Comparison of Water-Equivalent Diameter Measured from CT Localizer Radiograph Based on Two phantoms of the Step-Wedge and Computed Tomography Dose Index

Abstract

The purpose of this study is to compare the water-equivalent diameter (Dw) and size-specific dose estimate (SSDE) obtained from CT localizer radiograph based on the step-wedge and computed tomography dose index (CTDI) phantoms. The two phantoms were scanned using a 64-slice SIEMENS Somatom CT Scanner with tube currents of 100 mA and 120 kV. The CT localizer radiographs of two phantoms were obtained. Subsequently, relationships between pixel values (PV) and water-equivalent thickness (tw) were developed. Based on those relationships, the Dw and SSDE of twenty patients were calculated from the CT localizer radiographs. The results of the Dw and SSDE measured using CT localizer radiographs based on the two phantoms were compared. The relationships between PV and tw obtained from both CT localizer radiographs of the phantoms of step-wedge and CTDI are established. The Dw and SSDE values from the CT localizer radiograph calibrated with the CTDI phantom and step-wedge phantom also have linear relationship with R2 > 0.99. The statistical test value with p-value > 0.05 indicating that the two measurements of Dw and SSDE based on two phantoms are not statistically different. The results from the step-wedge phantom are comparable with those from the CTDI phantom. The relationship PV and tw with CT localizer radiograph from the step-wedge phantom can produce accurate calibration results. The results of the calibration of the step-wedge phantom can then determine the value of Dw and SSDE.