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

Zhang, You; Yin, Fang‐Fang; Segars, W. Paul; Ren, Lei

doi:10.1118/1.4825097

Cited by 83 publications

(156 citation statements)

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“…As the organ displacement around the diaphragm could be 2-3 cm or larger in the superior-inferior (SI) direction, respiratory motion should be fully considered for radiation treatments involving thoracic and upper abdominal cancers that involve lung, stomach, pancreas, and liver. 1 The discrepancy could be especially severe in stereotactic body radiation therapy (SBRT) for lung cancer treatment because the consequence is magnified by its low fraction number (3-5 fractions) and high fractional dose (12)(13)(14)(15)(16)(17)(18) Gy per fraction). However, as in vivo dosimetry is currently not available clinically, dose-response studies are generally based on prescribed or planned dose instead of delivered dose.…”

Section: Introductionmentioning

confidence: 99%

“…This is the first proof-of-concept study of delivered dose assessment for SBRT lung cancer treatment that combines principal component analysis (PCA) approach [11][12][13][14][15][16] for 3D reconstructions at sampled timepoints and the Monte Carlobased Dose Planning Method (DPM) 17 for dose calculation. Although the PCA approach has been validated for tumor localization with the presence of significant respiratory motion, further investigation was needed to investigate the feasibility, accuracy, and potential usefulness of using these 3D images for dose calculation, particularly for patients who breathe differently than they did during acquisition of the 4DCT used for motion modeling.…”

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confidence: 99%

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3D delivered dose assessment using a 4DCT-based motion model

et al. 2015

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Purpose: The purpose of this work is to develop a clinically feasible method of calculating actual delivered dose distributions for patients who have significant respiratory motion during the course of stereotactic body radiation therapy (SBRT). Methods: A novel approach was proposed to calculate the actual delivered dose distribution for SBRT lung treatment. This approach can be specified in three steps. (1) At the treatment planning stage, a patient-specific motion model is created from planning 4DCT data. This model assumes that the displacement vector field (DVF) of any respiratory motion deformation can be described as a linear combination of some basis DVFs. (2) During the treatment procedure, 2D time-varying projection images (either kV or MV projections) are acquired, from which time-varying "fluoroscopic" 3D images of the patient are reconstructed using the motion model. The DVF of each timepoint in the time-varying reconstruction is an optimized linear combination of basis DVFs such that the 2D projection of the 3D volume at this timepoint matches the projection image. (3) 3D dose distribution is computed for each timepoint in the set of 3D reconstructed fluoroscopic images, from which the total effective 3D delivered dose is calculated by accumulating deformed dose distributions. This approach was first validated using two modified digital extended cardio-torso (XCAT) phantoms with lung tumors and different respiratory motions. The estimated doses were compared to the dose that would be calculated for routine 4DCT-based planning and to the actual delivered dose that was calculated using "ground truth" XCAT phantoms at all timepoints. The approach was also tested using one set of patient data, which demonstrated the application of our method in a clinical scenario. Results: For the first XCAT phantom that has a mostly regular breathing pattern, the errors in 95% volume dose (D95) are 0.11% and 0.83%, respectively for 3D fluoroscopic images reconstructed from kV and MV projections compared to the ground truth, which is clinically comparable to 4DCT (0.093%). For the second XCAT phantom that has an irregular breathing pattern, the errors are 0.81% and 1.75% for kV and MV reconstructions, both of which are better than that of 4DCT (4.01%). In the case of real patient, although it is impossible to obtain the actual delivered dose, the dose estimation is clinically reasonable and demonstrates differences between 4DCT and MV reconstruction-based dose estimates. Conclusions: With the availability of kV or MV projection images, the proposed approach is able to assess delivered doses for all respiratory phases during treatment. Compared to the planning dose based on 4DCT, the dose estimation using reconstructed 3D fluoroscopic images was as good as 4DCT for regular respiratory pattern and was a better dose estimation for the irregular respiratory pattern.

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

3D delivered dose assessment using a 4DCT-based motion model

et al. 2015

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“…Compared with these methods, the MM-FD method is proved more robust to the motion pattern/anatomical structure variations between 4D-CT and 4D-CBCT (Ref. 20) and can utilize only limited-angle projections for image estimation.…”

Section: D Comparison With Other Methodsmentioning

confidence: 99%

“…For more details, please refer to our previous publications. 20,21,29,30 To comprehensively evaluate the MM-FD estimated images for on-board dose verification, studies were performed using a digital human phantom [extended-cardiac-torso (XCAT) [31][32][33] ] and an anthropomorphic physical phantom ( 008A, Computerized Imaging Reference Systems, Norfolk, VA). Details are shown in the following.…”

Section: A General Scheme Of the Mm-fd Techniquementioning

confidence: 99%

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Dosimetric verification of lung cancer treatment using the CBCTs estimated from limited‐angle on‐board projections

