SU‐F‐J‐117: Impact of Motion Artifacts On Image Quality and Accuracy of Tumor Motion Reconstruction in 4D CT‐On‐Rails and MV‐CBCT Scans: A Phantom Study

Abstract

Purpose:To compare and quantify respiratory motion artifacts in images from free breathing 4D‐CT‐on‐Rails(CTOR) and those from MV‐Cone‐beam‐CT(MVCB) and facilitate respiratory motion guided radiation therapy.Methods:4D‐CTOR: Siemens Somatom CT‐on‐Rails system with Anzai belt loaded with pressure sensor load cells. 4D scans were performed in helical mode, pitch 0.1, gantry rotation time 0.5s, 1.5mm slice thickness, 120kVp, 400 mAs. Normal and fast breathing (>12rpm) scanning protocols were investigated. Helical scan, AIP(average intensity projection) and MIP(maximum intensity projection) were generated from 4D‐CTOR scans with amplitude sorting into 10 phases.MVCB: Siemens Artiste diamond view(1MV)MVCB was performed with 5MU thorax protocol with 60 second of full rotation.Phantom: Anzai AZ‐733V respiratory phantom. The settings were set to normal and resp. modes with repetition rates at 15 rpm and 10 rpm. Surgical clips, acrylic, wooden, rubber and lung density, total six mock‐ups were scanned and compared in this study.Signal‐to‐noise ratio(SNR), contrast‐to‐noise ratio(CNR) and reconstructed motion volume were compared to different respiratory setups for the mock‐ups.Results:Reconstructed motion volume was compared to the real object volume for the six test mock‐ups. It shows that free breathing helical in all instances underestimates the object excursions largest to −67.4% and least −6.3%. Under normal breathing settings, MIP can predict very precise motion volume with minimum 0.4% and largest −13.9%. MVCB shows underestimate of the motion volume with −1.11% minimum and −18.0% maximum. With fast breathing, AIP provides bad representation of the object motion; however, the MIP can predict the motion volume with −2.0% to −11.4% underestimate.Conclusion:Respiratory motion guided radiation therapy requires good motion recording. This study shows that regular CTOR helical scans provides bad guidance, 4D CTOR AIP cannot represent the fast breathing pattern, MIP can represent the best motion volume, MVCBCT can only be used for normal breathing with acceptable uncertainties.