The Impact of Novel X-Ray Systems and X-Ray System Optimization on Patient Radiation Dose Administered During Cardiac Catheterization

Abstract: Introduction. The effect of x-ray system optimization on patient radiation dose has received limited study. Methods. We analyzed patient radiation dose in 1786 cardiac catheterization procedures (diagnostic coronary angiography and/or percutaneous coronary intervention [PCI]) performed at a single tertiary-care center before and after x-ray system optimization. Results. After optimization, cineangiography dose-area product (DAP) dose was lower in the overall group of patients who underwent diagnostic angiography and/or PCI (1347 μGy•m² [IQR, 645-2345 μGy•m²] vs 1658 μGy•m² [IQR, 640-2757 μGy•m²]; P=.03), as well as in the diagnostic angiography group (1795 μGy•m² [IQR, 1140-2994 μGy•m²] vs 2356 μGy•m² [IQR, 311-3576 μGy•m²]; P<.01) and PCI group (2152 μGy•m² [IQR, 1338-3477 μGy•m²] vs 2562 μGy•m² [IQR, 1681-3859 μGy•m²]; P=.02). Cineangiography DAP per exposure was also lower in the overall group (143 μGy•m² [IQR, 91-212 μGy•m²] vs 164 μGy•m² [IQR, 106-233 μGy•m²] per exposure; P<.01) and in the diagnostic angiography group (158 μGy•m² [IQR, 102-225 μGy•m²] vs 184 μGy•m² [IQR, 125-271 μGy•m²] per exposure; P<.01). After optimization, cineangiography air kerma (AK) dose (319 mGy [IQR, 197-531 mGy] vs 421 mGy [IQR, 241-600 mGy]; P=.01) and cineangiography AK per exposure (20.7 mGy [IQR, 12.9-29.0 mGy] vs 23.6 mGy [IQR, 14.1-32.9 mGy] per exposure; P=.03) were also lower in the PCI group. There was no significant change in fluoroscopy AK dose after optimization (20.7 mGy [IQR, 12.7-30.1 mGy] vs 20.4 mGy [IQR, 12.8-31.3 mGy] per minute; P=.71) and fluoroscopy DAP dose (156 μGy•m² [IQR, 101-242 μGy•m²] vs 156 μGy•m² [IQR, 102-236 μGy•m²] per minute; P=.91). Conclusion. X-ray system optimization was associated with lower cineangiography DAP, but similar fluoroscopy radiation dose.

J INVASIVE CARDIOL 2020;32(6):218-221. Epub 2020 May 9.

Key words: x-ray system optimization, fluoroscopy, radiation

Although necessary for cardiac catheterization, radiation exposes both patients and operators to both deterministic and stochastic risks, such as skin injury, cataracts,¹ and cancer;^2,3 hence, decreasing radiation dose to “as low as reasonably achievable” (ALARA) is critically important. Reducing radiation dose can be achieved in many ways,⁴ such as not using x-ray unless absolutely necessary, optimal positioning of the patient in relation to the x-ray tube and the image receptor, use of newer x-ray system shielding,^5-7 and real-time radiation monitoring.⁸ 

X-ray system optimization could also reduce patient (and operator) radiation dose, but has received limited study.⁹ We retrospectively examined the impact of x-ray system optimization at a tertiary-care center.

Methods

Patient population and data collection. We retrospectively analyzed patient radiation dose in 1786 cardiac catheterization procedures (mainly diagnostic angiography or percutaneous coronary intervention [PCI]) performed in two cardiac catheterization suites between October 3, 2017 and December 31, 2018 at Abbott Northwestern Hospital, Minneapolis, Minnesota.  The x-ray systems were Artis Q.zen and Artis zee (Siemens Healthcare GmbH). Data collection was performed retrospectively. Study data were collected and managed using REDCap electronic data capture tools hosted at Minneapolis Heart Institute Foundation. REDCap (Research Electronic Data Capture) is a secure, web-based software platform designed to support data capture for research studies, providing: (1) an intuitive interface for validated data capture; (2) audit trails for tracking data manipulation and export procedures; (3) automated export procedures for seamless data downloads to common statistical packages; and (4) procedures for data integration and interoperability with external sources.^10,11 The study was approved by the local institutional review board. 

