Room: AAPM ePoster Library
Purpose: markerless motion tracking methods based on MV imaging can only be applied to radiotherapy with 3D conformal plans. The biggest challenge when applying MV imaging for monitoring spine motion in stereotactic body radiosurgery (SBRT) is the small beam apertures due to strong beam modulations in IMRT planning. The purpose of this study is to investigate the feasibility of a markerless motion tracking in spine SBRT delivery using a novel enhanced synthetic treatment beam (ESTB) imaging technique.
Methods: Three clinical spine SBRT plans using 6FFF beam and sliding window IMRT technique were transferred to a spine phantom and delivered on a True Beam machine. Before the delivery, the phantom was aligned to the planning CT using a setup CBCT image, and then an intentional 2 mm lateral shift was made to the couch. During beam delivery, MV images were continuously taken with EPID and automatically grabbed by Varian iTools Capture software with a frame rate of 11.6 fp/s. After preprocessing for scatter correction and beam intensity compensation, every 30 frame MV images, which accounts for 2.6s, were combined to generate an ESTB image for each beam angle. The ESTB images were registered to the CBCT projections at the matched beam angle, based on maximum mutual information (MI) to detect the motion.
Results: to the snapshot MV images, the ESTB images significantly improved the image quality and enlarged the field of view, leading to more reliable and robust image registration. Based on the MI-based rigid registration, our method showed average tracking error of less than 0.4mm in this phantom study.
Conclusion: results in the phantom study suggested that ESTB images from a static IMRT sliding window plan could be used to detect motion of spine, with a high degree of precision of sub-millimeter in planes perpendicular to the beams.
Funding Support, Disclosures, and Conflict of Interest: Memorial Sloan Kettering Cancer Center has a research agreement with Varian Medical Systems
Not Applicable / None Entered.