A comparison of radiation dose measured in CT dosimetry phantoms with calculations using EGS4 and voxel-based computational models

CT is a high-dose examination and possibly the dominant contributor to dose from diagnostic radiology. Estimates of organ doses are obtained from Monte Carlo calculations and used to quantify radiation risk. To ensure the validity of using Monte Carlo calculations to estimate actual dose, measurements must be compared with calculations. We have measured doses to CT head and chest dosimetry phantoms and compared them with Monte Carlo (EGS4) calculated doses in voxel-based computational models of the phantoms. The simulation used an x-ray spectrum calculated from the specified values of the scanner's x-ray tube parameters. The scanner's beam-shaping filter was included in the modelling. Measured and calculated doses to both the head and chest phantoms agreed to within 7%. The inclusion of Rayleigh scattering in the calculations has a significant effect if only one slice is scanned but not if multiple slices are scanned.