Impact of a Reduced Tube Voltage on CT Angiography and Radiation Dose. Results of the PROTECTION I Study

Objectives: The aim of this study was to determine the impact of a reduced 100-kV tube voltage on image quality and radiation exposure in a pre-defined subgroup analysis of the international, multicenter radiation dose survey PROTECTION I (Prospective Multicenter Study on RadiaTion Dose Estimates Of Cardiac CT AngIOgraphy I) study. Background: Cardiac computed tomography angiography (CCTA) has become a frequently used diagnostic tool in clinical practice. Despite continually improving CT technology, there remain concerns regarding the associated radiation exposure. A reduced tube voltage of 100 kV has been proposed as an effective means for dose reduction in nonobese patients. Methods: The study assessed the relevant radiation dose parameters as well as quantitative and qualitative diagnostic image quality data in a subgroup of 321 patients (100 kV: 82 patients; 120 kV: 239 patients), who were scanned at study sites that applied a 100-kV tube voltage in at least 1 patient. Diagnostic image quality was assessed by an experienced CCTA investigator with a 4-point score (1: nondiagnostic to 4: excellent image quality). Effective radiation dose was estimated from the dose-length-product of each CCTA study. Results: The use of the 100-kV scan protocol was associated with 53% reduction in CCTA median radiation dose estimates, when compared with the conventional 120-kV scan protocol (p < 0.001). Although image noise significantly increased by 26.3% with 100 kV, signal- as well as contrast-to-noise ratios also increased by 7.9% (p = 0.254) and 10.8% (p = 0.027), respectively. Reduction of tube voltage did not impair diagnostic image quality (median diagnostic score: 3.5 [3.25 to 3.75] vs. 3.5 [3.0 to 3.75] for 100 kV vs. 120 kV; p = 0.22). Conclusions: In this nonrandomized PROTECTION I dose survey, reducing the CCTA tube voltage to 100 kV in nonobese patients is associated with a significant reduction in radiation exposure while maintaining diagnostic image quality. Thus, the 100-kV scan technique should be considered for CCTA dose reduction in adequately selected patients.