Feasibility study of a synchronized‐moving‐grid (SMOG) system to improve image quality in cone‐beam computed tomography (CBCT)

Ren, Lei; Yin, Fang‐Fang; Chetty, Indrin J.; Jaffray, David A.; Jin, Jian

doi:10.1118/1.4736826

Cited by 28 publications

(32 citation statements)

References 48 publications

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“…Although several techniques to correct the CBCT scatter artifacts have been proposed, e.g., using collimators, antiscatter grids and blockers, a standard approach remains unclear. [19][20][21][22][23][24] In this study, we investigated the feasibility of using deformable image registration () to create a modified planning CT that closely replicates the CBCT image as a basis of dose calculation for adaptive intensity modulated radiotherapy (IMRT) of the prostate. This method is hypothesized to be feasible due to the emergence of sophisticated  techniques capable of handling multimodal image registration.…”

Section: Introductionmentioning

confidence: 99%

Validation of a deformable image registration technique for cone beam CT‐based dose verification

et al. 2015

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Purpose: As radiation therapy evolves toward more adaptive techniques, image guidance plays an increasingly important role, not only in patient setup but also in monitoring the delivered dose and adapting the treatment to patient changes. This study aimed to validate a method for evaluation of delivered intensity modulated radiotherapy (IMRT) dose based on multimodal deformable image registration () for prostate treatments. Methods: A pelvic phantom was scanned with CT and cone-beam computed tomography (CBCT). Both images were digitally deformed using two realistic patient-based deformation fields. The original CT was then registered to the deformed CBCT resulting in a secondary deformed CT. The registration quality was assessed as the ability of the  method to recover the artificially induced deformations. The primary and secondary deformed CT images as well as vector fields were compared to evaluate the efficacy of the registration method and it's suitability to be used for dose calculation. , a free and open source software was used for deformable image registration. A B-spline algorithm with optimized parameters was used to achieve the best registration quality. Geometric image evaluation was performed through voxel-based Hounsfield unit (HU) and vector field comparison. For dosimetric evaluation, IMRT treatment plans were created and optimized on the original CT image and recomputed on the two warped images to be compared. The dose volume histograms were compared for the warped structures that were identical in both warped images. This procedure was repeated for the phantom with full, half full, and empty bladder. Results: The results indicated mean HU differences of up to 120 between registered and ground-truth deformed CT images. However, when the CBCT intensities were calibrated using a region of interest (ROI)-based calibration curve, these differences were reduced by up to 60%. Similarly, the mean differences in average vector field lengths decreased from 10.1 to 2.5 mm when CBCT was calibrated prior to registration. The results showed no dependence on the level of bladder filling. In comparison with the dose calculated on the primary deformed CT, differences in mean dose averaged over all organs were 0.2% and 3.9% for dose calculated on the secondary deformed CT with and without CBCT calibration, respectively, and 0.5% for dose calculated directly on the calibrated CBCT, for the full-bladder scenario. Gamma analysis for the distance to agreement of 2 mm and 2% of prescribed dose indicated a pass rate of 100% for both cases involving calibrated CBCT and on average 86% without CBCT calibration. Conclusions: Using deformable registration on the planning CT images to evaluate the IMRT dose based on daily CBCTs was found feasible. The proposed method will provide an accurate dose distribution using planning CT and pretreatment CBCT data, avoiding the additional uncertainties introduced by CBCT inhomogeneity and artifacts. This is a necessary initial step toward future imageguided adaptive ...

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Section: Introductionmentioning

confidence: 99%

Validation of a deformable image registration technique for cone beam CT‐based dose verification

et al. 2015

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“…In addition, we noted that the amplitude was unusually small at the starting of a scan (starting at θ = 90° for clockwise, and θ = 290° at counter-clockwise), and quickly increased to normal after several projections. We speculated that this unusual behaviour was due to image lag (19) and would not be further investigated in this study. Fig.…”

Section: Resultsmentioning

confidence: 97%

Correction of Bowtie-Filter Normalization and Crescent Artifacts for a Clinical CBCT System

Zhang

Kong

Huang

et al. 2016

Technol Cancer Res Treat

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Purpose To present our experiences in understanding and minimizing bowtie-filter (BF) crescent artifacts (BCA) and BF normalization artifacts (BNA) in a clinical cone beam computed tomography (CBCT) system. Methods BF position and profile variations during gantry rotation were studied. Two previously proposed strategies (A and B) were applied to the clinical CBCT system to correct BCA. Physical calibration and analytical approaches were used to minimize the norm phantom misalignment and to correct for BNA. A combined procedure to reduce BCA and BNA was proposed and tested on a norm phantom, CatPhan and a patient, and evaluated using standard deviation of Hounsfield-unit (HU) along a sample line. Results The BF exhibited not only a translational shift, but also an amplitude variation in its projection profile during gantry rotation. Strategy B was better than Strategy A slightly in minimizing BCA, possibly because it corrected the amplitude variation, suggesting that the amplitude variation plays a role in BCA. The physical calibration largely reduced the misalignment induced BNA, and the analytical approach further reduced BNA. The combined procedure minimized both BCA and BNA, with HU standard deviation being 63.2, 45.0, 35.0, and 18.8 HU for the best correction approaches of none, BCA, BNA, and BNA+BCA, respectively. The combined procedure also demonstrated reduction of BCA and BNA in a CatPhan and a patient. Conclusions We have developed a step-by-step procedure that can be directly used in clinical CBCT systems to minimize both BCA and BNA.

