SU‐E‐J‐50: Does a Breathing Surrogate From a Point On the Abdominal Skin Represent the Organ Motion in Thorax for Phase‐Based 4D CT Sorting?

Abstract

Purpose:This work aims (1) to determine the validity of the current practice of the phase‐based 4DCT sorting (abdomen signal) for thorax scans; (2) to assess the potential benefit of utilizing the 3D surface breathing surrogate of chest area for phase‐based 4DCT sorting.Methods:Dynamic 3D surface images over the chest and abdomen were acquired using 3D‐suface‐camera‐system (VisionRT Ltd., London, UK) for a total of 10 patients. The vertical motions of five regions‐of‐interest (ROIs): abdomen, mid‐sternum, lower‐, middle‐, and upper‐ ipsilateral‐chest were tracked. Based on our previous work, the main source of motion artifact is the variation‐of‐phase‐differences (VPD) between the breathing surrogate and the organ motion during scanning. Thus, we utilize VPD as a quantitative index of the variation of the resulting 4DCT images. The average VPD over a 60 second time‐period was calculated for each of the abdomen and ROI combination. A simulation study with a wire phantom was designed to demonstrate the resulting 4DCT images.Results:Simulation showed significant image distortion or motion artifacts when VPD is larger than 5% of breathing period. The average VPDs of individual ROIs of each patient indicates that 75%, 59% and 22% cases have VPD larger than 5%, 10% and 15% of period each cycle between the selected ROI and the abdominal motions patterns, respectively (10.1±6.0 %, minimum 1.0% to maximum 23.9 %). Overall, patients with less 3‐second breathing‐period present VPD larger than 10%. The correlations between the abdomen and individual chest ROIs motions as well as the motions among chest ROIs are highly case‐dependent.Conclusion:Abdominal motion does not represent the chest motions for some of the patients. This results in motion artifacts in the phase‐based 4DCT. Utilizing the surface surrogate of the chest region can potentially improve phase‐based 4DCT sorting for thorax 4DCT scan, especially for fast breathing patients.