What protection do we need to use whe having after radioactive iodine therapy?

i know we cant have or close contact for 16 days after the treatment but then I understand we have to use protection for for up to 12mths. what i need to know is whether this is just to prevent pregnancy or is it dangerous for sperm to enter me at all during the next year. If it is just to prevent pregnancy can I then just use contraceptive pill as before rather than condoms?