Answer to Question #11059 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Lead Aprons

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

Q

What is the standard for wearing lead aprons in the Operating room when using a portable x-ray machine or a C-arm? Is there a proper distance to stand away from the machine without wearing the apron?

A

There are actually several answers to this question, depending upon several factors. The first factor is to determine what regulations apply and how your regulatory agency interprets those regulations. An excerpt from the State of Indiana regulations (where the author of this answer resides) which addresses this issue is as follows: 

"(t) Except for patients who cannot be moved out of the room, only the staff and ancillary personnel required for the medical procedure or training shall be in the room during the radiographic exposure. In addition to the patient being examined, others will be protected in the following manner:

(1) All individuals shall be positioned such that no part of the body will be struck by the useful beam unless protected by five-tenths (0.5) mm lead equivalent.

(2) Staff and ancillary personnel shall be protected from direct scattered radiation by protective aprons or whole body protective barriers of not less than twenty-five hundredths (0.25) mm lead equivalent.

(3) Patients who cannot be removed from the room shall be protected from direct scattered radiation by whole body protective barriers of twenty-five hundredths (0.25) mm lead equivalent or shall be positioned so that portion of the body nearest to the tube head is at least two (2) meters from both the tube head and the nearest edge of the image receptor.1"

The Indiana regulations define “direct scattered radiation” as follows:  “As used in this rule, ‘scattered radiation’ means that radiation which has changed direction by virtue of its contact with matter after emerging from the radiation head.” This essentially means the scatter coming from the patient, image receptor, and various components of the operating room table.

Thus, at first glance Indiana’s regulations appear to state that anyone in the room has to wear a lead apron. However, there is a bit of “wiggling room” that can possibly be applied to these regulations. First, for staff and ancillary personnel (that’s what you’re asking about), the regulations mention using protective aprons or “whole body protective barriers.” As such, portable shields could be positioned in the operating room for some individuals to stand behind when the radiograph is performed or when the fluoroscopy unit is activated. That may or may not be practical, depending upon how many individuals are in the operating room and the physical size of the operating room.

Another option is to instruct individuals who don’t wear lead aprons to stand behind someone who does when the radiograph is taken or when the fluoro unit is activated. This could apply to individuals who periodically enter and leave the operating room (e.g., circulating nurses), but aren’t there for the entire procedure. As a way to assure such individuals would receive very little exposure using that approach, you could have them wear a personnel monitoring badge for a period of time (e.g., three months) to see if they receive any exposure and if so, how much. If they would be expected to receive less than 1 mSv in one year (i.e., 0.25 mSv in a three-month period), that would typically be less than what a member of the general public could receive under other parts of the regulations. It would be important to document that information for review by your regulator.

If the individual would be expected to receive more than 1 mSv per year, but less than 5 mSv per year, you should provide some radiation safety training for such individuals and possibly continue to monitor them, either with a standard personnel monitoring badge or an electronic dosimeter.

Unless you do large numbers of radiographs in the operating room, it is the fluoroscopy unit that will impart the majority of the exposure to individuals in the operating room. As a way to look at this from the potential for exposure, one can use the “scatter fraction” that is applied for shielding calculations to estimate the exposure at a given distance from scattered radiation. For example, the fraction of radiation scattered at 90 degrees, 1 m from a patient with a fluoroscopy unit operating at 100 kVp with a circular field size of 410 cm (NCRP 2004) is estimated to be about 0.00195, or 0.195 percent of the useful beam striking the patient1. If one assumes an entrance exposure of 0.00129 coulomb per kilogram per minute (C/kg/min) (5 roentgens per minute) which is reasonably conservative for a portable fluoroscopy system, then the estimated exposure rate at 1 meter would be 0.00195 C/kg/min x 0.00195 or 2.52 x 10-6 C/kg/min (9.75 mR/min). At 3.04 meters, the estimated exposure rate would be about 2.84 x 10-7 C/kg/min (1.1 mR/min). In this context, that would also be about 0.011 mSv min-1.

Thus, to reach 1 mSv in a year, someone would have to be within 3.048 m of the patient for almost 100 minutes a year when the fluoroscopy unit was operating to receive 1 mSv, or 500 minutes per year to reach 5 mSv. As such, another approach could be to require that anyone not wearing a lead apron or not behind a portable barrier be at least 3.048 m away whenever the fluoroscopy unit is activated. One could even mark an area on the floor to indicate the location of that 3.048 m distance. Again, this approach should be supplemented with personnel monitoring in order to indicate how the procedure affects the exposure to such individuals.

So, the first step is to review what your applicable regulations require regarding the need for shielding personnel present in areas where x-rays are generated. Following that review, you can then discuss the issue with your regulators to see what options are available to you to meet the regulations and maintain exposure to your personnel as low as reasonably achievable (ALARA). If you aren’t the Radiation Safety Officer (RSO), this should also be discussed with him/her.

Mack L. Richard, MS, CHP
Director of Health Physic/Radiation Safety Officer
Indiana University Medical Center

References

  • 1410 IAC 5-6.1-118 – General requirements for operation of x-ray equipment.
  • National Council on Radiation Protection and Measurements. Structural shielding design for medical x-ray imaging facilities. Bethesda, MD: NCRP; Report No. 147; 2004.
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