Answer to Question #324 Submitted to "Ask the Experts"

Q

I am a female nuclear medicine technologist concerned about radiation exposure during pregnancy. What exams should I be exempt from? Our department handles alot of cardiac (²⁰¹Tl as well as sestamibi) and bone patients as well as thyroid uptakes and scans. I have also heard that secondary scatter radiation produced from the interaction of the gamma rays and the lead apron may be harmful; I haven't come across any literature regarding this matter. Would it be better to wear a lead apron or stand behind a lead shield? Should I be wearing the lead apron throughout the pregnancy or during certain times? Is it necessary to wear the apron all day or just during certain procedures? Is an apron adequate or would a full vest be better? I would also appreciate it if you could direct me to some literature which would provide guidelines on this subject. Thank you!

A

First, let's take a look at the exposure you might expect to receive from patients administered some of the routine radiopharmaceuticals. Information in this table is taken from a National Council on Radiation Protection and Measurements (NCRP) report, Report 124, titled Sources and Magnitude of Occupational and Public Exposures from Nuclear Medicine Procedures.

The exposure limit for the fetus of a woman who is occupationally exposed is 500 mrem during the gestation period. According to the NCRP Report 124, most nuclear medicine technologists receive less than 100 mrem in one year. You should contact the individual(s) at your institution who track your radiation exposure history to find out what level of exposure you have been receiving to determine if you might approach a level that would require you to change your work habits. That said, I'll take your questions one by one.

What exams should I be exempt from? Because the exposure from patients who have been administered radiopharmaceuticals is quite low, there is no radiological reason not to continue imaging procedures. If your institution administers therapeutic activities of ¹³¹I for thyroid cancer, you might consider refraining from this particular part of your practice. Not only are there higher exposures associated with the administration of ¹³¹I, but iodide is volatile, increasing the potential for internal uptake.

I have also heard that secondary scatter radiation produced from the interaction of the gamma rays and the lead apron may be harmful; I haven't come across any literature regarding this matter. This wasn't a question but I thought I'd address it anyway. What you might be thinking about is x rays that can be produced when beta particles (from ³²P or ⁹⁰Sr) interact with lead. I'm not aware of any harmful interaction between gamma rays at the energies used in nuclear medicine and lead.

Would it be better to wear a lead apron or stand behind a lead shield? Should I be wearing the lead apron though out the pregnancy or during certain times? Is it necessary to wear the apron all day or just during certain procedures? Is an apron adequate or would a full vest be better? A lead apron won't be necessary if you are only imaging patients but if you choose to wear one, it is most effective only for the lower energy radionuclides, e.g., ^99mTc or ²⁰¹Tl; it won't provide much shielding for ¹¹¹In or ¹³¹I. A 0.5 mm lead equivalent apron (there should be a tag on the apron specifying the lead equivalency) will stop about two-thirds of gammas from ^99mTc or about 90 percent of the gammas from ²⁰¹Tl. Instead of wearing an apron, you would strongly be encouraged to shield the source by using syringe shields or lead containers for the vials. The lead apron, along with the pregnancy itself, can cause stress and pain in the back muscles. Again, if you choose to wear one, a skirt style covering the lower abdomen would be adequate.

I would also appreciate it if you could direct me to some literature which would provide guidelines on this subject. The NCRP document I mentioned in the first paragraph might be of interest and can be obtained by writing to NCRP Publications, 7910 Woodmont Avenue, Suite 800, Bethesda MD 20814-3095 or visiting their Web site. You might also want to visit the Nuclear Regulatory Commission web site to look at their regulatory guide on prenatal radiation exposure when the mother is occupationally exposed.

Kelly Classic
Certified Medical Health Physicist