What Is Radioactive Iodine (I-131) Used For?

The thyroid naturally takes up iodine to make thyroid hormones. I-131 follows this pathway and releases radiation near thyroid cells. After thyroid cancer surgery, it may be used to destroy remaining thyroid tissue or treat thyroid cells elsewhere in the body when the clinical team considers it appropriate.

The treatment is swallowed as a capsule or liquid. The amount of radiation around you decreases as the material leaves the body, mainly through urine. Your team will give individual instructions for limiting close contact and handling body fluids.

Tell the nuclear medicine team if you are pregnant, breastfeeding, taking thyroid medicine, or have recently received iodine-containing medicines or contrast. Follow instructions about food, medicines, hydration, bathroom hygiene, and contact with children or pregnant people.

Arrange your home routine before treatment, including sleeping arrangements and help with childcare if needed. Do not stop prescribed medicine or ignore isolation instructions unless your treatment team tells you to change them.

Contact your treatment team for persistent vomiting, inability to drink, severe neck swelling, marked neck pain, or symptoms that make the safety instructions difficult to follow. Seek emergency help for severe breathing or swallowing difficulty, facial swelling, confusion, or collapse.

Ask what the treatment is intended to target, how to prepare your thyroid medicine and diet, how long contact precautions are needed, and how follow-up thyroid tests or scans will be arranged. Ask when pregnancy or breastfeeding can safely be reconsidered.