TRIPLE THREAT Time, distance and shielding are the 3 basic guides for safety when using X-ray.

Every fluoroscopically guided procedure carries the potential of high radiation exposure for patients and staff. This risk is partially reduced by better understanding how C-arms work and how some simple safety practices can help shield individuals in the OR from harm. Our facility developed safe habits for C-arm use based on the following principles.

1. Mind the distance
Radiation is produced by X-ray tubes that direct beams of energized, high-speed electrons at a target. The force with which the electrons strike the target depends on the accelerating voltage (measured in kVps). Keep beams collimated and the X-ray field size reduced as much as possible.

The most common operator error when using a C-arm is placing the X-ray tube too close to the patient's skin. Moving the tube housing closer to the patient will exponentially increase the skin dose. It will also result in a blurry image, which will require you to take another X-ray picture. The largest amount of scatter radiation is produced where the X-ray beam enters the patient, so by placing the X-ray tube under the patient, not above, you decrease the amount that reaches the C-arm operator's upper body.

2. Adjust radiation output
Many of the newer C-arms let you boost the fluoroscopy output for larger patients. These units can also pulse the beam on and off several times per second, cutting down the patient dose. Newer image processors handle the flicker from a low frame rate as well, maintaining image quality. All newer units have a "last image hold" feature that keeps the last image on the screen even after the beam is turned off, letting physicians inspect the image without keeping the radiation beam on.

The "low-dose" feature can decrease the amount of radiation delivered to the patient and scattered to the personnel in the room. The tradeoff is that the image may have more noise, but for cases in which tissue is being visualized with the use of contrast, such as pain management procedures, the lower radiation delivery to the patient and scatter to personnel is worth it.

MANAGING THE FIELD

6 Keys to Limiting Radiation Scatter

1. Tighten the collimators to irradiate only the tissue of interest, which reduces the patient's total entrance skin exposure, improves image contrast and decreases scatter radiation to the operator.
2. Use image magnification only when necessary. Magnification increases radiation dosage to the selected area. If your C-arm offers selectable kV and automatic exposure control, raise the beam's kVp to improve X-ray penetrability and lower the patient dose at the expense of only a small loss in image contrast.
3. Avoid directing the beam through the patient at an oblique angle. Oblique images are typically associated with increased radiation exposure, because the X-rays are traveling through more tissue and a longer distance. If you do need to use an oblique angle, tilt the image intensifier toward yourself so your legs and feet will receive more exposure than your head and neck.
4. When using fluoroscopy across a patient, position yourself on the same side of the patient as the image intensifier, not the X-ray tube.
5. Vary the entry point of the radiation beam, when practical, to spread the radiation over more skin area and reduce the likelihood that any one spot will be overexposed.
6. Shield the patient's thyroid, eyes and genitals to prevent radiation exposure to these sensitive areas.

— Lori Bailey, RN, BSN,
and Carol Cappella, RN, MSN, CNOR

SMALL DOSES

Recommended Exposure Limits

?	MPD*	ALARA'
?	(mrem / year)
Whole body	5,000	500
(head, trunk, arms above elbows, legs above knees)
Extremities	50,000	5,000
(arms below elbows, legs below knees)
Individual organs, skin	50,000	5,000
Lens of the eye	15,000	1,500
*MPD = maximum permissible dose
'ALARA = as low as reasonably achievable
Source: Adapted from the National Council on Radiation Protection and Measurement's recommendations

3. Wear protection
The absorbed radiation dose to staff in the procedure room is directly proportional to the dose the patient receives. At 1m, a physician will absorb about 0.1% of the patient dose due to scatter, and a smaller additional contribution due to leakage through the side of the tube housing. The maximum allowed effective dose equivalent to the physician's body is 5000mrem per year (natural background radiation amounts to about 300mrem annually).

The 0.5mm lead-equivalent aprons used by physicians during fluoroscopy attenuate 95% of the scattered radiation to the shielded torso, compared with 80% for the lightweight 0.25mm aprons. Hang aprons when storing them to prevent degradation. Leaded thyroid shields and eyeglasses provide additional, but not as comprehensive, protection. Wear leaded gloves if you put your hands near the beam. Use screens suspended from the ceiling, lateral shields and table curtains when operating the C-arm, as these protect from more than 90% of the scattered radiation that occurs during fluoroscopy.

Finally, all personnel in the room during procedures should wear dosimeters (film badges) over leaded aprons or other protective shields so that doses delivered to unprotected body parts can be measured and recorded.

4. Track exposures
Radiation-induced injuries from fluoroscopy are generally not immediately apparent. Other than the mildest symptoms, such as transient erythema, effects of radiation may not appear until weeks after exposure. Early transient erythema occurs after exposure to as little as 200rems of radiation. It appears in several hours, peaks at about 24 hours, and fades in several days. It's uncommon to see records of high doses in an outpatient facility, but pain management patients can exceed 2000mrem per year if their procedures are done regularly. The main concern when dealing with radiation exposure involves the physicians and staff who regularly use fluoroscopy equipment. Track dose rates for all staff members involved with fluoroscopy to ensure higher exposures and serious injuries do not occur (see "Recommended Exposure Limits").

Less is more
Provide staff who regularly work around C-arms with yearly in-services and education about the dangers of radiation exposure. Dosimeters worn by personnel need to be checked quarterly to ensure exposure dosages have not been exceeded. Because radiation can cause damage to the human body, you must try to achieve quality images with the smallest possible radiation dose.