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Safety
5 Steps to Improved C-arm Safety
Glenn Sturchio
Publish Date: October 10, 2007   |  Tags:   Staff Safety

Safe C-arm use depends on two aims: optimizing the radiation dose that the patient receives and minimizing the radiation dose that the equipment operators and surgical staff are exposed to. You want to generate the least radiation necessary to obtain usable images. This thinking is summed up in the acronym "ALARA," or "as low as reasonably achievable," a sort of cost-benefit philosophy for radiation safety. Here are five principles toward reaching the goal of safe C-arm use for your orthopedic, pain management, urological or other procedures.

Consult an expert.
Even though they've become common in surgery center ORs and procedure rooms, C-arms are clearly not just plug-and-play equipment. As interventional radiological devices, they're regulated by state authorities and require state, and sometimes local, assessments. That's one reason why it's essential to involve a qualified, board-certified health or medical physicist who's familiar with the equipment and regulations during several stages of the C-arm process.

If you're considering the purchase of a C-arm, the physicist can assist in the selection. His knowledge of the latest advances in imaging technology, coupled with an awareness of your center's case mix and intended use of the equipment, can provide you with insight on the most appropriate unit and features for your facility.

The physicist also plays a key role in determining the shielding required to confine and control radiation levels in areas adjacent to your procedure room, a calculation that's particularly important if your facility occupies space in a multi-purpose structure such as a professional building or a commercial development. He can also provide a radiation protection survey for your facility, if one is required.

The service and maintenance of a C-arm depends largely on its usage - the higher the usage, the more frequent the service. It also depends on the physicist, since it's not typically the manufacturer's service rep who makes the decisions on necessary repairs. The physicist will perform a quality assurance evaluation annually (or more frequently, if high usage makes that necessary) and identify what repairs need to be undertaken for your C-arm's optimal operation and regulatory compliance.

Your C-arm's manufacturer might not be able to recommend a health or medical physicist, but your state's radiation protection office, local regional hospitals or universities, the professional organizations you're affiliated with, the American Association of Physicists in Medicine (www.aapm.org) or the Health Physics Society (www.hps.org) may be able to provide you with a list of consultants in your area.

Protect your surgical staff.
C-arm operators can avoid direct exposure to radiation by keeping their hands out of the fluoroscopic beam, of course. Avoiding indirect exposure, however, requires adequate shielding on their persons and perhaps installed in the OR.

Surgical staff should wear well-fitted protective garments to shield their torsos. Aprons, vests, skirts and thyroid shields containing 0.5mm lead equivalent material are appropriate for attenuating 90 percent to 95 percent of scattered X-rays at typical diagnostic energies. These protective garments are required by law when operating fluoroscopic devices, but their use should be common sense. Leaded glasses with side shields or protective goggles are options for reducing radiation exposure to the eye.

When you're equipping your facility with shielding garments, it's important to select and provide items that offer thorough protection but that are also comfortable. Put simply, you can buy lead aprons that are torture to wear or others that are designed smarter and, as a result, will get worn more often. Some leaded garments are supported solely by the wearer's shoulders, while others include a hip belt for support. If you've ever been backpacking, you know how much weight a belt can shift off of your shoulders.

Moveable shields can also offer protection against exposure. Small, leaded window panels can be suspended from the ceiling on articulated arms that let them be maneuvered between the patient and surgeon during cases.

Alternatively, larger, portable leaded windows, about seven-feet high and four-feet wide, can be placed around the room for personnel to shelter behind when imaging is being conducted.

Be mindful of patient and staff positioning.
Another important issue in dealing with radiation exposure is the positioning of the patient and surgical staff in relation to the imaging equipment.

For C-arm-type fluoroscopy units, the patient should be positioned as far from the X-ray tube as practicable in order to minimize the patient's entrance skin exposure. Additionally, the image receptor should be positioned as close to the patient as is possible. This also lowers the patient dose and results in a sharper image as well.

Operators should limit the use of magnification features that require the patient to be moved closer to the X-ray tube and further from the image receptor, since these functions significantly increase the patient's radiation dose.

The primary source of occupational exposure during fluoroscopic imaging is not actually the equipment, but the patient. The surgical staff is exposed to radiation that scatters back toward the X-ray source from the surface where it enters the patient. Those closest to the patient's body stand to receive the greater dose, while those at some distance will receive lesser doses as the radiation level drops off. Therefore, surgical personnel should step back from the table when possible (for instance, while digital images are acquired) in order to reduce their exposure.

Another way the operator and surgical staff can reduce their exposure is by standing on the image receptor side of the table when possible. This may seem counterintuitive, since then they'll be facing the X-ray tube, but radiation levels on the image receptor side are actually significantly lower. If the unit produces a vertical X-ray beam, the image receptor should be above the table and the X-ray tube below it, to reduce personnel exposure.

Occupational radiation monitoring is required by state regulations. If personnel are likely to exceed the threshold stipulated in the regulations, it is likely that the operator and some members of the surgical staff will be required to wear personnel monitoring devices such as dosimeters or exposure badges.

Optimizing exposure time.
Managing fluoroscopy time is another elementary but key step in C-arm safety. It's a risk-benefit balance. The longer it takes a surgeon and equipment operator to acquire a diagnostic image, the more radiation the patient and surgical personnel potentially receive.

While fluoroscopy time depends largely on skill - a seasoned surgeon will be able to complete a procedure requiring imaging in less time than it takes someone with less experience - equipment use and functions also play a part.

Limit image acquisition to what's necessary for the diagnosis and documentation at hand. Since fluoroscopy's radiation exposure rates are higher than those of X-rays, for instance, you shouldn't use a C-arm when diagnostic X-rays would suit the purpose. You can also use a machine's last-image-hold function to review anatomy without generating more radiation.

Pulse fluoroscopy, a function available on most imaging equipment, takes advantage of the human eye's integration time to reduce the radiation dose generated. While a C-arm can capture and deliver 30 frames per second, the human eye can't perceive every individual image at that speed. Pulse fluoroscopy uses a lower frame rate and as a result generates less radiation. The eye won't generally notice the resulting flickering until the imaging speed slows to 15 frames per second. Even at 7.5 frames per second, the imaging may still adequately serve diagnostic purposes. Plus, it will do so at only 25 percent of the radiation dose of the 30 frames-per-second setting.

A dose-area product monitor will record how much radiation has been delivered during an imaging session, but it's important to note that it doesn't measure the size of the dose that the patient's tissue has received, especially if the field of view has been moved or adjusted during the procedure. Only use the monitor's report as a relative value.

Control by collimation.
The size of the radiation field also plays a role in safe C-arm use. Don't irradiate tissue that doesn't need to be irradiated. By minimizing the size of the imaging field of view - a technique known as collimation - to the area of greatest clinical interest, you're reducing the cross-section of the X-ray beam that's hitting the patient and limiting the volume of tissue that's irradiated. Reducing the cross-section of the X-ray beam also reduces the radiation level in the OR, thereby reducing occupational exposure. This also improves the resulting image quality, as it reduces the scattered X-rays that blur images.

Efficiency with safety
The advantages that C-arm imaging offer has made it standard practice in hospitals and many surgery centers. Emphasizing the options available to protect patients and surgical personnel against radiation exposure can make efficient diagnosis a safe process.

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