SU‐E‐J‐74: Impact of Respiration‐Correlated Image Quality On Tumor Motion Reconstruction in 4D‐CBCT: A Phantom Study

Abstract

Purpose:To investigate the effects of scanning parameters and respiratory patterns on the image quality for 4‐dimensional cone‐beam computed tomography(4D‐CBCT) imaging, and assess the accuracy of computed tumor trajectory for lung imaging using registration of phased 4D‐CBCT imaging with treatment planning‐CT.Methods:We simulated a periodic and non‐sinusoidal respirations with various breathing periods and amplitudes using a respiratory phantom(Quasar, Modus Medical Devices Inc) to acquire respiration‐correlated 4D‐CBCT images. 4D‐CBCT scans(Elekta Oncology Systems Ltd) were performed with different scanning parameters for collimation size(e.g., small and medium field‐of‐views) and scanning speed(e.g., slow 50°·min−1, fast 100°·min−1). Using a standard CBCT‐QA phantom(Catphan500, The Phantom Laboratory), the image qualities of all phases in 4D‐CBCT were evaluated with contrast‐to‐noise ratio(CNR) for lung tissue and uniformity in each module. Using a respiratory phantom, the target imaging in 4D‐CBCT was compared to 3D‐CBCT target image. The target trajectory from 10‐respiratory phases in 4D‐CBCT was extracted using an automatic image registration and subsequently assessed the accuracy by comparing with actual motion of the target.Results:Image analysis indicated that a short respiration with a small amplitude resulted in superior CNR and uniformity. Smaller variation of CNR and uniformity was present amongst different respiratory phases. The small field‐of‐view with a partial scan using slow scan can improve CNR, but degraded uniformity. Large amplitude of respiration can degrade image quality. RMS of voxel densities in tumor area of 4D‐CBCT images between sinusoidal and non‐sinusoidal motion exhibited no significant difference. The maximum displacement errors of motion trajectories were less than 1.0 mm and 13.5 mm, for sinusoidal and non‐sinusoidal breathings, respectively. The accuracy of motion reconstruction showed good overall agreement with the 4D‐CBCT image quality results only using sinusoidal breathings.Conclusion:This information can be used to determine the appropriate acquisition parameters of 4D‐CBCT imaging for registration accuracy and target trajectory measurements in a clinical setting.