Answer to Question #11759 Submitted to "Ask the Experts"

Category: Nuclear Medicine Patient Issues — Diagnostic Nuclear Medicine

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

Q

I have scoured your site and much of the internet, but I have not found any specific answers to alleviate my maternal anxiety. I recently had a hepatobiliary (HIDA) scan done and received about 190 megabecquerels (MBq) of technetium-99m (99mTc) Choletec. I was injected around 8:30 a.m. I finished up around 10:40 a.m. and went home to rest. Around 12:20 or 12:30 p.m., my husband brought our five-year-old son home, and my son sat on a large pillow on my lap for around five to seven minutes. After that initial five to seven minutes with my son sitting on the pillow on my lap, I was able to almost completely stay in a separate room from my son for the rest of the afternoon.

I didn't think much about this until I started looking at HIDA radiation exposure and children on the internet. Now I am beside myself with guilt and worry. I called and spoke with someone at the testing facility about my concerns, but I felt like a nuisance and I did not push for a satisfactory answer that explained the risk, if any, at which I put my son. So much information on the internet makes me think I did something to put my son at risk. How much radiation did I expose him to and what are the risks from that exposure? Any specific advice to a very concerned mother would be appreciated.

A

You can stop worrying, and there's no need to feel guilty. No harm has been done, and you have not put your son at risk. I cannot determine exactly what your son's effective dose was from those five to seven minutes, but I can estimate it, if you don't mind following along with me.

There are regulations which specify when a patient who has been administered radioactive material can be released from the hospital. The release criteria are based on the radiation exposure to other people, and it is set at 5 millisieverts (mSv). For 99mTc, the administered activity that would result in a 5 mSv dose to others is more than 28,000 MBq. You received only about 190 MBq, which is less than 0.7% of 28,000 MBq. By simple ratio, the 99mTc you received would have resulted in a dose of 0.03 mSv to other people. By the way, your dose as a patient would be around 3 mSv.

The amount of administered radioactivity to result in a 5 mSv dose to other people was calculated using some assumed conditions. One of the assumed conditions is that the other person is 1 meter (m) away from the patient for the entire period. Since your son was closer but only for five to seven minutes, an adjustment needs to be made for both distance and time. (The other assumed conditions make this calculation an overestimate of his dose, so to err on the side of caution, we will not adjust them.) After adjustments for distance and time, your son maybe received 0.005 mSv from being close to you for that short time. This is less than the natural background radiation you and your son are exposed to each day.

Kent Lambert, CHP, FHPS

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