TU-G-141-03: An On-Board 4D-CBCT Reconstruction Technique Using Limited-Angle Projections Based On Motion Modeling and Free-Form Deformation (MM-FD).
PURPOSE: To develop an on-board 4D-CBCT(OB-4D-CBCT) reconstruction technique using prior information and limited-angle projections for 4D inter/intra-fractional target verificationMethods: The OB-4D-CBCT at each phase is considered as a deformation of planning 4D-CT at one selected phase (prior image). The MM-FD technique solves the deformation field maps(DFMs) with a two-step approach: 1. MM: a principal component analysis-based method is applied to the planning 4D-CT to extract a motion model. Coarse estimation of DFMs are obtained by optimizing motion model parameters to meet data-fidelity constraint for limited-angle on-board projections. 2. FD: the coarse DFMs are further fine-tuned by free-form deformation based on data-fidelity constraint and deformation-energy minimization, using constrained-optimization algorithm ASD-POCS. OB-4D-CBCT is then reconstructed by deforming prior volume based on final DFMs. The 4D Digital Extended-cardiac-torso(XCAT) Phantom was used to evaluate MM-FD. A lung patient with 3-cm diameter lesion was simulated to have various anatomical and respirational changes from 4D-CT to OB-4D-CBCT including respiration amplitude change, lesion size change, lesion average-position change, and phase shift between lesion and body respiratory cycle. The lesions were contoured in both the reconstructed and 'ground-truth' OB-4D-CBCT for comparison. 3D volume percentage-difference (VD) and center-of-mass shifts(COMS) were calculated for evaluation. The MM-FD technique was compared with MM-only and FD-only techniques. RESULTS: For all patient scenarios, the mean original VD/COMS between prior volume and true OB-4D-CBCT were 137.65%/15.5mm. Using orthogonal-15-degree scan angle, the mean VD/COMS between reconstructed and true OB-4D-CBCT for MM-only, FD-only and MM-FD techniques were 64.67%/4.9mm, 98.80%/12.1mm and 20.90%/1.3mm, respectively. For orthogonal-30-degree scan angle, the corresponding results were 63.87%/4.9mm, 79.92%/9.9mm and 15.23%/0.5mm. For single-view 30-and 60-degree projections, the mean VD/COMS for MM-FD technique were 32.67%/2.9mm and 19.67%/1.1mm, respectively. CONCLUSION: The MM-FD technique substantially improves the reconstruction accuracy for OB-4D-CBCT using limited-angle projections. It can potentially improve the inter/intra-fractional 4D-localization accuracy for lung SBRT. Research partially supported by grant from Varian Medical Systems.
Zhang, Y; Segars, P; Yin, F; Ren, L
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