P2484Radiation dose reduction in cardiac CT: results from the prospective multicenter registry on radiation dose estimates of cardiac CT angiography in daily practice in 2017

Background: The radiation exposure reported in cardiac CT studies has raised concerns. In 2007, the international PROTECTION I registry estimated the radiation exposure of cardiac CT angiographies with a median dose-length product (DLP) of 885 mGy*cm. Since then, numerous advances in CT technology as well as scan protocols have been developed for dose reduction, but their efficacy in clinical practice is largely unknown. Purpose: The PROTECTION VI study is a multicenter, prospective, worldwide registry designed to evaluate radiation dose exposure and utilization of dosesaving strategies for contrast-enhanced cardiac CT angiography in daily practice. Methods: 60 study sites from 32 different countries participated and enrolled all patients undergoing cardiac CT during one calendar month in 2017. To date core-lab collected image and scan data of 4500 patients have been analyzed. DLP was the main outcome measure. Linear regression analysis was performed to identify independent predictors associated with dose. Results: The median DLP of 4500 cardiac CT studies was 244 mGy*cm (interquartile range: 148 to 360 mGy*cm), which corresponds to an estimated effective dose of 3.4 mSv (conversion factor k = 0.014 mSv*(mGy*cm)-1). When compared with PROTECTION I, the DLP was reduced by approximately 72% (p<0.001). A >30x variability in median DLP was observed between study sites (range of median DLP: 74 to 2289 mGy*cm). The most frequent indication for cardiac CT was the evaluation of coronary artery disease in 88% of patients. Among patient-related factors, multivariable linear regression analysis identified body weight as the predominant independent predictor for higher radiation dose of coronary CT angiography, whereas the use of low tube voltage and the selection of scan protocols were predominant acquisition-related independent predictors for radiation exposure.