Title:
Radiation dose index of renal colic protocol CT studies in the United States: a report from the American College of Radiology National Radiology Data Registry.

Abstract:
To determine radiation dose indexes for computed tomography (CT) performed with renal colic protocols in the United States, including frequency of reduced-dose technique usage and any institutional-level factors associated with high or low dose indexes.
The Dose Imaging Registry (DIR) collects deidentified CT data, including examination type and dose indexes, for CT performed at participating institutions; thus, the DIR portion of the study was exempt from institutional review board approval and was HIPAA compliant. CT dose indexes were examined at the institutional level for CT performed with a renal colic protocol at institutions that contributed at least 10 studies to the registry as of January 2013. Additionally, patients undergoing CT for renal colic at a single institution (with institutional review board approval and informed consent from prospective subjects and waiver of consent from retrospective subjects) were studied to examine individual renal colic CT dose index patterns and explore relationships between patient habitus, demographics, and dose indexes. Descriptive statistics were used to analyze dose indexes, and linear regression and Spearman correlations were used to examine relationships between dose indexes and institutional factors.
There were 49 903 renal colic protocol CT examinations conducted at 93 institutions between May 2011 and January 2013. Mean age ± standard deviation was 49 years ± 18, and 53.9% of patients were female. Institutions contributed a median of 268 (interquartile range, 77-699) CT studies. Overall mean institutional dose-length product (DLP) was 746 mGy ⋅ cm (effective dose, 11.2 mSv), with a range of 307-1497 mGy ⋅ cm (effective dose, 4.6-22.5 mSv) for mean DLPs. Only 2% of studies were conducted with a DLP of 200 mGy ⋅ cm or lower (a "reduced dose") (effective dose, 3 mSv), and only 10% of institutions kept DLP at 400 mGy ⋅ cm (effective dose, 6 mSv) or less in at least 50% of patients.
Reduced-dose renal protocol CT is used infrequently in the United States. Mean dose index is higher than reported previously, and institutional variation is substantial.