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

Category: Nuclear Medicine Patient Issues — Therapeutic Nuclear Medicine

The following question was answered by an expert in the appropriate field:

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.

Answer posted on May 13, 2004. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.