131 iodine: Medical use. Carcinogenetic and genetic effects.

131 radioiodine is used for treating patients with thyrotoxicosis and differentiated thyroid carcinoma. Its therapeutic effect is elated to the radiation dose delivered to the thyroid tissue. The radiation dose is related to its radio-active concentration (ratio between the radioactive uptake and the mass of functional tissue) and its effective half-life. Follow-up studies of patients exposed to I-131 did nor demonstrate any tumorigenic effect of I-131 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 I-131 ( > 15 GBq). No generic effect fins been found in the studies of the outcome of pregnancies in women exposed to I-131 for thyroid carcinoma. These data indicate that there is no scientific reason to avoid the use of I-131 even in young patients when therapeutic benefits can be obtained.