Entrance Surface Dose during Three-dimensional Imaging with a Flat-panel Detector Angiography System

Abstract

To measure the entrance surface dose (ESD) during three-dimensional (3D) imaging of a phantom and evaluate a method to estimate ESD with use of dose-area product (DAP) values. The present study used an angiographic unit with a digital flat-panel system for 3D imaging. DAP values and ESDs were evaluated on square phantoms with thicknesses of 12.0, 15.0, 18.0, 21.0, and 25.0 cm with use of 5-second acquisitions. ESDs were measured on the lateral and posterior surfaces of the square phantom. DAP values and ESDs were also evaluated on a human-shaped phantom with various table heights, with ESDs measured on the phantom surfaces on the posterior centerline, right middle axillary line, and their midpoint. The posterior ESDs were 7.3 mGy, 12.1 mGy, 18.8 mGy, 26.9 mGy, and 38.5 mGy for the square phantoms with thicknesses of 12 cm, 15 cm, 18 cm, 21 cm, and 25 cm, respectively. The DAP and the posterior ESDs were correlated (r = 0.998, P < .0001). The regression equation was D = DAP x 0.0014, where D was the posterior ESD (mGy). For the human-shaped phantom, the posterolateral ESD tended to be slightly larger than the posteromedial ESD, with the differences less than 10%. The estimated doses based on this relationship were almost equal to the actual posterolateral doses for each table height. The ESD of a single 3D imaging study was considerably lower than the thresholds for radiation skin injuries. The DAP values are useful to estimate the maximum patient ESD during 3D imaging.