NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,846 terms related to cancer and medicine.

Browse the dictionary by selecting a letter of the alphabet or by entering a cancer-related word or phrase in the search box.

radioactive iodine
(RAY-dee-oh-AK-tiv I-oh-dine)
A radioactive form of iodine, often used for imaging tests or to treat an overactive thyroid, thyroid cancer, and certain other cancers. For imaging tests, the patient takes a small dose of radioactive iodine that collects in thyroid cells and certain kinds of tumors and can be detected by a scanner. To treat thyroid cancer, the patient takes a large dose of radioactive iodine, which kills thyroid cells. Radioactive iodine is also used in internal radiation therapy for prostate cancer, intraocular (eye) melanoma, and carcinoid tumors. Radioactive iodine is given by mouth as a liquid or in capsules, by infusion, or sealed in seeds, which are placed in or near the tumor to kill cancer cells.