Long-term male fertility after treatment with radioactive iodine for differentiated thyroid carcinoma

Context: Whilst radioactive iodine (RAI) is often administered in the treatment for differentiated thyroid carcinoma (DTC), long-term data on male fertility after RAI are scarce.Objective: To evaluate long-term male fertility after RAI for DTC, and to compare semen quality before and after RAI.Design, setting and patients: Multicenter study including males with DTC >= 2 years after their final RAI treatment with a cumulative activity of >= 3.7 GBq.Main outcome measure(s): Semen analysis, hormonal evaluation, and a fertility-focused questionnaire. Cut-off scores for 'low semen quality' were based on reference values of the general population as defined by the World Health Organization (WHO).Results: Fifty-one participants had a median age of 40.5 (interquartile range (IQR): 34.0-49.6) years upon evaluation and a median follow-up of 5.8 (IQR: 3.0-9.5) years after their last RAI administration. The median cumulative administered activity of RAI was 7.4 (range: 3.7-23.3) GBq. The proportion of males with a low semen volume, concentration, progressive motility, or total motile sperm count did not differ from the 10th percentile cut-off of a general population (P = 0.500, P = 0.131, P = 0.094, and P = 0.500, respectively). Cryopreserved semen was used by 1 participant of the 20 who had preserved semen.Conclusions: Participants had a normal long-term semen quality. The proportion of participants with low semen quality parameters scoring below the 10th percentile did not differ from the general population. Cryopreservation of semen of males with DTC is not crucial for conceiving a child after RAI administration but may be considered in individual cases.