Answer to Question #3717 Submitted to "Ask the Experts"

I have recently had radioactive iodine treatment as I have an overactive thyroid. I am planning a holiday in several months and am concerned that I will still be slightly radioactive and will set off radioactivity equipment at the airport. I have read that this can happen up to 14 weeks after having the treatment. Can you advise?

The radioactive iodine-131 used to treat thyroid disease has a half-life of eight days. So, in approximately 80 days or a little over 11 weeks, the original quantity will undergo significant radioactive decay and convert itself to something that is not radioactive. Between now and your trip, very little, if any, radioactive iodine will be left in your thyroid gland. Security screeners have become accustomed to detecting radiation coming from individuals who have undergone nuclear medicine procedures. If they detect any radiation coming from you, they should be able to pinpoint it as coming from your thyroid gland. If they do detect any, your telling them that you had a radionuclide therapy procedure should be sufficient. If you are overly concerned about this, you could ask the nuclear medicine department that did your procedure to issue you a letter that tells when your procedure was performed and the nuclide and activity used. Relax and have a safe and enjoyable holiday!

Kenneth L. Miller, CHP

Editor’s note: As an example of the decay mechanism, if 1,000 atoms are detected on the first day, 500 atoms will be detected after eight days. After 16 days, only 250 atoms will be detected, with the numbers being halved after each eight days.