[131 iodine: medical use. Carcinogenic and genetic effects]

131 radioiodine is used for treating patients with thyrotoxicosis and differentiated thyroid carcinoma. Its therapeutic effect is related to the radiation dose delivered to the thyroid tissue. The radiation dose is related to its radioactive concentration (ratio between the radioactive uptake and the mass of functional tissue) and its effective half-life. Follow-up studies of patients exposed to 131I did not demonstrate any tumorigenic effect of 131I on the thyroid gland in adults, but do exclude such an effect in children. The dose delivered to other tissues is relatively low, and significant risk of cancer and leukemia has been found only in patients exposed to high cumulative activities of 131I (> 15 GBq). No genetic effect has been found in the studies of the outcome of pregnancies in women exposed to 131I for thyroid carcinoma. These data indicate that there is no scientific reason to avoid the use of 131I even in young patients when therapeutic benefits can be obtained.