A, Dashed horizontal line indicates 4-mSv low-dose protocol. B, Mean dose per computed tomographic (CT) scan, measured by volume CT dose index (CTDIvol). Boxes indicate interquartile range, solid circles reflect means, error bars are drawn to the extreme observation within 1.5 times the interquartile range above and below the box, open circles indicate outliers, and horizontal lines in the boxes reflect medians.
Smith-Bindman R, Moghadassi M, Griffey RT, Camargo CA, Bailitz J, Beland M, Miglioretti DL. Computed Tomography Radiation Dose in Patients With Suspected Urolithiasis. JAMA Intern Med. 2015;175(8):1413-1416. doi:10.1001/jamainternmed.2015.2697
Computed tomography (CT) for the evaluation of suspected urolithiasis should use low-dose techniques (<4 mSv)1 given that diagnostic accuracy is equal to or better than that of conventional CT2 and that this technique reduces the risk for radiation-related carcinogenesis. Despite its widespread acceptance, the actual use of low-dose CT for suspected urolithiasis in the United States is unknown. We determined the radiation doses of CT scans for suspected urolithiasis in the emergency department setting.
Data were collected for the Study of Tomography of Nephrolithiasis Evaluation (STONE), a 15-center, randomized comparative-effectiveness trial comparing initial imaging with CT vs ultrasonography in adults with suspected urolithiasis.3,4 The individual institutional review boards of all 15 hospitals approved the study, and written informed consent was obtained from all participants. Patients were eligible if the emergency physician suspected urolithiasis and were excluded if they were obese or at high risk for a significant alternative diagnosis. Demographic and clinical data were collected for all patients from October 1, 2011, through February 28, 2013. Scans with a missing radiation dose (n = 34) were excluded. Distributions of the radiation dose metrics were calculated overall and stratified by patient factors and hospital characteristics (eg, safety net,5 ownership,4 and annual emergency department visit volume). Calculated doses were unadjusted and adjusted for patient factors. We determined the number and proportion of patients who underwent imaging using low-dose techniques within the patient and hospital strata. We used multivariable analysis to determine patient and hospital predictors of dose. Data analysis was performed from February 25, 2014, through April 14, 2015.
A total of 1582 patients with suspected urolithiasis underwent CT during their emergency department visit, and 497 (31.4%) subsequently passed or underwent surgical removal of a stone. Median effective dose was 11 (interquartile range, 7-17; range, 0.34-73) mSv. The median volume CT dose index (CTDIvol), reflecting the mean dose per slice, was 14 (interquartile range, 9-21; range, 0.5-100) mGy (Table). Only 121 patients (7.6%) underwent imaging using low-dose techniques. These results did not change materially when our analysis was limited to patients at high risk for urolithiasis based on a history of stones or results of physician assessment. In the multivariable models, differences in dose by patient age, weight, race, and ethnicity persisted, but we found no differences in dose by the probability of stones or by patient educational level. The median effective dose varied 5-fold across the 15 hospitals from 4 to 19 mSv (P < .001; Figure); this difference persisted after accounting for patient factors. After accounting for random variation by hospital, hospital characteristics were not significantly associated with dose. Radiation dose was unrelated to the sensitivity of imaging for stones.
Less than 8% of patients received appropriately low-dose CT for suspected urolithiasis. Furthermore, we found a 200-fold variation in dose between patients and a 5-fold variation in median dose across hospitals; these differences were not explained by patient or hospital factors. The American College of Radiology Dose Index Registry6 also reports that very few scans labeled as renal colic protocol are conducted using low-dose techniques; however, the Dose Index Registry does not collect the clinical indication for scanning or weight, which could influence scan settings, so the appropriateness of the doses used could not be evaluated. The consistency of our results with those of the Dose Index Registry provides substantial evidence that appropriate low-dose studies are not used widely for the evaluation of suspected urolithiasis.
Our study strengths include the prospective assessment of a large cohort of patients who underwent imaging for the same clinical indication and the detailed collection of clinical data, including dose metrics. However, we do not know how accurately clinical details were communicated to those responsible for deciding how the CT scans should be performed. Most patients in the emergency department with suspected urolithiasis do not undergo scanning with appropriate low-dose techniques, and published recommendations alone are not leading to optimized doses. Our results highlight the urgent need for increased oversight of CT.
Corresponding Author: Rebecca Smith-Bindman, MD, Department of Radiology and Biomedical Imaging, University of California, San Francisco, 350 Parnassus Ave, Room 307, San Francisco, CA 94143 (firstname.lastname@example.org).
Published Online: June 29, 2015. doi:10.1001/jamainternmed.2015.2697.
Author Contributions: Dr Smith-Bindman had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Smith-Bindman, Moghadassi, Griffey, Camargo, Bailitz, Miglioretti.
Acquisition, analysis, or interpretation of data: Smith-Bindman, Moghadassi, Griffey, Bailitz, Beland, Miglioretti.
Drafting of the manuscript: Smith-Bindman, Moghadassi, Griffey.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Moghadassi, Miglioretti.
Obtained funding: Smith-Bindman.
Administrative, technical, or material support: Smith-Bindman, Moghadassi, Griffey, Bailitz, Beland.
Study supervision: Smith-Bindman, Bailitz, Beland.
Conflict of Interest Disclosures: None reported.
Funding/Support: This study was supported by the American Recovery and Reinvestment Act of 2009 through grant R01HS019312 from the Agency for Healthcare Research and Quality (AHRQ) and the National Institutes of Health (NIH), National Cancer Institute K24CA125036-04 Mid-Career Award.
Role of the Funder/Sponsor: The funding source had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Disclaimer: The content of this article is solely the responsibility of the authors and does not necessarily represent the views of the AHRQ or NIH.
Additional Contributions: Alice Fung, MD, Department of Diagnostic Radiology, Oregon Health and Science University, Portland, Brian Murphy, MD, Department of Diagnostic Imaging, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Providence, Jill Corbo, MD, Jacobi Medical Center, Albert Einstein College of Medicine, Bronx, New York, Vickie E. Noble, MD, Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, John Ma, MD, Oregon Health and Science University, Mike Mallin, MD, University of Utah, Salt Lake City, and Ralph Wang, MD, Department of Emergency Medicine, University of California, San Francisco, were all involved in the conduct of the STONE trial and read and provided comments on an earlier version of the manuscript. They were not compensated for this contribution.