Quantitative Image Quality Assessment And Quality Assurance Of Advanced Imaging Systems For IGRT

Date(s) - 07/01/2015
9:00 am - 11:00 am

Soyoung Lee, PhD Candidate


With the advent of advanced treatment techniques, imaging guidance plays crucial roles in the image-guided radiation therapy (IGRT). Two imaging modalities – electronic portal imaging devices (EPIDs) and cone-beam CT (CBCT) – are prominently used to verify patient position during the course of radiation treatment. These imaging systems allow daily online positioning correction and have become essential components in high-precision stereotactic body radiotherapy (SBRT). To achieve consistent positioning accuracy on the sub-millimeter level, the development of rigorous quality assurance (QA) program for these systems must be followed. Unfortunately, the current QA approaches are neither effective nor efficient. Particularly, the effectiveness of the current EPID QA procedure has not been quantitatively demonstrated due to insufficient data collection. Thus the operational reliability of the system cannot be determined. For 4D-CBCT, as an extended form of 3D-CBCT, comprehensive study on the impact of scanning parameters and irregular breathing patterns on its performance does not exist yet. Conventional quantitative imaging metrics such as modulation transfer functions (MTF) and clinical detective quantum efficiency (cDQE) have yet to be applied on this new imaging technique. In this study, we proposed a quantitative method to monitor and predict the imaging behavior of EPIDs. The reliability of the method was demonstrated through data collected during a three-year span. Next, for the clinical implementation of 4D-CBCT, we investigated the impact of scanning parameters and breathing patterns on the image quality and the accuracy of computed tumor trajectory for a commercial 4D-CBCT system. The image quality of 4D-CBCT was thoroughly evaluated using quantitative metrics such as contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), motion blurring ratio (MBR), MTF and cDQE. The root-mean-squared-error (RMSE) analysis was used to quantify the accuracy of target trajectory reconstruction. Finally, the impact of various sorting methods on the image quality of 4D-CBCT was investigated. In summary, this study provides a novel and effective approach for EPID QA. Methodologies for quantitative QA of 4D-CBCT has been proposed and analyzed. The results of this research can optimize the use of these advanced imaging systems in high-precision radiotherapy.