After you've had surgery for thyroid cancer, you may have treatment with radioactive iodine (I-131). The thyroid gland absorbs nearly all the iodine in the blood. When a large dose of radioactive iodine is taken into the body, it can destroy the thyroid gland and thyroid cancer cells with minimal effect on the rest of the body. The goal of this treatment is to target and kill any remaining thyroid cells or thyroid cancer cells anywhere in your body. You take radioactive iodine as a capsule or liquid to treat the slow growing differentiated thyroid cancers, also called papillary and follicular thyroid cancer. It is not used to treat medullary or anaplastic thyroid cancer, as these cancer types do not take up iodine.
Radioactive iodine can destroy the thyroid in a growing fetus. Be sure to tell your doctor if you might be pregnant before you have this treatment. Your doctor may suggest you wait six months to a year after radioactive iodine therapy before you try to get pregnant. There has been evidence suggesting a greater risk of miscarriage as well as birth defects and aplastic anemia occurring in pregnancies within the first year after radioactive iodine therapy. One year following treatment also provides time to confirm remission of the cancer and for the thyroid hormone status to normalize. No significant adverse effects have been identified in children whose parents were treated with radioactive iodine in the past (conception occurring after the one year mark following treatment.)
Radioactive iodine therapy is most effective if you have high blood levels of thyroid stimulating hormone (TSH), which causes thyroid cells in the body, including thyroid cancer cells, to take up the iodine. After thyroid surgery, you may be given a drug called Thyrogen (thyrotropin) to raise your TSH levels before treatment. TSH levels can also be raised by not taking thyroid hormone after surgery for a few weeks, but this can cause bothersome side effects such as feeling tired and depressed. You may be instructed to follow a low iodine diet for a few weeks before treatment.
During radioactive iodine therapy for thyroid cancer, you take radioactive iodine as a pill or liquid. Any remaining thyroid cells ingest the iodine and the cells are destroyed. You may have thyroid scans after this type of radiation to show whether you have any more cancer.
You need to take a few precautions after this type of treatment. For instance, you must stay away from other people for a few days after taking radioactive iodine because your body will give off radiation for some time after the treatment. You may need to stay in the hospital during this time. Your doctor may also suggest that you drink a lot of fluids. Fluids will help flush the radioactive iodine out of your system. Your doctor also may suggest that you flush the toilet several times after urinating. This helps rid the toilet of radioactive material. Most radiation from I-131 is gone in about one week. Ask your doctor about other precautions you should take after treatment and how long you need to take them. You also need to know that high doses of I-131 kills normal thyroid cells, which make thyroid hormone. After radioactive iodine therapy, you will need to take thyroid hormone pills to replace the natural hormone that your body no longer can make on its own.
Radioactive iodine therapy does not usually cause immediate side effects. Some people may have neck pain, nausea, dry eyes, and dry mouth. Rarely, men may become infertile. Radioactive iodine may have an effect on women's ovaries. Irregular periods have been seen for up to one year following treatment. Many doctors recommend that women who have undergone radioactive iodine therapy should not get pregnant for six months to a year following treatment. This therapy may also carry a small risk of leukemia later in life. More research is needed to determine exactly how much the risk is increased.