Definitions. Air-kerma (AK) dose was defined as the procedural cumulative x-ray energy delivered to air at the interventional reference point (ie, 15 cm on the x-ray tube side of the isocenter), the point at which the primary x-ray beam intersects with the rotational axis of the c-arm gantry. Kerma stands for kinetic energy released in matter. Deterministic radiation effects, such as radiation skin injury, correlate directly with the AK dose (measured in mGy) to a particular area. Dose-area product (DAP) was defined as the absorbed dose multiplied by the area irradiated and is expressed as μGy•m². X-ray system optimization was performed on March 4, 2018 by changing cine angiography dose from 170 nGy/pulse to 140 nGy/pulse. Fluoroscopy was defaulted to 5 R curves at 7.5 or 6 frames/s (whereas the default was 10 R curves at 10 and 15 frames/s before the optimization). Acquisition was defaulted to 14 µGy/frame at 10 frames/s (whereas it was previously 24 µGy/frame at 15 frames/s before the optimization). 

Statistical analysis. Continuous variables were presented as median (interquartile range [IQR], defined as 25^th percentile to 75^th percentile) and compared using the Wilcoxon rank-sum test. Two-sided P-values of ≥.05 were considered statistically significant. Statistical analyses were performed with JMP, version 13.0 (SAS Institute). 

Results

All procedures (including diagnostic angiography and PCI). Of the 1786 procedures analyzed, a total of 283 were performed before x-ray system optimization and 1503 were performed afterward. A total of 761 procedures were diagnostic coronary angiographies and 712 were PCIs; the remaining 312 procedures included catheterization for reasons other than angiography or PCI. Compared with prior to optimization, post-optimization cineangiography DAP dose was significantly lower (1658 μGy•m² [IQR, 640-2757 μGy•m²] vs 1347 μGy•m² [IQR, 645-2345 μGy•m²]; P=.03), as was cine DAP per exposure (164 μGy•m² [IQR, 106-233 μGy•m²] vs 143 μGy•m² [IQR, 91-212 μGy•m²]; P<.01) and cine AK per exposure (24.2 mGy [IQR, 14.0-33.0 mGy] vs 21.6 mGy [IQR, 13.3-30.8 mGy]; P=.02) (Table 1, Figures 1 and 2). AK radiation dose was not significantly different before and after optimization.

Diagnostic coronary angiography. Of the 761 coronary angiographies, a total of 124 were performed before and 637 were performed after optimization. After optimization, total DAP dose decreased (1795 μGy•m² [IQR, 1140-2994 μGy•m²] vs 2356 μGy•m² [IQR, 1311-3576 μGy•m²]; P<.01, as did cine DAP (1190 μGy•m² [IQR, 735-1786 μGy•m²] vs 1537 μGy•m² [IQR, 919-2219 μGy•m²]; P<.001) and cine DAP per exposure (158 μGy•m² [IQR, 102-225 μGy•m²] vs 184 μGy•m² [IQR, 125-271 μGy•m²]; P<.01) (Table 2).

PCI. Of the 713 PCIs analyzed, a total of 107 were performed before and 606 were performed after optimization. After optimization, cine DAP was significantly lower (2152 μGy•m² [IQR, 1338-3477 μGy•m²] vs 2562 μGy•m² [IQR, 1681-3859 μGy•m²]; P=.02), as was cine AK (319 mGy [IQR, 197-531 mGy] vs 421 mGy [IQR, 241-600 mGy]; P=.01) and cine AK per exposure (20.7 mGy [IQR, 12.9-29.0 mGy] vs 23.6 mGy [IQR, 14.1-32.9 mGy]; P=.03) (Table 3). 

