The radiation distance of iodine 131 in the thyroid gland during radioactive iodine 131 treatment is about 2mm, so contact with patients after completing radioactive iodine 131 treatment does not usually lead to radiation exposure. However, since iodine 131 is contained in the sweat, saliva, urine and feces of patients who have just undergone radioactive iodine 131 treatment, it is important to keep them away from children and pregnant women for 72 hours after completing radioactive iodine 131 treatment, otherwise they may be affected. Radioactive iodine 131 treatment is one of the treatment modalities for hyperthyroidism. If patients are treated with radioactive iodine 131 for hyperthyroidism, most of them will gradually develop hypothyroidism with the progress of time.