Answer to Question #301 Submitted to "Ask the Experts"

Q

I am a speech pathologist and perform approximately two modified barium swallows a day, four times a week. I hope to to start trying to become pregnant soon. My question is about safety guidelines for being pregnant and observing modified barium swallows being performed under fluoro. If I wear a lead apron and stand behind a lead wall am I placing the baby in any type of danger or increasing the risk of of birth defects, cancer, etc.? I will not be observing the swallows the first trimester.

A

Without getting into a lot of detail, because of the precautions you are taking you are not placing the baby at any additional risk. Now for the details, in case you want to know. The lead equivalency of most aprons today is 0.5 mm; these attenuate the primary beam by about 96-97 percent. While you are exposed to less energetic, secondary scatter radiation and not the primary beam, I quote primary beam information because that is how lead apron adequacy is checked. The lead thickness in most standard diagnostic x-ray walls is 1-1.5 mm so at least 99 percent of the primary beam is stopped.

With that in mind, let’s look at room exposure during a barium swallow. I’m going to use data from my institution and I hope you can extrapolate it to your situation. The fluoroscopy time for our swallows lasts about five minutes total over the entire procedure, and we videotape part of the procedure which increases the dose. The output of our equipment under these conditions is about 2.5 R/min for a total of 12.5 R (12,500 mR) to the patient’s skin over five minutes. Literature and some measurements we’ve taken here suggest that if you stand right next to the table while the fluoroscopy is on, you will receive about 1percent of what the patient gets. At one foot, it’s about 0.1 percent and at one meter, it’s about 0.01 percent. Let’s put all the numbers together. The patient gets 12,500 mR total so if you stand right at tableside, you could get 125 mR with no apron and 5 mR with an apron. Standing at one foot, you could get 12 mR with no apron and 0.5 mR with an apron. At one meter, you could get 1 mR with no apron and 0.05 mR with an apron. You can multiply these by eight to obtain the exposure you receive each week. From your question it appears that you can be at least 1 meter away. If you’re also behind a lead wall, the exposure is about 10 times less than what we’ve calculated here. If you are able to stand at least 1 meter from the patient during the fluoroscopy and wear a lead apron, your annual exposure (under the apron) would be approximately 20 mR. This is well below levels of radiation reported in literature that have potential to cause fetal biological effects. I can also share with you that we give pregnant employees a radiation badge to wear at their waist under their lead apron. Most of these employees are in x-ray areas—some in areas where a significant amount of fluoroscopy is used. We have never had a reading on a badge worn under the apron at the abdominal level for a worker in an x-ray area.

Kelly Classic
Medical Health Physicist