Sawka AM et al. (2007) A systematic review of the gonadal effects of therapeutic radioactive iodine in male thyroid cancer survivors. Clin Endocrinol (Oxf) [doi:10.1111/j.1365-2265.2007.03081.x]

Adjuvant radioactive iodine therapy is widely used to treat well-differentiated thyroid carcinoma (WDTC), but is known to result in radiation absorption by the testes, the long-term effects of which are unknown. To determine the effects of radioactive iodine on testis function and fertility in men with WDTC, Sawka et al. conducted a systematic review of controlled studies of radioiodine therapy in such patients.

Longitudinal studies of the effect of a single dose of ≤150 mCi (5.56 GBq) of radioiodine showed that serum levels of luteinizing hormone and follicle-stimulating hormone (FSH) peaked 2–6 months after radioiodine administration, and normalized in the majority of patients by 12–18 months. However, repeated or high cumulative radioiodine activities were associated with a greater risk of abnormalities. In one study, the majority of men who received >594 mCi (22 GBq) radioiodine had elevated FSH at 18 months. One 12-month study found a persistent reduction in sperm count in 7 of 53 patients; the cumulative dose of radioiodine correlated positively with FSH level, and inversely with sperm count. Another study with a mean follow-up >7 years found a positive correlation between radioiodine dose and FSH level. Radioiodine treatment was not found to affect rates of infertility, pregnancy loss or congenital malformation; however, sample sizes in these studies were small and the outcomes self-reported.

The authors recommend that sperm banking be offered to men if multiple doses of radioiodine are planned (particularly if single doses exceed 150 mCi), if the cumulative planned dose is >350 mCi (13 GBq), or if they are attempting conception within 18 months of therapy.