A man has undergone surgery and radioactive iodine for thyroid cancer. His wife has 2 months amenorrhoea with UPT negative. The man has been told that the couple should not have a baby for 1 year. Could anybody tell me the reason?

Is it mandatory that the wife of a man who has thyroid cancer should avoid pregnancy? Can sperms become teratogenic on exposure to any of the drugs used for the treatment of thyroid cancer? Kindly suggest.