Answer to Question #134 Submitted to "Ask the Experts"

Q

I am working as an operating room nurse and am about 16 weeks pregnant. Every once in a while my job requires that we use a C-Arm or an image intensifier which allows you to see the objects inside a person's body, in motion. Of course I try to be out of the room as much as possible and I also follow the precautionary measures. But still I'm concerned about what effect it might have, if any, to my baby. I hope you can help me on this topic.

A

As with all x-ray procedures, employee exposure is from a scattered x-ray beam—only the patient should be exposed to the primary beam. In portable fluoroscopy (i.e., a C-Arm) several items impact the amount of exposure you receive while in the room. I’ll take each one separately, then put them together to estimate a dose rate for a given circumstance.



Individuals in the room during a diagnostic or fluoroscopic x-ray exam are required to wear a lead apron. A lead apron of 0.25 mm lead equivalent thickness will stop at least 90 percent of the x rays and a 0.5 mm lead equivalent apron will stop at least 97 percent of them. You can check the lead equivalence of an apron by looking at the inside tag. How the C-Arm is positioned can also affect the amount of radiation exposure received. For instance, if it is a vertical projection with the x-ray tube underneath the table and patient (the image intensifier is above the patient), then even the scatter x rays must pass through the patient to get to you. That translates to less exposure. If the C-Arm is positioned to do cross-table fluoroscopy, it gets a bit trickier. The higher areas of exposure during a horizontal projection will be (1) next to the table, next to the x-ray tube and (2) next to the image intensifier. It is preferable to avoid these two locations if possible.



The third item that impacts the amount of exposure received is distance. Distance plays a significant role in minimizing exposure. Keep in mind that it is distance from the site of interaction of the x rays and the patient. For instance, if the beam is entering the patient at the chest level and you need to be next to the table, you can minimize your exposure just by moving down toward the patient's feet. So you don’t always have to back away from the table, but if you can do that, get as far back as possible. With these three things in mind, let’s look at two general fluoroscopy scenarios. We’ll assume standard fluoroscopic settings on the x-ray console. First with the tube under the table and image intensifier overhead (vertical projection): without an apron, right next to the table, you could receive 1 mrem/min (most fluoroscopy times are seconds long); at 1 meter (3 feet) it would be about 0.2 mrem/min and at 2 meters about 0.1 mrem/min. With a 0.5 mm apron, these numbers would be 0.03 mrem/min next to the table, 0.006 mrem/min at 1 meter and 0.003 mrem/min at 2 meters. With a horizontal projection, these numbers change slightly. If during the fluoroscopic procedure you are standing without an apron next to the table and next to the tube, the dose rate would be 2 mrem/min (0.06 mrem/min with a 0.5 mm apron). If you backed away from the tube 1 or 2 meters, the dose rates are the same as the above example with a vertical projection. With a lead apron, there is no known biological effect for you or your baby from this amount of radiation. You indicate you leave the room when possible–that is the best advice for any employee to reduce exposure. But if you must be in the room during the exposure, be sure to maximize distance when possible and to wear a lead apron. Just a side note: the dose limit for a fetus of a declared pregnant worker (someone occupationally exposed to radiation who tells the institutional Radiation Safety Office of her pregnancy) is 500 mrem during the entire gestation period.



Kelly Classic

Certified Medical Health Physicist