Targeted CT Dose Reduction Using a Novel Dose Metric and the American College of Radiology Dose Index Registry: Application to Thoracic CT Angiography.

OBJECTIVE: The purpose of this article is to illustrate the use of the American College of Radiology Dose Index Registry data with a novel measurement of exposure to guide quality improvement efforts. MATERIALS AND METHODS: Using information from the Dose Index Registry report covering July through December 2012, we examined our relative ranking compared with the national median CT dose for the 20 most frequently performed examinations at our institution. The total exposure variance, defined as the difference between institutional and median national dose multiplied by the local examination frequency and expressed in units of mGy-persons, was calculated. Using this metric, two examinations were selected for investigation: pulmonary and thoracic CT angiography (CTA). Protocol modifications were implemented, and postintervention dose data were assessed from the report 1 year later. RESULTS: As indicated by size-specific dose estimates (SSDEs), the 2012 pulmonary CTA was within the national interquartile range; however, total exposure variance analysis showed that it presented the greatest opportunity for improvement on a population basis. Thoracic CTA was a top quartile examination and offered the second highest potential savings. After protocol modification, the average pulmonary CTA SSDEs decreased by 16%, for a population exposure savings of 1776 mGy-persons in the 2013 report. Average thoracic CTA SSDEs decreased by 44%, for a population exposure savings of 1050 mGy-persons. CONCLUSION: Total exposure variance analysis can increase the usefulness of Dose Index Registry data by relating per-examination dose differences to the local examination frequency. This study exhibited reduction of dose metrics for two commonly performed examinations.