Answer to Question #11860 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 had radioactive iodine treatment 13 days ago with a dose of 4,625 megabecquerels (MBq). As far as being around other people, I was told to observe seven days of restrictions and then on the eighth day I could go back to normal and go back to work (I am back to work now).

But when I received the portable Geiger-Mueller (GM) counter I ordered, I found I'm still "hot" about 1 meter away. I also read on multiple websites about contamination from body fluids of everything you touch. The "touch" thing is what I'm worried about for my family, especially for my two children (12 years old and 6 years old). I was told by my doctor that unless I'm sweating like crazy (and she even touched my hands), I shouldn't have to worry about contamination.

I am not saying that I don't believe my doctor, but I am asking for a second opinion. As of now, I'm still keeping myself in isolation in our master bedroom (just like the first seven days), but once in a while I get out to see my family just to say "hi" and "bye" from a distance and wearing gloves. I think I should wait another two weeks before I go back to being around my family. What do you think? Am I being paranoid about this?


Radioactive iodine (RAI) therapy for thyroid cancer has been used since the 1940s and is generally a simple and successful procedure. That is good news! RAI therapy does use a radioactive drug, but if the patient follows instructions provided by the doctor, RAI is considered safe for the family of the patient and ultimately for members of the public. The radioactive half-life of RAI (iodine-131 [131I]) is eight days (after eight days, half of the iodine has decayed away), and the biological half-life of 131I in the human body is less than that.

Most of the radioactive contamination is found in urine, and the remainder comes from other fluids such as sweat. If hands are not sweaty and hands are washed after restroom use, contamination is very unlikely to be spread by the fingers. Items that come in contact with the body, like bed sheets or kitchen utensils, can be washed, removing most of the contamination. After a few days the elimination of radioactive iodine through bodily fluids is complete and a small remainder of the drug remains "fixed" in body tissue.

Because the drug is radioactive, its use is regulated by the Nuclear Regulatory Commission (NRC). Patients are permitted to leave the clinic only when the doctor ensures and documents that the radiation exposure to the family will be below a certain limit for the whole "life" of the drug, meaning all of the half-lives of the radioactive iodine, even beyond the days of specific restrictions. This means the exposure to the family is kept low, but it is not zero. The world has natural radiation that we are always exposed to, and family exposure is kept to levels that are similar to what we are exposed to naturally.

Your questions regarding measurements made with a GM counter are tricky. Purchasing a GM counter has pitfalls. Was it calibrated correctly? Was it shipped correctly? How was it calibrated? Different radionuclides such as 131I can cause the instrument to overrespond; some radionuclides cause the instrument to underrespond. The observed counts per minute were not included in your question, which raises more questions. Natural background radiation is measurable by GM counters. The ticking of natural radiation is one of the ways health physicists check the proper function of a GM counter.

Additionally, materials like porcelain (found in toilets and sinks), ceramic tiles, and granite countertops have higher levels of natural radiation and can be detected by a GM counter. Natural radiation and the proper function of a GM instrument aside, there is another issue: because 131I has an eight-day half-life, contamination may be detectable for several weeks and is not an unexpected finding after this procedure.

So in the end, if you follow the doctor's instructions, it is safe for your family and coworkers to discontinue the restrictions when the time comes. The limits set by the NRC are conservative and protective. However, while it is unnecessary, it is certainly fine to continue implementing the restrictions for an extra few days if you feel more comfortable that way. Your doctor is always available to answer questions or concerns. And also, we at the Health Physics Society "Ask the Experts" feature are always happy to provide additional information.

Hopefully the above information answers your questions and concerns, and you are back to your normally scheduled life!

Dawn Banghart, CHP

Answer posted on 20 March 2017. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, 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. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.