131I-Sodium Iodide is the standard diagnostic and therapeutic agent for diseases affecting the thyroid, including carcinomas. The dose depends on the application, but different forms are available, with the most common being swallowable gelatin capsules. 131I-Sodium Iodide was the first radiotherapeutic used in man and the first injection goes back to 1941. It became standard therapy as early as the beginning of the 1950s.
For diagnostic purposes, 131I-sodium iodide is used for localizing metastases associated with thyroid malignancies and for diagnosis of thyroid malfunction (hyperthyroidism, hypothyroidism). Doses are in the range 0.3–2 mCi.
At higher doses 131I-sodium Iodide is used for the treatment of carcinoma of the thyroid, including treatment of metastases, but also for the treatment of nodular goiter, hyperthyroidism (Graves-Basedov disease) and Plummer’s disease. Doses can go up to 150 mCi.