CT Radiation Dose Should Be Adjusted to Patient Size

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CT Radiation Dose Should Be Adjusted to Patient Size
Nov. 22, 2002 — It's time to adjust the radiation dose of computed tomography (CT) scanners to the patient's weight and abdominal size, according to the results of a prospective study published in the November issue of the American Journal of Roentgenology.

"It used to be, with conventional plain film examinations, that the radiation dose was adjusted depending on the patient's size to avoid overexposing or underexposing the film," author Sanjay Saini, MD, from Massachusetts General Hospital in Boston, says in a news release. "The exposure problem doesn't happen with CT so doses gradually increased because higher doses meant a less grainy image. With the dramatic increase in the use of CT, we've become more concerned about dose levels."

Dr. Saini's group performed diagnostic, contrast-enhanced multidetector CT scanning in 39 patients who were aged at least 65 years and who had a history of cancer. In a blinded review of image quality and anatomic details of the abdominal wall and organs, two radiologists rated randomized CT scan slices done at a standard radiation dose (240-300 mA) and at a 50% reduced dose (120-150 mA) at a constant kilovoltage of 140.

Although the image quality score was significantly higher overall ( P<.005) on the scans obtained with standard-dose CT, there was no statistically significant difference in image quality in the half-dose and standard-dose CT scans in patients who weighed less than 180 pounds and who had a transverse abdominal diameter of less than 34.5 cm, an anteroposterior diameter of less than 28 cm, a cross-sectional circumference of less than 105 cm (42 in), and a cross-sectional area of less than 800 cm .

"Abdominal CT scan quality appears to be acceptable even with a 50% reduction in radiation dose except in patients with large anthropometric measurements," the authors write. "A reduction in CT radiation dose is possible if the tube current is optimized for the patient's weight and abdominal dimensions."

GE Medical Systems helped fund this study. According to Dr. Saini, manufacturers are planning to introduce CT scanners in which the radiation dose changes depending on the density of the body part being imaged.

Am J Roentgenol. 2002;179:1101-1106

Reviewed by Gary D. Vogin, MD

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