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“…However, the intensity mismatches between DRRs and real kV/MV projection data caused by imaging artifact, such as scattering, beam hardening, and gray level mismatch due to kV-MV energy differences, can still cause differences within the NCC, which may affect the data fidelity value and optimization of the algorithm. This can be potentially solved using modeling/correction of image artifacts and kV-MV conversion techniques mentioned in previous studies (Yin et al 2005, Ren et al 2012, 2014, 2016). Another option is to explore the feasibility of using mutual information as the similarity matrix, which could be more robust than NCC.…”

Section: Discussionmentioning

confidence: 99%

Reducing scan angle using adaptive prior knowledge for a limited-angle intrafraction verification (LIVE) system for conformal arc radiotherapy

et al. 2017

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The purpose of this study is to develop an adaptive prior knowledge guided image estimation technique to reduce the scan angle needed in the limited-angle intrafraction verification (LIVE) system for 4D-CBCT reconstruction. The LIVE system has been previously developed to reconstruct 4D volumetric images on-the-fly during arc treatment for intrafraction target verification and dose calculation. In this study, we developed an adaptive constrained free-form deformation reconstruction technique in LIVE to further reduce the scanning angle needed to reconstruct the 4D-CBCT images for faster intrafraction verification. This technique uses free form deformation with energy minimization to deform prior images to estimate 4D-CBCT based on kV-MV projections acquired in extremely limited angle (orthogonal 3°) during the treatment. Note that the prior images are adaptively updated using the latest CBCT images reconstructed by LIVE during treatment to utilize the continuity of the respiratory motion. The 4D digital extended-cardiac-torso (XCAT) phantom and a CIRS 008A dynamic thoracic phantom were used to evaluate the effectiveness of this technique. The reconstruction accuracy of the technique was evaluated by calculating both the center-of-mass-shift (COMS) and 3D volume-percentage-difference (VPD) of the tumor in reconstructed images and the true on-board images. The performance of the technique was also assessed with varied breathing signals against scanning angle, lesion size, lesion location, projection sampling interval, and scanning direction. In the XCAT study, using orthogonal-view of 3° kV and portal MV projections, this technique achieved an average tumor COMS/VPD of 0.4 ± 0.1 mm/5.5 ± 2.2%, 0.6 ± 0.3 mm/7.2 ± 2.8%, 0.5 ± 0.2 mm/7.1 ± 2.6%, 0.6 ± 0.2 mm/8.3 ± 2.4%, for baseline drift, amplitude variation, phase shift, and patient breathing signal variation, respectively. In the CIRS phantom study, this technique achieved an average tumor COMS/VPD of 0.7 ± 0.1 mm/7.5 ± 1.3% for a 3 cm lesion and 0.6 ± 0.2 mm/11.4 ± 1.5% for a 2 cm lesion in the baseline drift case. The average tumor COMS/VPD were 0.5 ± 0.2 mm/10.8 ± 1.4%, 0.4 ± 0.3 mm/7.3 ± 2.9%, 0.4 ± 0.2 mm/7.4 ± 2.5%, 0.4 ± 0.2 mm/7.3 ± 2.8% for the four real patient breathing signals, respectively. Results demonstrated that the adaptive prior knowledge guided image estimation technique with LIVE system is robust against scanning angle, lesion size, location and scanning direction. It can estimate on-board images accurately with as little as 6 projections in orthogonal-view 3° angle. In conclusion, adaptive prior knowledge guided image reconstruction technique accurately estimates 4D-CBCT images using extremely-limited angle and projections. This technique greatly improves the efficiency and accuracy of LIVE system for ultrafast 4D intrafraction verification of lung SBRT treatments.

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Feasibility study of a synchronized‐moving‐grid (SMOG) system to improve image quality in cone‐beam computed tomography (CBCT)

Cited by 28 publications

References 48 publications

Validation of a deformable image registration technique for cone beam CT‐based dose verification

Validation of a deformable image registration technique for cone beam CT‐based dose verification

Correction of Bowtie-Filter Normalization and Crescent Artifacts for a Clinical CBCT System

Reducing scan angle using adaptive prior knowledge for a limited-angle intrafraction verification (LIVE) system for conformal arc radiotherapy

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