International variation in radiation dose for computed tomography examinations: prospective cohort study

Abstract

Objective: To determine patient, institution, and machine characteristics that contribute to variation in radiation doses used for computed tomography (CT).

Design: Prospective cohort study.

Setting: Data were assembled and analyzed from the University of California San Francisco CT International Dose Registry.

Participants: Standardized data from over 2.0 million CT examinations of adults who underwent CT between November 2015 and August 2017 from 151 institutions, across seven countries (Switzerland, Netherlands, Germany, United Kingdom, United States, Israel, and Japan).

Main outcome measures: Mean effective doses and proportions of high dose examinations for abdomen, chest, combined chest and abdomen, and head CT were determined by patient characteristics (sex, age, and size), type of institution (trauma center, care provision 24 hours per day and seven days per week, academic, private), institutional practice volume, machine factors (manufacturer, model), country, and how scanners were used, before and after adjustment for patient characteristics, using hierarchical linear and logistic regression. High dose examinations were defined as CT scans with doses above the 75th percentile defined during a baseline period.

Results: The mean effective dose and proportion of high dose examinations varied substantially across institutions. The doses varied modestly (10-30%) by type of institution and machine characteristics after adjusting for patient characteristics. By contrast, even after adjusting for patient characteristics, wide variations in radiation doses across countries persisted, with a fourfold range in mean effective dose for abdomen CT examinations (7.0-25.7 mSv) and a 17-fold range in proportion of high dose examinations (4-69%). Similar variation across countries was observed for chest (mean effective dose 1.7-6.4 mSv, proportion of high dose examinations 1-26%) and combined chest and abdomen CT (10.0-37.9 mSv, 2-78%). Doses for head CT varied less (1.4-1.9 mSv, 8-27%). In multivariable models, the dose variation across countries was primarily attributable to institutional decisions regarding technical parameters (that is, how the scanners were used).

Conclusions: CT protocols and radiation doses vary greatly across countries and are primarily attributable to local choices regarding technical parameters, rather than patient, institution, or machine characteristics. These findings suggest that the optimization of doses to a consistent standard should be possible.

Study registration: Clinicaltrials.gov NCT03000751.

Conflict of interest statement

Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: support from the US National Institutes of Health; Patient-Centered Outcomes Research Institute; Centers for Disease Control and Prevention; and the University of California Office of the President, Center for Health Quality and Innovation for the submitted work; RS-B reports grants from the US National Institutes of Health, Patient-Centered Outcomes Research Institute, Centers for Disease Control and Prevention, and the University of California Office of the President, is on a scientific advisory board, and has given talks for Bayer Healthcare; BND is on a scientific advisory board and has given talks for Bayer Healthcare; AJE has served as a consultant to GE Healthcare, and Columbia University has received support for other research from Toshiba America Medical Systems; MD reports grants and personal fees from Bayer Healthcare, grants and personal fees from Siemens Healthcare, grants from Philips Healthcare, personal fees from Cook Medical, outside the submitted work; AS reports non-financial support and is on Bayer Healthcare scientific advisory board; JS has given talks for Bayer Healthcare; JEW reports institutional grants from Agfa, Bard, Bayer, GE, Optimed, Philips, Siemens, personal fees (speaker’s bureau) from Bayer, Siemens, outside the submitted work; DLM is on an advisory board for Hologic; the remaining authors have nothing to disclose.

Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Figures

Fig 1

Distribution in effective radiation dose by institution for abdomen CT, after adjustment for patient characteristics. Each column signifies one institution, ranked by mean effective dose. Light purple columns=5th and 95th percentiles of effective dose; dark purple, pink, and yellow column sections=25th and 75th percentiles of effective dose; lines=medians; horizontal solid line and dashed line=benchmark and target doses for abdomen, defined as the 75th and 50th percentiles of dose for all abdominal scans performed before 30 April 2016

Fig 2

Distribution of effective radiation dose by country and scan region, after adjustment for patient characteristics. Each column signifies one country or the European Union, with one horizontal line denoting each observation within the country. IL=Israel; JP=Japan; pink lines=within 25th and 75th percentiles; orange lines=two standard deviations from the mean; purple lines=outliers; horizontal solid line and dashed line=benchmark and target doses for each anatomical area, defined as the 75th and 50th percentiles of dose for all scans of that type performed before 30 April 2016

Fig 3

Mean effective radiation dose by machine in abdomen computed tomography (CT) scans, with different levels of adjustment. Model 1=unadjusted results; subsequent adjustments included: model 2, patient characteristics; model 3, institutional characteristics; model 4, machine manufacturer; model 5, machine model; and model 6, technical parameters. Rows=mean relative effective dose and 95th percentile of relative dose for two randomly chosen machines, with mean dose by country at the corresponding level of adjustment within multivariable model. Lines=dose for single machines. For abdomen examinations in model 1, 95th percentile of relative dose was 2.65 and mean effective dose ranged from 7.3 mSv (Switzerland) to 15.7 mSv (Israel)