Radioactive iodine therapy, also known as radioiodine ablation, uses a radioactive form of iodine to destroy any remaining thyroid tissue or cancer cells after surgery. It is primarily used in cases of differentiated thyroid cancer (papillary and follicular) that have a high risk of recurrence or have spread to nearby lymph nodes or distant sites. The radioactive iodine is taken orally, and it selectively targets and kills thyroid cells.