99% of the types of radiation released by I-131 are beta rays, which have an effective range of 1-2mm in the tissue, and therefore do not damage the tissue around the thyroid gland. The irradiation to the surrounding population mainly comes from 1% of γ-rays, which is a low dose and does not require special protection for adult family members. Medical doses of I-131 generally do not cause cancer. We know that there are generally two kinds of radioactive effects, random effects and non-random effects. Random effects have nothing to do with dose, and are events that happen by chance. The thing that causes cancer is mainly related to the body’s DNA repair ability, in addition to the effect of radiation on chromosomes. In other words, if there is a problem with the DNA repair ability, even if it is not the radiation that causes chromosome damage, other things such as drinking, smoking and drugs may cause cancer to occur, so it is better not to take such random events to heart. Special attention needs to be paid to children. The high incidence of thyroid cancer in children in the region after Chernobyl suggests that children should still avoid I-131 treatment, and its application in children is currently restricted in clinical practice.