Answer to Question #10054 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 was diagnosed with Graves' disease and was prescribed 629 MBq of radioactive iodine to address my disease. After the 131I intake, I went into self-imposed isolation for 10 days to protect my wife and my almost two-year-old daughter.

After the 10 days, I was told by the hospital nuclear medicine staff that I could go on with my life as normal.

On the 11th, 12th, and 13th days, I spent considerable time with my family and believe that I spent about 3.5 hours watching television by or cuddling my daughter. I estimate that the average distance of her little head to my thyroid was about 15 cm. We also went to lunch and shopped as a family during these three days.

On the 14th day I decided to buy a radiation detector to check whether I was still radioactive. I was very, very frightened to see that I was still radioactive, and am very concerned about the exposure to my daughter on the 11th, 12th, and 13th days. On the 14th, day, I went into isolation again in separate quarters in my house.

  1. Could you please give me advice input on how dangerous was my exposure to my daughter?
  2. Is there any possibility of estimating how much I may have exposed her to?
  3. Are there noninvasive and nonnuclear ways to know how bad was the exposure?

I am very, very concerned and hope that you will answer my questions.


You have not harmed your daughter. You followed the instructions given to you and were isolated even more days than many facilities require.

Radiation detectors are very sensitive and can even detect the cosmic radiation that we are exposed to every day that we live on earth. Being able to detect it is not unusual, even two weeks later since the material that was incorporated into your thyroid will now be decaying by half approximately every eight days.

Hospitals classify the dose given to you for Graves' disease as a low dose. Studies were performed to determine when it is safe for a person treated with radioactive iodine to be around other people. The conservative assumptions that are used to determine when controls can be suspended are based on the Nuclear Regulatory Commission (NRC) regulations to not expose a family member to more than 5 mSv from a nuclear medicine treatment. That is also the total radiation dose that the fetus of a pregnant woman is legally allowed to receive if the mother continues to work in radiation areas while pregnant.

The policy at my facility is for a person who receives less than 1221 MBq to be isolated for the first four days and to avoid holding children for long periods of time for the first week after treatment. Usually more than half the amount of radioactivity leaves the body the first day. Some of the radioiodine concentrates in the thyroid and the remainder is removed in the urine. Your isolation time was greater than my hospital's directions (seven days compared to your 10 days).

It is not possible to estimate the exposure to your daughter and there are no noninvasive nor nonnuclear ways to determine her exposure. To perform an estimate, I would not want to guess how much was in your thyroid since there are so many variables that I don't know, such as, how much uptake you had, how rapidly it left your body, the initial radiation exposure reading and subsequent readings. I feel confident that she was exposed to much less than 5 mSv, especially since distance was kept for 10 days and then you isolated yourself again after you became concerned. And, as I said earlier, 5 mSv is considered a safe dose for a baby in the womb. It is certainly safe for a two year old.

I can understand your fears and concerns. However, given our many years of experience treating patients with radioiodine, I believe that no harm was done to your daughter.

Marcia Hartman, MS

Answer posted on 12 January 2012. 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.