A technique for estimating 4D-CBCT using prior knowledge and limited-angle projections

• Published in: Medical physics (Lancaster) Vol. 40; no. 12; pp. 121701 - n/a
• Main Authors: Zhang, You, Yin, Fang-Fang, Segars, W. Paul, Ren, Lei
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01.12.2013
• Subjects: 4D‐CBCT; ACCURACY; Analysis of motion; Biological material, e.g. blood, urine; Haemocytometers; Cancer; cardiology; COMPARATIVE EVALUATIONS; compressed sensing; Computed tomography; Computerised tomographs; computerised tomography; COMPUTERIZED TOMOGRAPHY; Cone beam computed tomography; Cone-Beam Computed Tomography - methods; constrained optimization; DEFORMATION; diagnostic radiography; Digital computing or data processing equipment or methods, specially adapted for specific applications; Dosimetry; Eigenvalues; Four-Dimensional Computed Tomography - methods; free‐form deformation; Humans; Image data processing or generation, in general; image estimation; IMAGE PROCESSING; LIMITING VALUES; lung; Lung Neoplasms - diagnostic imaging; Lung Neoplasms - physiopathology; Lung Neoplasms - radiotherapy; LUNGS; medical image processing; Medical image reconstruction; Medical imaging; minimisation; MINIMIZATION; Models, Biological; motion compensation; Movement; noise; Numerical modeling; Optimization; PATIENTS; PCA motion modeling; PHANTOMS; Phantoms, Imaging; PHASE SHIFT; physiological models; Pneumodyamics, respiration; pneumodynamics; POLAR-CAP ABSORPTION; Principal Component Analysis; radiation therapy; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Radiotherapy, Image-Guided; Therapeutic applications, including brachytherapy; image estimation; 4D-CBCT; PCA motion modeling; free-form deformation; constrained optimization
• ISSN: 0094-2405; 2473-4209; 2473-4209
• DOI: 10.1118/1.4825097

Purpose: To develop a technique to estimate onboard 4D-CBCT using prior information and limited-angle projections for potential 4D target verification of lung radiotherapy. Methods: Each phase of onboard 4D-CBCT is considered as a deformation from one selected phase (prior volume) of the planning 4D-CT. The deformation field maps (DFMs) are solved using a motion modeling and free-form deformation (MM-FD) technique. In the MM-FD technique, the DFMs are estimated using a motion model which is extracted from planning 4D-CT based on principal component analysis (PCA). The motion model parameters are optimized by matching the digitally reconstructed radiographs of the deformed volumes to the limited-angle onboard projections (data fidelity constraint). Afterward, the estimated DFMs are fine-tuned using a FD model based on data fidelity constraint and deformation energy minimization. The 4D digital extended-cardiac-torso phantom was used to evaluate the 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, including changes of respiration amplitude, lesion size and lesion average-position, and phase shift between lesion and body respiratory cycle. The lesions were contoured in both the estimated and “ground-truth” onboard 4D-CBCT for comparison. 3D volume percentage-difference (VPD) and center-of-mass shift (COMS) were calculated to evaluate the estimation accuracy of three techniques: MM-FD, MM-only, and FD-only. Different onboard projection acquisition scenarios and projection noise levels were simulated to investigate their effects on the estimation accuracy. Results: For all simulated patient and projection acquisition scenarios, the mean VPD (±S.D.)/COMS (±S.D.) between lesions in prior images and “ground-truth” onboard images were 136.11% (±42.76%)/15.5 mm (±3.9 mm). Using orthogonal-view 15°-each scan angle, the mean VPD/COMS between the lesion in estimated and “ground-truth” onboard images for MM-only, FD-only, and MM-FD techniques were 60.10% (±27.17%)/4.9 mm (±3.0 mm), 96.07% (±31.48%)/12.1 mm (±3.9 mm) and 11.45% (±9.37%)/1.3 mm (±1.3 mm), respectively. For orthogonal-view 30°-each scan angle, the corresponding results were 59.16% (±26.66%)/4.9 mm (±3.0 mm), 75.98% (±27.21%)/9.9 mm (±4.0 mm), and 5.22% (±2.12%)/0.5 mm (±0.4 mm). For single-view scan angles of 3°, 30°, and 60°, the results for MM-FD technique were 32.77% (±17.87%)/3.2 mm (±2.2 mm), 24.57% (±18.18%)/2.9 mm (±2.0 mm), and 10.48% (±9.50%)/1.1 mm (±1.3 mm), respectively. For projection angular-sampling-intervals of 0.6°, 1.2°, and 2.5° with the orthogonal-view 30°-each scan angle, the MM-FD technique generated similar VPD (maximum deviation 2.91%) and COMS (maximum deviation 0.6 mm), while sparser sampling yielded larger VPD/COMS. With equal number of projections, the estimation results using scattered 360° scan angle were slightly better than those using orthogonal-view 30°-each scan angle. The estimation accuracy of MM-FD technique declined as noise level increased. Conclusions: The MM-FD technique substantially improves the estimation accuracy for onboard 4D-CBCT using prior planning 4D-CT and limited-angle projections, compared to the MM-only and FD-only techniques. It can potentially be used for the inter/intrafractional 4D-localization verification.