Cardiac-Specific Conversion Factors to Estimate Radiation Effective Dose From Dose-Length Product in Computed Tomography

Sigal Trattner; Sandra Halliburton; Carla M Thompson; Yanping Xu; Anjali Chelliah; Sachin R Jambawalikar; Boyu Peng; M Robert Peters; Jill E Jacobs; Munir Ghesani; James J Jang; Hussein Al-Khalidi; Andrew J Einstein

doi:10.1016/j.jcmg.2017.06.006

Cardiac-Specific Conversion Factors to Estimate Radiation Effective Dose From Dose-Length Product in Computed Tomography

JACC Cardiovasc Imaging. 2018 Jan;11(1):64-74. doi: 10.1016/j.jcmg.2017.06.006. Epub 2017 Aug 16.

Authors

Affiliations

¹ Department of Medicine, Division of Cardiology, Columbia University Medical Center, and New York-Presbyterian Hospital, New York, New York.
² Imaging Institute, Division of Radiology, Cleveland Clinic, Cleveland, Ohio, and Lerner Research Institute, Department of Biomedical Engineering, Cleveland Clinic, Cleveland, Ohio, and Department of Chemical and Biomedical Engineering, Cleveland State University, Cleveland, Ohio, and Philips Healthcare, Cleveland, Ohio.
³ Imaging Institute, Division of Radiology, Cleveland Clinic, and Lerner Research Institute, Department of Biomedical Engineering, Cleveland Clinic, and Department of Chemical and Biomedical Engineering, Cleveland State University, Cleveland, Ohio.
⁴ Radiological Research Accelerator Facility, Center for Radiological Research, Columbia University Medical Center, Irvington, New York.
⁵ Department of Pediatrics, Division of Pediatric Cardiology, New York-Presbyterian Morgan Stanley Children's Hospital, and Columbia University Medical Center, New York, New York.
⁶ Department of Radiology, Columbia University Medical Center, and New York-Presbyterian Hospital, New York, New York.
⁷ Advanced Cardiovascular Imaging, New York, New York.
⁸ Section of Cardiac Imaging, Department of Radiology, New York University School of Medicine, and New York University Langone Medical Center, New York, New York.
⁹ Division of Nuclear Medicine, Department of Radiology, New York University, and New York University Langone Medical Center, New York, New York.
¹⁰ Division of Cardiology, Kaiser Permanente San Jose Medical Center, San Jose, California.
¹¹ Duke Clinical Research Institute, Duke University Medical Center, Durham, North Carolina.
¹² Department of Medicine, Cardiology Division, and Department of Radiology, Columbia University Medical Center, and New York Presbyterian Hospital, New York, New York. Electronic address: andrew.einstein@columbia.edu.

Abstract

Objectives: This study sought to determine updated conversion factors (k-factors) that would enable accurate estimation of radiation effective dose (ED) for coronary computed tomography angiography (CTA) and calcium scoring performed on 12 contemporary scanner models and current clinical cardiac protocols and to compare these methods to the standard chest k-factor of 0.014 mSv·mGy^-1cm^-1.

Background: Accurate estimation of ED from cardiac CT scans is essential to meaningfully compare the benefits and risks of different cardiac imaging strategies and optimize test and protocol selection. Presently, ED from cardiac CT is generally estimated by multiplying a scanner-reported parameter, the dose-length product, by a k-factor which was determined for noncardiac chest CT, using single-slice scanners and a superseded definition of ED.

Methods: Metal-oxide-semiconductor field-effect transistor radiation detectors were positioned in organs of anthropomorphic phantoms, which were scanned using all cardiac protocols, 120 clinical protocols in total, on 12 CT scanners representing the spectrum of scanners from 5 manufacturers (GE, Hitachi, Philips, Siemens, Toshiba). Organ doses were determined for each protocol, and ED was calculated as defined in International Commission on Radiological Protection Publication 103. Effective doses and scanner-reported dose-length products were used to determine k-factors for each scanner model and protocol.

Results: k-Factors averaged 0.026 mSv·mGy^-1cm^-1 (95% confidence interval: 0.0258 to 0.0266) and ranged between 0.020 and 0.035 mSv·mGy^-1cm^-1. The standard chest k-factor underestimates ED by an average of 46%, ranging from 30% to 60%, depending on scanner, mode, and tube potential. Factors were higher for prospective axial versus retrospective helical scan modes, calcium scoring versus coronary CTA, and higher (100 to 120 kV) versus lower (80 kV) tube potential and varied among scanner models (range of average k-factors: 0.0229 to 0.0277 mSv·mGy^-1cm^-1).

Conclusions: Cardiac k-factors for all scanners and protocols are considerably higher than the k-factor currently used to estimate ED of cardiac CT studies, suggesting that radiation doses from cardiac CT have been significantly and systematically underestimated. Using cardiac-specific factors can more accurately inform the benefit-risk calculus of cardiac-imaging strategies.

Keywords: cardiac computed tomography; conversion factors; radiation dose.

Publication types

Comparative Study
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

MeSH terms

Computed Tomography Angiography / instrumentation*
Computer Simulation
Coronary Angiography / instrumentation*
Coronary Artery Disease / diagnostic imaging*
Coronary Vessels / diagnostic imaging*
Equipment Design
Humans
Phantoms, Imaging
Predictive Value of Tests
Radiation Dosage*
Tomography Scanners, X-Ray Computed*
Vascular Calcification / diagnostic imaging*

Grants and funding

R01 HL109711/HL/NHLBI NIH HHS/United States