Answer to Question #11804 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding

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

Q

What are your recommendations for staff members in the operating room (OR) for wearing dosimeters? Some ORs are minimizing dosimeter use due to cost and low chances of radiation exposure. What are the chances of getting too much radiation during C-arm fluoroscopy procedures?

A

Personnel monitoring requirements are driven by state regulatory agencies and vary somewhat from state to state. Typically, personnel monitoring is required if individuals are likely to exceed 10% of the occupational dose limit. Thus, one must determine if such individuals meet this threshold.

In addition to the dose limits, most state agencies require protective devices (e.g., lead aprons, lead thyroid collars, lead glasses, etc.) when individuals are within a certain distance of an x-ray-producing device such as a C-arm fluoroscope. Lead aprons and any other protective devices cover most of the body and greatly reduce any whole-body exposure. Thus, most of the body receives only a few percent of any exposure measured by a personnel monitoring device worn outside the protective devices along with parts of the body not covered by protective devices.

Some states allow the use of a correction factor to account for the protection provided by lead aprons to arrive at the effective dose equivalent (EDE) which is compared to the whole-body dose limit. A typical correction factor used when a single personnel monitoring device is worn at the collar level outside the lead apron is 0.3. As such, multiplying the badge reading by 0.3 provides a calculated estimate of the EDE, which would then be compared to the regulatory limit for the whole body. It is important to verify that your state agency allows this type of correction.

There are also limits to the lens of the eye, the skin, and the extremities, but those limits are higher than the whole-body limits. Even so, a personnel monitoring device worn at the collar level outside the lead apron also serves as an estimate of the radiation dose to the eye lens (if no lead glasses are worn), any unprotected skin, and/or the thyroid (if a thyroid collar is not worn). Exposures to the extremities (i.e., the hands) are typically measured by ring dosimeters and are required if the hand dose is likely to exceed 10% of the extremities limit.

So, with all that said, one has to determine if individuals in the OR are likely to exceed 10% of any of the aforementioned limits. That's not necessarily an easy question to answer. It is mainly driven by a number of factors, the first being how frequently radiation is used in the OR—several times a day, several times a week, once or twice a week, or perhaps a few times a month. Obviously, the more frequent the radiation use, the greater the likelihood of exposure. Another important aspect, in addition to the frequency of use, is the length of time the x-ray unit is operating for the individual cases. Longer "on times" result in higher exposures while shorter "on times" will result in lower exposures. Finally, another very important factor is how close individual staff members are to the x-ray unit and the patient when the unit is operating. Generally, individuals who are more than 1 meter (m) away and wearing a lead apron are not likely to receive much exposure, even if those exposures are relatively frequent.

Here at our institution when we're unsure of the need to monitor a specific group of individuals, an approach we've taken is to monitor a few key individuals in the OR for a finite period of time (say three months). Certainly, you want to select individuals who are indeed within 1 m or less of the patient when the x-ray device is operating. It may also help to monitor a couple of individuals who aren't that close to the procedure, just for comparison. One thing to remember about using this process is to select individuals who are cooperative and will indeed wear the personnel monitoring devices as instructed. They should also keep track of the number and type of procedures performed during the test monitoring period. More information is better (e.g., having them keep track of the fluoroscopy time), but that sometimes gets cumbersome and they may not be very diligent in doing that. Just knowing the number of procedures and getting an idea of the typical fluoroscopy time for those procedures should suffice. It is also helpful to know what protective devices (e.g., lead aprons, lead thyroid collars, lead glasses, etc.) the monitored individuals wear during the procedures. It is also important that they all wear the monitoring devices the same way (e.g., at the collar, outside the lead apron/thyroid collar).

Once the monitoring period has passed, have the monitors processed and compare the "raw" readings (i.e., not corrected in any way) with the various dose limits. If the uncorrected readings are less than 10% of the lowest occupational limit (i.e., for the whole body), personnel monitoring is really not necessary, mainly because the whole-body limit is the lowest of the occupational limits and the lead apron is reducing exposure to most of the body even further. If the uncorrected readings exceed 10% of the whole-body occupational limit, then you can consider making some corrections for lead aprons if your state allows that and compare that to 10% of the limit. You would also need to compare the uncorrected reading to 10% of the higher occupational limits (e.g., extremities, skin, and eye lens). If the whole-body corrected value or the uncorrected value to the unshielded body parts exceeds 10% of any of those the annual limits, you would want to monitor any individuals who might be in that category—likely those within 1 m of the x-ray device or patient. Even when some individuals are not routinely monitored, it is important to review the data from the close-proximity individuals who are monitored to see if their levels have increased to the point where monitoring of individuals farther away is justified.

Finally, the results during the trial monitoring period should be well documented and include the monitoring results, any corrections applied for personal shielding, the percentage of the occupational limits, the number of procedures performed during the monitoring period, and the typical fluoroscopy time during those procedures. Of course, there's some interpretation that has to be applied. If any of the aforementioned results are close to 10%, you may want to monitor those individuals, simply because the number of procedures may vary over time. This report can be used to justify the need for personnel monitoring to individuals and administrators. Conversely, the report can also support the fact that personnel monitoring is not required should regulators or others question why personnel monitoring is considered unnecessary.

If the results indicate that monitoring really isn't necessary, you should periodically (e.g., once a year) check to make sure the number of procedures and/or fluoroscopy time haven't changed appreciably and that you are not excluding anyone who is likely to receive more than 10% of the allowable occupational dose.

Mack L. Richard, MS, CHP

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