2015

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Purpose: Lung cancer treatment is susceptible to treatment errors caused by interfractional anatomical and respirational variations of the patient. On-board treatment dose verification is especially critical for the lung stereotactic body radiation therapy due to its high fractional dose. This study investigates the feasibility of using cone-beam (CB)CT images estimated by a motion modeling and free-form deformation (MM-FD) technique for on-board dose verification. Methods: Both digital and physical phantom studies were performed. Various interfractional variations featuring patient motion pattern change, tumor size change, and tumor average position change were simulated from planning CT to on-board images. The doses calculated on the planning CT (planned doses), the on-board CBCT estimated by MM-FD (MM-FD doses), and the on-board CBCT reconstructed by the conventional Feldkamp-Davis-Kress (FDK) algorithm (FDK doses) were compared to the on-board dose calculated on the "gold-standard" on-board images (gold-standard doses). The absolute deviations of minimum dose (∆D min ), maximum dose (∆D max ), and mean dose (∆D mean ), and the absolute deviations of prescription dose coverage (∆V 100% ) were evaluated for the planning target volume (PTV). In addition, 4D on-board treatment dose accumulations were performed using 4D-CBCT images estimated by MM-FD in the physical phantom study. The accumulated doses were compared to those measured using optically stimulated luminescence (OSL) detectors and radiochromic films. Results: Compared with the planned doses and the FDK doses, the MM-FD doses matched much better with the gold-standard doses. For the digital phantom study, the average (± standard deviation) ∆D min , ∆D max , ∆D mean , and ∆V 100% (values normalized by the prescription dose or the total PTV) between the planned and the gold-standard PTV doses were 32.9% (±28.6%), 3.0% (±2.9%), 3.8% (±4.0%), and 15.4% (±12.4%), respectively. The corresponding values of FDK PTV doses were 1.6% (±1.9%), 1.2% (±0.6%), 2.2% (±0.8%), and 17.4% (±15.3%), respectively. In contrast, the corresponding values of MM-FD PTV doses were 0.3% (±0.2%), 0.9% (±0.6%), 0.6% (±0.4%), and 1.0% (±0.8%), respectively. Similarly, for the physical phantom study, the average ∆D min , ∆D max , ∆D mean , and ∆V 100% of planned PTV doses were 38.1% (±30.8%), 3.5% (±5.1%), 3.0% (±2.6%), and 8.8% (±8.0%), respectively. The corresponding values of FDK PTV doses were 5.8% (±4.5%), 1.6% (±1.6%), 2.0% (±0.9%), and 9.3% (±10.5%), respectively. In contrast, the corresponding values of MM-FD PTV doses were 0.4% (±0.8%), 0.8% (±1.0%), 0.5% (±0.4%), and 0.8% (±0.8%), respectively. For the 4D dose accumulation study, the average (± standard deviation) absolute dose deviation (normalized by local doses) between the accumulated doses and the OSL measured doses was 3.3% (±2.7%). The average gamma index (3%/3 mm) between the accumulated doses and the radiochromic film measured doses was 94.5% (±2.5%). Conclusions: MM-FD estimated 4D-CBCT enables accurate on-board do...

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Estimating 4D‐CBCT from prior information and extremely limited angle projections using structural PCA and weighted free‐form deformation for lung radiotherapy

et al. 2017

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Purpose To investigate the feasibility of using structural-based principal component analysis (PCA) motion-modeling and weighted free-form deformation to estimate on-board 4D-CBCT using prior information and extremely 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 the previous method, each phase of the 4D-CBCT was generated by deforming a prior CT volume. The DFM was solved by a motion-model extracted by global PCA and free-form deformation (GMM-FD) technique, using a data fidelity constraint and deformation energy minimization. In this study, a new structural-PCA method was developed to build a structural motion-model (SMM) by accounting for potential relative motion pattern changes between different anatomical structures from simulation to treatment. The motion model extracted from planning 4DCT was divided into two structures: tumor and body excluding tumor, and the parameters of both structures were optimized together. Weighted free-form deformation (WFD) was employed afterwards to introduce flexibility in adjusting the weightings of different structures in the data fidelity constraint based on clinical interests. XCAT (computerized patient model) simulation with a 30 mm diameter lesion was simulated with various anatomical and respirational changes from planning 4D-CT to onboard volume to evaluate the method. The estimation 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. Different onboard projection acquisition scenarios and projection noise levels were simulated to investigate their effects on the estimation accuracy. The method was also evaluated against 3 lung patients. Results The SMM-WFD method achieved substantially better accuracy than the GMM-FD method for CBCT estimation using extremely small scan angles or projections. Using orthogonal 15° scanning angles, the VPD/COMS were 3.47±2.94% and 0.23±0.22mm for SMM-WFD and 25.23±19.01% and 2.58±2.54mm for GMM-FD among all 8 XCAT scenarios. Compared to GMM-FD, SMM-WFD was more robust against reduction of the scanning angles down to orthogonal 10° with VPD/COMS of 6.21±5.61% and 0.39±0.49mm, and more robust against reduction of projection numbers down to only 8 projections in total for both orthogonal-view 30° and orthogonal-view 15° scan angles. SMM-WFD method was also more robust than the GMM-FD method against increasing levels of noise in the projection images. Additionally, the SMM-WFD technique provided better tumor estimation for all three lung patients compared to the GMM-FD technique. Conclusion Compared to the GMM-FD technique, the SMM-WFD technique can substantially improve the 4D-CBCT estimation accuracy using extremely small scan angles and low number of projections to provide fast low dose 4D target verification.

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

Abstract: 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.

Cited by 83 publications

References 53 publications

3D delivered dose assessment using a 4DCT-based motion model

3D delivered dose assessment using a 4DCT-based motion model

Dosimetric verification of lung cancer treatment using the CBCTs estimated from limited‐angle on‐board projections

Estimating 4D‐CBCT from prior information and extremely limited angle projections using structural PCA and weighted free‐form deformation for lung radiotherapy

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