Correct patient positioning can decrease CT radiation dose

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Simply centering the patient appropriately on the CT gantry can reduce radiation dose by as much as 56 percent, yet nearly all patients are incorrectly positioned for their examinations, according to a new study in the February issue of the American Journal of Roentgenology.

Nearly all, (42 out of 45) patients undergoing abdominal CT examinations were off-center. All 18 patients in the study undergoing chest CT were off-center too, said Mannudeep Kalra, MD, currently at Massachusetts General Hospital in Boston. Kalra is one of the authors of the study.

As part of the study, the 63 patients were positioned on the scanner gantry table, and an x-ray was taken to show the initial patient location. The CT scanner's laser guidance system estimated the point where the patient would be centered. "We then used an automatic centering technique (that isn't commercially available yet) to determine the true center point," Kalra said. Patients were off-center by anywhere from 5.5 mm to 64 mm for chest CT examinations and 5.5 mm to 56 mm for abdominal CT examinations, he said.

When patients were centered appropriately (i.e. based on the automatic centering technique) radiation dose was reduced anywhere from 7 percent to 29.9 percent in chest CT examinations, Kalra said. Radiation dose was reduced between 5.5 percent and 56 percent for abdominal CT examinations, he said.

"This study emphasizes that radiologists and technologists must pay close attention to patient centering. In addition, vendors are encouraged to develop and assess techniques that aid the technologist in accurate patient centering," Kalra said.

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