The Risks of Radiation
Scatter-the radiation that bounces off the patient-is the primary source of radiation to OR personnel. The exact amount of exposure depends on exposure time, distance from the source, and shielding. The primary health risks to staffers exposed to radiation include cancer, cataract formation, and fetal deformities.
- Cancer risk. The U.S. National Council of Radiation Protection and Measurements (NCRP) estimates that, if 1 million people were exposed to 1 rem of radiation during a lifetime, cancer deaths would increase 0.2 percent, from 190,000 to 190,400. (A "rem" is a unit of radiation dose that quantifies the potential effect of radiation on humans, whereas the more commonly recognized "rad" is the energy imparted per unit mass of tissue. For our purposes, 1 rad equals 1 rem.) To put this in perspective, our natural background exposure to radiation is approximately 0.36 rem per year, and the typical c-arm emits an average of 2 rem per minute. Fortunately, research shows that the average radiation exposure from fluoroscopy to the surgeon during each ACL repair is only approximately 0.0016 rem. In our facility, 90 percent of our staffers who work with radiation receive less than 0.1 rem of radiation exposure each year. Still, experts generally agree that there is no "safe" radiation dose. We do know, however, that the possibility of a biological effect is higher when there is a high exposure in a short time. When exposure occurs intermittently and over a longer time, some damaged cells can repair themselves between exposures.
- Cataracts. Single doses of 200 rad induce cataracts, but people can tolerate doses of up to 750 rads or more without developing cataracts when they accumulate the radiation over time. Although the risk is relatively small, fluoroscopy operators should be aware of it because the lens of the eye, if unprotected, often receives the most radiation exposure.
- Fetal deformity. When a staffer is pregnant, the risk of radiation-induced genetic defects is highest when the baby's organs are forming, between the 4th and 15th gestational weeks. Fortunately, although the fetus is more sensitive to radiation than the mother, the mother's abdominal tissues help shield the fetus. Because there is some type of abnormality in approximately 10 percent of all live births and since occupational exposures are low, it is difficult to correlate a mother's radiation exposure with fetal deformity. Nevertheless, the pregnant physician, nurse, or technician should take special care to ensure proper protection.
Place the Tube Inferiorly
Just as a ball decelerates after it bounces off a wall, radiation rapidly loses its energy as it scatters within the patient. Following this same logic, scatter radiation levels are highest at the point of primary beam contact with the patient; i.e., the side of the "C" that houses the x-ray tube. This is why it is important to place the x-ray tube below the table or patient. This will direct the highest levels of scatter radiation down toward the floor and away from the operator's torso, neck, and head. In addition, physicians who routinely use fluoroscopy with the x-ray tube above the patient have a greater tendency to put their hands in the primary beam, which can lead to epidermal degeneration of the hands and browning fingernails.
Step Away from the Source
OR personnel should distance themselves from the source of scatter whenever possible. Because radiation quickly loses intensity as it travels through the air, standing just one step further away from the source during fluoroscopy can cut surgeon exposure by a factor of four. In fact, OR personnel who stand one foot away from the source will receive less than 1 percent of the dose in scatter. This does not mean the tech or scrub nurse needs to move one foot away from the operating table. Rather, moving just one foot down the length of the table, away from where the beam enters the patient, confers the same protection. This step is important because many people incorrectly intuit that there is more scatter radiation near the image intensifier side of the ?C' where the beam is directed.
Consider the Scatter Profile
As the c-arm tilts, the scatter profile also tilts, and levels of scatter radiation that reach the operator can increase up to four times when the radiation is directed at an oblique angle. This is most relevant when the image intensifier side of the "C" tilts away from the operator, because the unshielded head and neck receive more exposure. The waist also receives more exposure with the c-arm in this position but is protected by a lead apron. Conversely, when the image intensifier tilts toward the operator, the operator's legs and feet receive more exposure. If your surgeons are performing a lot of procedures with this former configuration and the operator or surgeon is unable to step away from the scatter, consider thyroid protectors and specialized leaded glass spectacles. Standard eyeglasses do not protect the eyes from radiation.
Reduce Beam On-Time
- Track beam time. C-arms have a 5-minute timer to help track beam time, and the facility should require the operator to use this function to log cumulative fluoro time. The administrator can then use this information as a quality improvement tool.
- Use last-image hold. C-arm operators will sometimes continuously depress the foot pedal even when they are intermittently viewing the image, or when they need to study a static image. In either case, the operator should revert to saved screen images. Prolonged observation will not improve image brightness or resolution, and these short "looks" usually accomplish the same goal as a continuous exposure. This last-image hold feature can greatly reduce the radiation dose.
- Use pulsed mode. The pulsed mode emits radiation intermittently, rather than continuously, to produce images. This mode can reduce radiation exposure two- to five-fold.
Limit Beam Size
In general, c-arm operators tend to maximize the area of the x-ray beam so they can visualize a large area of tissue. This practice can expose the patient and staff to unnecessary radiation because the size of the beam is proportional to the amount of radiation emitted. Whenever possible, the operator should limit beam size by contracting the lead shutters, or collimators. Because it reduces scatter radiation, collimation improves image quality. Pru-dent use of collimators can also block out bright areas, improving resolution of other tissues.
Maintain Proper Focal Distance
C-arms operate most efficiently at the manufacturer's specified focal distance, and moving the "C" too far in one direction or the other can create unnecessary radiation exposure. Moving the x-ray tube too close to the patient can cause the patient's skin to burn during an extended fluoroscopy procedure. On the other hand, if the operator moves the x-ray tube too far from the patient, the image will magnify and the unit may boost radiation output in an effort to maintain image brightness and quality. As a rule of thumb, increasing focal distance by a factor of two increases radiation exposure by a factor of four. For this reason, the operator should use the magnification mode only when truly necessary.
Eliminate Extraneous Lighting
Extraneous light can interfere with the fluoroscopic image and hinder the eye's ability to resolve detail. When this happens, operators tend to use the magnification mode or take other measures that unnecessarily increase scatter radiation.
Keep Your Guard Up
Scientific consensus groups-including the International Commission on Radiological Protection and NCRP- have recommended lowering the current annual whole body limit of 5 rem per year by a factor of five. Given that the average c-arm emits an average of 2 rem of radiation per minute, it makes sense to practice "ALARA." By following these common-sense safety tips, you can better protect your patients and staff.