Correct Patient Positioning Can Decrease CT Radiation Dose

by Barbara Kram, Editor | March 27, 2007

Centering the patient on the gantry
can reduce radiation exposure
by as much as 56%.

Simply centering the patient appropriately on the CT gantry can reduce radiation dose by as much as 56%, yet nearly all patients are incorrectly positioned for their examinations, a new study shows.

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. Dr. Kalra is one of the authors of the study.

As part of the study, the 63 patients were positioned on the scanner gantry table by a radiology technologist according to standard department protocol. An x-ray was taken to show the initial patient location. The CT scanner's laser guidance system for patient positioning estimated the point where the patient would be centered on the CT gantry. "We then used an automatic centering technique (that isn't commercially available yet) to determine the true center point," Dr. 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.

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

The study appeared in the February issue of the American Journal of Roentgenology, which is published by the American Roentgen Ray Society.

The American Journal of Roentgenology (AJR) is a highly respected peer-reviewed monthly radiology journal published by the American Roentgen Ray Society (ARRS). For almost 100 years, the AJR has been recognized as one of the best specialty journals in the world. The ARRS and AJR are named after Wilhelm Röentgen, who discovered the x-ray in 1895. For more information, visit www.arrs.org.