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Deformable Registration-Based Image Estimation Method for 4D CBCT Using Region-Based PCA

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W Harris

W Harris*, Y Zhang , F Yin , L Ren , Duke University Medical Center, Durham, NC


TH-CD-303-6 (Thursday, July 16, 2015) 10:00 AM - 12:00 PM Room: 303

Purpose: To investigate the feasibility of using region-based principal component analysis (PCA) for motion modeling to estimate on-board 4D-CBCT using prior information and limited angle projections for potential 4D target verification of lung radiotherapy.

Methods: A technique for lung 4D-CBCT reconstruction has been previously developed using a deformation field map (DFM)-based strategy. In this method, each phase of the 4D-CBCT is generated by deforming a prior CT volume. The DFM is solved by a motion modeling based on global PCA and free-form deformation (MM-FD) technique, using data fidelity constraint and the deformation energy minimization. For this study, a new region-based PCA method was developed to optimize the motion-modeling part of the MM-FD technique in order to estimate target delineation more accurately using fewer on-board projection angles. First, the DFMs are estimated using the region-based PCA divides the motion model extracted from planning 4D-CT into two regions: tumor and everything else. The motion model parameters of both regions are optimized together based on data fidelity constraint with relative weighting added to the tumor PCA model. The 4D digital extended cardiac-torso phantom was used to evaluate the region-based PCA MM-FD technique. A lung patient with a 30 mm diameter lesion was simulated with various anatomical and respirational changes from planning 4D CT to onboard volume. The reconstruction accuracy was evaluated by the Volume-Percent-Difference(VPD)/Center-of-Mass-Shift(COMS) between lesions in the estimated and “ground-truth” on board 4D CBCT

Results: For patient scenarios with various shifts of tumor from planning CT to on-board acquisition with 15 degree orthogonal projections, the average VPD/COMS for the MM-FD technique was 5.04%/0.26 mm and 23.23%/2.4mm for region-based and global PCA MM-FD, respectively.

Conclusion: The region-based PCA MM-FD technique can potentially further reduces the scan angle needed for onboard 4D CBCT reconstruction for ultra-fast 4D verification.

Funding Support, Disclosures, and Conflict of Interest: National Institutes of Health Grant No. R01-CA184173 Varian Medical System

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