Answer to Question #6116 Submitted to "Ask the Experts"

Category: Pregnancy and Radiation — Proximity to radioactive persons

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


I'm a physician, I'm pregnant, and I will be the caretaker of a patient who will be a post-operative bone marrow treatment patient and total body irradiation. This will be after a five-week hospitalization at the University of Washington. I'm having trouble assessing my potential risk. I will be 20 weeks at the time when she is discharged, and I was told that she would at peak have 0.07 mSv m-1 of 131I, and possibly closer to 0.02 mSv-1 meter two to three days after discharge. I am concerned and want to have the data on this potential risk to make an informed decision about when and how I am to do the caretaking (including IV changes, food preparation, help around the house, etc.) and ways to protect my fetus.


Thank you for your question. I can certainly appreciate your need for data as I am much the same way. The dose rate the patient will emit will depend on the amount of radioactivity that is administered. Patients administered 131I generally can't be released from the hospital until they emit only 0.07 mSv h-1 at one meter so the numbers you have are correct.

We need to consider a couple of things. First, let's consider the amount of exposure you might receive simply from being around the patient. The exposure changes rapidly with distance and linearly with time. The 0.07 mSv h-1 at one meter (100 cm) will be 0.28 mSv-1 at 50 cm or just under 0.02 mSv-1 at 200 cm (2 meters). So whatever you need to do closer than a meter to the patient, plan it out and do it in the minimal time possible. Try to stay at a meter or farther away when you are simply talking with the patient. The radiation exposure from the patient will also diminish as the patient biologically excretes it via urine, plus there is radioactive decay. Within three to four days, the exposure should be about 0.03 mSv h-1 at one meter and within another eight or so days, it would be down around 1 mrem/h at one meter.

The fetal dose limit for someone who is working at a licensed organization is 5 mSv during the gestation period. That might offer some perspective. There are no documented health effects to the fetus at doses below 60 mSv. You can use the information in the second paragraph to estimate your radiation exposure. For instance, if you spend 30 minutes each day at 50 cm plus one hour each day at 100 cm plus three hours at 200 cm or more, your daily exposure would total to about 0.38 mSv in each of the first few days. After that, it would be about 20 mrem per day for the next eight days, and so on. This is not a dose that would affect the fetus.

But now for something I think is more important—you need to know that radioactive iodine is also excreted in saliva and sweat. You really should wear gloves for the first week or so when you handle anything the patient has touched—the linens, silverware, plates, books, TV remote, etc. Those items might have some 131I on them and when you touch them, some of that 131I can get on your hands. Wash your hands often. Don't use the same toilet facilities for the first week. For someone who is not pregnant this isn't an issue and it is a small one even for you, but I would take the precautions so you don't accidentally get the 131I on your hands, then into your mouth and taken internally. Radioiodine will cross the placental barrier if taken internally.

Let me know if you'd like more information. We know a lot about radioactive iodine treatments and we care for many of this type of patient where I work.

Kelly Classic
Certified Medical Health Physicist

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 7 February 2007. 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.