Comparative analysis of patient scatter to phantom scatter for computed tomography systems

摘要

Current computed tomography (CT) shielding practices are largely based on calculations of scattered radiation emitted froman acrylic head or body phantom, such as the Computed Tomography Dose Index (CTDI) phantom, or anthropomorphicphantoms of these two anatomical categories. This report considers the difference in scattered air kerma or dose from phantommodels, to actual patient scatter under a variety of clinical scan conditions. Empirical patient scatter measurements recordedat different positions around the gantry, for 3 different CT scanners, resulted in average patient scatter fractions per unit DoseLength Product (DLP: mGy cm) at 1 m from the isocentre of 0.09 ± 0.03 and 0.17 ± 0.04 μGy (mGy cm)?1 for head andbody scans respectively. For the purposes of shielding design and scattered dose estimates to staff it is recommended that asingle standard deviation be applied to these averages in the continued interest of conservatism. These values are reasonablycomparative to the widely published scatter fractions by the National Council of Radiological Protection using the CTDIphantom, and the British Institute of Radiology using head and body anthropomorphic phantoms.