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21 November 2009

Answer to Question #4985 Submitted to "Ask the Experts"

Category: Radiation Workers — Pregnant Workers

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

I am a nuclear medicine technologist and I am 16 weeks pregnant. Recently I have been asked by my supervisor to do a rotation in the PET/CT department. I have looked on the Internet to find any articles on the risks of PET exposure and there aren't very many. I would like some advice on this topic if possible.

It's great you're trying to find out if there are additional risks from working in a PET (positron emission tomography) area and you're right, there isn't too much information available that is easily accessible. The risks of working in a PET area aren't very different than those from working in a nuclear medicine area. You want to make sure you don't become internally contaminated with any radioactive material—that is the dominant factor of working in either area—so the protection remains wearing gloves, lab coat, etc., and surveying yourself after you handle materials.

The other item that remains the same is that most of your exposure will come from the patient who has been administered the radioactive material. This is actually where the difference comes in as well because the positron emitters emit higher-energy photons than most of the radioactive materials used in general nuclear medicine. That, in combination with the fact that positron emitters have very short half-lives so patients are administered more activity, means patients emit more radiation.

Let's compare a 20 mCi dose of ^99mTc to a 20 mCi dose of ¹⁸F (fluorine). The dose from the patient right after injection of the ^99mTc would be around 2 mR/h at 1m (National Council on Radiation Protection and Measurements Report 124). The dose from the patient right after injection of the ¹⁸F would be around 10 mR/h at 1m. Neither dose is considered harmful to you or to your pregnancy but you can see why it is important to maintain your distance from patients after injection, especially those who are administered positron emitters. The radiation dose from the ¹⁸F will drop dramatically with time due to excretion and the short (about 2 h) half-life.

So, the risk of working in a PET area is the potential for higher occupational exposures depending on how many patients are seen, though still well within regulatory limits. By following standard radiation protection procedures—time and distance—there should be no additional risk for someone who is pregnant.

Kelly Classic
Certified Medical Health Physicist

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