Iodide I-131

Iodide I-131 (as Sodium iodide I-131) is a radioisotopic drug used for the treatment and palliation of thyroid malignancy. Iodine-131 is notable for causing mutation and death in cells that it penetrates, which is due to its mode of beta decay. As a result of beta decay, approximately 10% of its energy and radiation dose is via gamma radiation, while the other 90% (beta radiation) causes tissue damage without contributing to any ability to see or image the isotope. Low levels of beta radiation are also known for causing cancer as this dose is highly mutagenic. For this reason, less toxic iodine isotopes such as I-123 are more frequently used in nuclear imaging, while I-131 is reserved for its tissue destroying effects. Because the thyroid gland naturally takes up iodine from the body, therapeutic methods using radioisotopes can take advantage of this mechanism for localization of drug to the site of malignancy. Therapeutic solutions of Sodium Iodide-131 are indicated for the treatment of hyperthyroidism and thyroid carcinomas that take up iodine. Palliative effects may be observed in patients with advanced thyroid malignancy if the metastatic lesions take up iodine. It is also indicated for use in performance of the radioactive iodide (RAI) uptake test to evaluate thyroid function.