheraSphere (Yttrium-90) is also being used to treat liver cancer. And a drug called 177Lu-PSMA-617 is being investigated for the treatment of metastatic prostate cancer. It was granted a breakthrough therapy designation by the FDA in June, and is now under priority review.

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