Which isotope would be used in a pharmaceutical or drug to treat the thyroid with radiation therapy?

Radioactive Iodine, I-131 is for the treatment of thyroid diseases such as cancer and hyperthyroidism. When this is taken to the body in a form of liquid or capsule form, it is absorbed to the bloodstream, then goes to the thyroid gland and there it is concentrated and it works by destroying thyroid gland cells and it cannot affect other cells that can be destroyed by radiation.