Your thyroid gland absorbs nearly all of the iodine in your body. Because of this, radioactive iodine (RAI, also called I-131) can be used to treat thyroid cancer. The RAI collects mainly in thyroid cells, where the radiation can destroy the thyroid gland and any other thyroid cells (including cancer cells) that take up iodine, with little effect on the rest of your body. The radiation dose used here is much stronger than the one used in radioiodine scans, which are described in Tests for Thyroid Cancer.
This treatment can be used to ablate (destroy) any thyroid tissue not removed by surgery or to treat some types of thyroid cancer that have spread to lymph nodes and other parts of the body.
Treatment of thyrotoxicosis
Major uses of 131I include the treatment of thyrotoxicosis (hyperthyroidism) due to Graves’ disease, and sometimes hyperactive thyroid nodules
Treatment of thyroid cancer
Iodine-131, in higher doses than for thyrotoxicosis, is used for ablation of remnant thyroid tissue following a complete thyroidectomy to treat thyroid cancer.