Radiation Doses for Identical CTs Lower, but Still Variable

April 5, 2017

Radiation doses for identical CT scans are still variable, despite lower levels overall.

Computed tomography (CT) scan radiation doses are dropping, but they remain variable even for identical examinations, according to a study published in the American Journal of Roentgenology. Researchers from the United States and Switzerland sought to determine the radiation doses used among adult patients undergoing clinically indicated, repeat identical thoracoabdominal CT examinations. The researchers obtained radiation dose data from 2,851 subjects who underwent 12,635 repeat identical CT scans in one health system. There were a mean of 4.8 scans per patient. The CT protocols included in the study were: • Chest-abdomen-pelvis with contrast administration (4,621 CT studies of 1,064 patients); Abdomen-pelvis with contrast administration (876 CT studies of 261 patients);• Renal stone (1,053 CT studies of 380 patients); and • Chest without contrast (6,085 CT studies of 1,146 patients).  The results showed a trend was observed toward global reduction in size-specific dose estimate  (SSDE) values with all protocols investigated: • Chest-abdomen-pelvis slope, −1.78; • Abdomen-pelvis slope, −0.82; • Renal stone slope, −0.83; and• Chest slope, −0.47. The intraindividual analyses of radiation dose distribution showed widespread variability in SSDE values across the four protocols investigated: • Chest-abdomen-pelvis mean coefficient of variance, 14.02 mGy; • Abdomen-pelvis mean coefficient of variance, 10.26 mGy; • Renal stone mean coefficient of variance, 34.18 mGy; and• Chest mean coefficient of variance, 6.74 mGy. “Although there is a trend toward global reduction in radiation doses, this study showed widespread variability in the radiation dose that each patient undergoing identical repeat thoracoabdominal CT protocols absorbs,” the authors concluded. “These data may provide a foundation for the future development of best-practice guidelines for patient-specific radiation dose monitoring.”