Size specific dose estimates and effective dose in multiphase abdomen-pelvis CT examinations

This study estimated the size-specific dose estimates (SSDE) in different scan phases and inter-phase variations of multi-phase abdomen-pelvis CT examinations. Various methods employed for determination of SSDE, which takes into account the size of the patient, were compared for 51 multiphase abdomen-pelvis CT examinations using custom written software. These methods are based on effective diameter, water equivalent diameter derived from region of interest and segmentation techniques, diameter of central image and whole scan series. Significant variation was observed in SSDE of pre-contrast phase in comparison to other phases. The effective dose was also estimated and correlated with SSDE. The results indicate that the underestimation in the dose estimated using the machine parameter, CTDI_vol, was in the range of 10%–60% when compared with SSDE. This study concludes that the average SSDE of the whole examination is a better representation of patient dose in the case of multi-phase examinations. It highlights the need for integration of SSDE calculating software in the CT scanner systems for accurate estimation of patient doses.