Comparison of methods to estimate water-equivalent diameter for calculation of patient dose.

Modern CT systems seek to evaluate patient-specific dose by converting the CT dose index generated during a procedure to a size-specific dose estimate using conversion factors that are related to patient attenuation properties. The most accurate way to measure patient attenuation is to evaluate a full-field-of-view reconstruction of the whole scan length and calculating the true water-equivalent diameter (D ) using CT numbers; however, due to time constraints, less accurate methods to estimate D using patient geometry measurements are used more widely. In this study we compared the accuracy of D values calculated from three different methods across 35 sample scans and compared them to the true D .