Risks of Radioiodine Treatment

"What are the special risks of radioiodine treatment for men? How long does a man have to wait before it is safe for him to father a baby, after RAI treatment?"

Concerns about potential genetic damage from therapeutic radioiodine persist. However, all studies that have looked for adverse effects on the offspring of treated patients have failed to demonstrate any problems. Nonetheless, physicians have suggested a number of "common sense" precautions.

The exposure to the gonads (ovaries or testicles) from a typical dose of radioiodine used to treat hypothyroidism is very similar to that from a number of other common radiologic procedures, for example, a barium enema, intravenous pyelography (kidney x-ray), or pelvic CT scan. In the case of treatment of the thyroid, most of the exposure is from radioiodine in the urine. This can be reduced by drinking plenty of fluids and trying to maintain an empty bladder for the first few days after treatment.

In men: the process of making sperm takes about 90 days. Spermatogenesis (the process of making new sperm) occurs in the testicle, then the sperm are stored in the epididymis (the duct from the testicle to the vas deferens) to allow them to mature prior to release at the time of ejaculation. Therefore, if a man waits for three to four months after radioiodine therapy, none of the sperm in his ejaculate would have been present at the time of the radioiodine exposure.

In women: all eggs are already formed and present in the ovary at the time of radioiodine treatment. Each month, one or more eggs are chosen to mature, and during the process of ovulation the chosen egg(s) are transported into the uterus. Since all the dormant eggs are exposed to the radioiodine at the time of treatment, there is no logical basis for a recommendation regarding the interval during which a woman should avoid conception. Certainly, she should avoid conception during the menstrual cycle occurring at the time of the radioiodine treatment. Prior recommendations suggesting that women wait for a year following treatment have recently been considered excessive by most experts, and intervals of three to six months are now generally recommended.

Any radiation exposure is potentially hazardous, and scientists have attempted to estimate the theoretical risk of radioiodine causing a genetic abnormality. Such estimates are about 3 in 100,000. This theoretical risk is considerably less than the spontaneous rate of genetic abnormalities, and therefore is not measurable in clinical studies.

Unfortunately, approximately 4.5% of babies are born with some abnormality. In controlled clinical studies, the incidence of birth defects in babies born to mothers who have taken radioiodine was identical to the incidence found in mothers who had not taken radioiodine. We therefore feel that radioiodine therapy is safe in women of child-bearing age.