Discussion

The main finding of our study is that x-ray system optimization was associated with lower cineangiography DAP dose in the overall group of patients (13% reduction), as well as in the subgroups of diagnostic angiography (14% reduction) and PCI (16% reduction). Furthermore, optimization resulted in lower cineangiography AK and AK per exposure dose in the PCI group (24% and 12%, respectively).

X-ray system optimization is simple to perform and does not require additional expenses. Reducing the default radiation doses reduces overall patient radiation dose, and as a result, operator radiation dose. This benefit is achieved in addition to any radiation dose reduction achieved with reducing the fluoroscopy frames/s (7.5 or 6 frames/s were used in all laboratories). Furthermore, x-ray optimization did not result in significantly different fluoroscopy times, as image quality was not lessened to the point that additional fluoroscopy would be needed to overcome this issue. 

Our study adds to prior studies demonstrating that x-ray system optimization results in lower patient radiation dose.^9,12,13 However, each study used a different optimization protocol and included different procedures. For example, the study by Badawy et al¹² excluded PCIs. Their optimization protocol resulted in a statistically significant radiation dose reduction (AK radiation dose: 0.68 mGy [IQR, 0.47-0.95 mGy] vs 0.3 mGy [IQR, 0.2-0.38 mGy], P<.001; DAP radiation dose: 60.2 Gy•cm² [IQR, 43-84.6 Gy•cm²] vs 28 Gy•cm² [IQR, 17.6-35.2 Gy•cm²], P<.001). Similar to our study, there were no concerns regarding image quality. They initiated their study with a radiation awareness week, which could have potentially affected the results. Jurado-Roman et al¹³ demonstrated a 57% reduction in DAP radiation dose, without any reduction in image quality or complexity of procedures.

Apart from x-ray system optimization, another effective and easily implemented strategy to reduce radiation dose is real-time radiation monitoring. It has been demonstrated that real-time monitoring and visualization of peak skin dose is associated with reduced radiation dose during PCI.¹⁴ 

Study limitations. First, this is an observational, retrospective study with all inherent limitations. Second, patient characteristics that might influence radiation dose, not only for the patient but also for the operator, such as body mass index,¹⁵ were not reported. Third, procedure complexity was not taken into consideration. Fourth, the two groups that we compared were not balanced numerically. Finally, we did not evaluate angiographic image quality before and after optimization; however, there were no operator concerns about image quality. 

Conclusion

X-ray system optimization is easy to perform and is associated with significantly lower patient cineangiography DAP dose.

From the Minneapolis Heart Institute and Minneapolis Heart Institute Foundation, Center for Coronary Artery Disease, Minneapolis, Minnesota.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Brilakis reports consulting/speaker honoraria from Abbott Vascular, American Heart Association (associate editor, Circulation), Biotronik, Boston Scientific, Cardiovascular Innovations Foundation (Board of Directors), CSI, Elsevier, GE Healthcare, InfraRedx, Medtronic, Siemens, and Teleflex; research support from Regeneron and Siemens; shareholder, MHI Ventures; Board of Trustees, Society of Cardiovascular Angiography and Interventions. Dr Gössl reports personal fees from Abbott Vascular. Dr Sorajja reports research grants, consulting, and speaking fees from Edwards Lifesciences, Boston Scientific, Medtronic, and Abbott Vascular. Dr Burke reports speaking fees from Opsens Medical; shareholder in Egg Medical and MHI Ventures. The remaining authors report no conflicts of interest regarding the content herein. 

Manuscript submitted November 26, 2019, final version accepted December 4, 2019.

Address for correspondence: Emmanouil S. Brilakis, MD, PhD, Minneapolis Heart Institute, 920 East 28th Street #300, Minneapolis, MN 55407. Email: esbrilakis@gmail.com

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