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Radioactive Iodine Therapy for Thyroid Nodules & Cancers
NYU Langone doctors may prescribe radioactive iodine therapy to manage some toxic, or overactive, nodules and some types of thyroid cancers.
They may prescribe it for people with a toxic nodule or a toxic multinodular goiter, which produce high levels of thyroxine and can lead to a condition called hyperthyroidism.
The therapy is especially beneficial for people with toxic nodules that do not respond to other medications or who need medication throughout their lifetime. Radioactive iodine therapy may also help shrink a large toxic multinodular goiter.
In this treatment, doctors give you a pill or liquid containing radioactive iodine. Iodine is a mineral found in table salt, seafood, and dairy products that the thyroid absorbs from the bloodstream and converts into thyroid hormone. Radioactive iodine travels to the thyroid, where it is absorbed and gradually destroys overactive thyroid tissue, along with other thyroid tissue.
Radioactive iodine may also be helpful for people with certain types of thyroid cancer. Papillary and follicular thyroid cancers develop from follicular cells, which absorb iodine. When you are given radioactive iodine, it is taken up by cancer cells and destroys them—including those that have spread to the lymph nodes or other parts of the body.
If you’ve had surgery for papillary or follicular thyroid cancer, your doctor may prescribe radioactive iodine afterward. It may help prevent the cancer from returning.
Radioactive iodine therapy is usually not effective for medullary and anaplastic thyroid cancers, because they do not absorb iodine.
Whether you’ve been treated for a toxic nodule or thyroid cancer, you may need to take the synthetic thyroid hormone levothyroxine daily as part of your long-term care because radioactive iodine therapy destroys healthy thyroid tissue.
NYU Langone doctors do not prescribe this therapy for everyone with papillary and follicular thyroid cancer. Those with small or less aggressive thyroid cancers may not benefit from treatment with radioactive iodine. Instead, a doctor may prescribe it for people whose cancer has spread or those who are at risk of a recurrence.
Risks include damage to the salivary glands, which may cause dry mouth and make swallowing difficult. It can also damage the tear ducts, causing dry eye. These side effects can be temporary or permanent. Our doctors can prescribe medications or recommend over-the-counter products or lifestyle changes to help manage them.
There is also a slight risk of developing a secondary cancer, such as breast, gastrointestinal, or blood cancer. This is why doctors carefully weigh the decision to prescribe radioactive iodine.
Radioactive iodine is not given to women who are pregnant or nursing a child. Generally, women who have received radioactive iodine should not get pregnant for about a year after the treatment. You and your doctor can discuss the risks involved and any precautions you need to take.
In men, radioactive iodine therapy may damage sperm temporarily. Healthy production of sperm returns after treatment.
Managing the Dose
When doctors use radioactive iodine therapy, they carefully manage the dose to make sure it targets the toxic nodule or cancer, minimizing the risk of side effects.
Your doctor ensures the dose avoids damage to the bone marrow, the blood-cell-producing tissue in bones. This reduces the risk of problems such as anemia—a low level of red blood cells. Our endocrinologists and nuclear medicine physicians can discuss dosing with you.
Although people usually return home after radioactive iodine therapy, doctors recommend precautions to minimize radiation exposure to others. If you are receiving a high dose, you may stay in a private hospital room for a few days so that other people are not exposed to the radioactivity.
Maximizing the Effectiveness of Radioactive Iodine Therapy
Radioactive iodine therapy for thyroid cancer is most effective in people who have high levels of thyroid-stimulating hormone, or TSH. This hormone is produced by the pituitary gland, which is located at the base of the brain and produces many hormones. TSH “tells” the thyroid to absorb iodine, which is then converted to thyroxine. The thyroid’s ability to absorb iodine is important for the success of radioactive iodine therapy.
If you’ve had surgery to remove part or all of the thyroid, your doctor may wait a few weeks before prescribing a replacement thyroid hormone. During that time, you experience what’s known as thyroid hormone withdrawal, which makes the pituitary excrete more TSH. Excess thyroid-stimulating hormone is necessary for the success of radioactive iodine therapy.
Another way your doctor may try to increase the effectiveness of radioactive iodine therapy is to give you an injection of a medication called recombinant human thyroid hormone—thyroid-stimulating hormone made in a laboratory. This injection is given for two days before radioactive iodine therapy begins. The medication elevates thyroid-stimulating hormone levels enough to make the radioactive iodine therapy as effective as thyroid hormone withdrawal.
Doctors may ask you to go on a low-iodine diet before treating you with radioactive iodine. This depletes the body’s levels of inorganic iodine, a mineral the thyroid uses to make thyroid hormone. When iodine levels are low, thyroid-stimulating hormone signals the thyroid cells to increase thyroid hormone production.
When radioactive iodine therapy is being considered for thyroid cancer, the body must be depleted of inorganic iodine, so the levels of thyroid-stimulating hormone increase, helping with the effectiveness of radioactive iodine therapy.
Our endocrinologists and nuclear medicine specialists offer advice on how to follow a low-iodine diet and avoid sources of excess iodine, such as certain vitamins and medications.
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