Effect of table height displacement and patient center deviation on size‑specific dose estimates calculated from computed tomography localizer radiographs

摘要

The aim of this study is to evaluate the effect of table height displacement and patient center deviation along the z-axis on size-specific dose estimate (SSDE) calculations based on computed tomography (CT) localizer radiographs in pediatric and adult abdominal CT examinations. CT localizer radiographs and CT axial images were acquired with table heights of - 5.0, - 2.5, 0.0 (center), 2.5, and 5.0 cm using two acrylic self-made phantoms filled with water. Water-equivalent diameters (Dw) were calculated from the CT localizer radiographs and CT axial images. Relative errors of SSDEs from the CT localizer radiographs to SSDEs from the CT axial images were calculated to evaluate the effect of table height displacement. Furthermore, patient center deviations and indices of SSDE overestimation were measured from the clinical data of 110 abdominal CT examinations. The relative errors of SSDEs in phantoms equivalent to 1-year-old and 20-year-old Japanese reference persons ranged from - 2.45% (table height of 50 mm) to + 1.88% (- 50 mm) and from - 4.22% (50 mm) to + 3.79% (- 50 mm), respectively. The largest center deviation in all patients ranged from - 43.1 to 21.5 mm (median: - 14.4 mm). The indices of SSDE overestimation for all patients ranged from - 16.2 to 6.9 mm (median: - 2.2 mm). We found that the effects of table height displacement and patient center deviation along the z-axis on SSDEs calculated from CT localizer radiographs in pediatric phantoms were smaller compared to adult phantoms. In order to correct these patient center deviations, it is necessary to apply an appropriate correction technique in each section along the z-axis.