AAPM: C-arm radiation scatter least at head & feet

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PHILADELPHIA—Radiation scatter about the patient during abdominal fluoroscopic procedures is not isotropic, and staff would receive reduced dose if positioned at the head or feet, rather than laterally, according to a study presented July 19 at the annual meeting of the American Association of Physicists in Medicine (AAPM).

Dale Schippers and colleagues from Saint Mary's Health Care in Grand Rapids, Mich., positioned a C-arm fluoroscope to image the abdomen and pelvis of a phantom. Their intent was to determine where the least amount of scattered radiation was and to guide staff in the choice of preferred position.

They performed detailed measurements with the x-ray beam positioned posterior to anterior and with an additional set of measurements performed in the anterior to posterior orientation. Radiation exposure was measured at various distances and angles from the phantom. The mean energy of the scattered radiation was also determined at several locations and C-arm orientations.

Researchers found that the intensity of scattered radiation is a function of both distance and angle of measurement relative to the phantom. The intensity in the long-axis direction of the phantom, even for equal distance from the x-ray field, is significantly less than the intensity at the phantom's side.

The intensity also depends upon the orientation of the x-ray tube, Schippers said. Scattered radiation, measured at the operator's eye level, is approximately five-times greater when the x-ray tube is positioned above the patient versus below the patient.

Schippers and colleagues also found that scattered radiation was less at the image intensifier compared with the x-ray tube.

"Everyone who can should position themselves either closer to the head or the feet," Schippers concluded. "And if possible, it's better to stand by the image intensifier than the x-ray tube."