A comprehensive evaluation of the accuracy of CBCT and deformable registration based dose calculation in lung proton therapy

The uncertainties in water equivalent thickness (WET) and accuracy of dose estimation using a virtual CT (vCT), generated from deforming the planning CT (pCT) onto the daily cone-beam CT (CBCT), were comprehensively evaluated in the context of lung malignancies and passive scattering proton therapy. The validation methodology utilized multiple CBCT datasets to generate the vCTs of twenty lung cancer patients. A correction step was applied to the vCTs to account for anatomical modifications that could not be modeled by deformation alone. The CBCT datasets included a regular CBCT (rCBCT) and synthetic CBCTs created from the rCBCT and rescan CT (rCT), which minimized the variation in setup between the vCT and the gold-standard image (i.e., rCT). The uncertainty in WET was defined as the voxelwise difference in WET between vCT and rCT, and calculated in 3D (planning target volume, PTV) and 2D (distal and proximal surfaces). The uncertainty in WET based dose warping was defined as the difference between the warped dose and a forward dose recalculation on the rCT. The overall root mean square (RMS) uncertainty in WET was 3.6 ± 1.8, 2.2 ± 1.4 and 3.3 ± 1.8 mm for the distal surface, proximal surface and PTV, respectively. For the warped dose, the RMS uncertainty of the voxelwise dose difference was 6% ± 2% of the maximum dose (%mD), using a 20% cut-off. The rCBCT resulted in higher uncertainties due to setup variability with the rCT; the uncertainties reported with the two synthetic CBCTs were similar. The vCT followed by a correction step was found to be an accurate alternative to rCT

Modeling of Wake-Vortex Detection by a Ground-based Fiber LIDAR System

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The Reconstruction Toolkit (RTK), an open-source cone-beam CT reconstruction toolkit based on the Insight Toolkit (ITK)

International audiencePurpose: To develop an open-source toolkit for fast cone-beam CT reconstruction based on the Insight Toolkit. Methods: We have started the Reconstruction Toolkit (RTK, http://www.openrtk.org), an open-source toolkit for cone-beam CT reconstruction, based on the Insight Toolkit (ITK, http://www.itk.org/) and using GPU code extracted from Plastimatch (http://www.plastimatch.org/). RTK is developed by an open consortium (see affiliations) under the non- contaminating Apache 2.0 license. The quality of the platform is daily checked with regression tests in partnership with Kitware which already supports ITK. Results: Several features are already available: Elekta, Varian and IBA inputs, multi-threaded Feldkamp-David-Kress reconstruction on CPU and GPU, Parker short scan weighting, multi-threaded CPU and GPU forward projectors, etc. Each feature is either accessible through command line tools or C++ classes that can be included in independent software. A MIDAS community (http://midas3.kitware.com) has been opened to provide CatPhan datasets of several vendors (Elekta, Varian and IBA). RTK will be used in the upcoming cone-beam CT scanner developed by IBA for proton therapy rooms. Many features are under development: new input format support, iterative reconstruction, hybrid Monte Carlo / deterministic CBCT simulation, etc. Conclusions: RTK has been built to freely share tomographic reconstruction development between researchers and is open for new contributions

Simulation of x-ray images from the planning CT for online correction of scatter in cone-beam CT

International audiencePurpose/Objective: To correct for scatter in cone-beam CT images and to calibrate the image intensities in Hounsfield units (HU) using fast and accurate simulation of x-ray images of the planning CT

Design of cone-beam CT for proton therapy gantry

International audiencePurpose/Objective: Cone-beam CT is widely used in radiation therapy proving tremendous interest for patient positioning and daily monitoring of anatomical modifications. Moreover, the use of volumetric imaging can contribute to a more accurate location of the target volume which is important in proton therapy (PT) where sharp dose gradients are used. Despite this potential advantage, integrating a CBCT on a PT gantry has not already been done and poses additional challenges such as potentially larger geometrical deformations compared to a LINAC (Table 1). In this paper, we describe how the first CBCT has been implemented in a PT gantry.The general design, choice of hardware, and software implementation are outlined and results on a phantom demonstrate the possibilities of the system

Design of cone-beam CT for proton therapy gantry

International audiencePurpose/Objective: Cone-beam CT is widely used in radiation therapy proving tremendous interest for patient positioning and daily monitoring of anatomical modifications. Moreover, the use of volumetric imaging can contribute to a more accurate location of the target volume which is important in proton therapy (PT) where sharp dose gradients are used. Despite this potential advantage, integrating a CBCT on a PT gantry has not already been done and poses additional challenges such as potentially larger geometrical deformations compared to a LINAC (Table 1). In this paper, we describe how the first CBCT has been implemented in a PT gantry.The general design, choice of hardware, and software implementation are outlined and results on a phantom demonstrate the possibilities of the system

The Reconstruction Toolkit (RTK) : an open-source cone-beam CT reconstruction toolkit based on the Insight Toolkit (ITK)

We propose the Reconstruction Toolkit (RTK, http://www.openrtk.org), an open-source toolkit for fast cone-beam CT reconstruction, based on the Insight Toolkit (ITK) and using GPU code extracted from Plastimatch. RTK is developed by an open consortium (see affiliations) under the non-contaminating Apache 2.0 license. The quality of the platform is daily checked with regression tests in partnership with Kitware, the company supporting ITK. Several features are already available: Elekta, Varian and IBA inputs, multi-threaded Feldkamp-David-Kress reconstruction on CPU and GPU, Parker short scan weighting, multi-threaded CPU and GPU forward projectors, etc. Each feature is either accessible through command line tools or C++ classes that can be included in independent software. A MIDAS community has been opened to share CatPhan datasets of several vendors (Elekta, Varian and IBA). RTK will be used in the upcoming cone-beam CT scanner developed by IBA for proton therapy rooms. Many features are under development: new input format support, iterative reconstruction, hybrid Monte Carlo / deterministic CBCT simulation, etc. RTK has been built to freely share tomographic reconstruction developments between researchers and is open for new contributions

Anthropomorphic lung phantom based validation of in-room proton therapy 4D-CBCT image correction for dose calculation.

PURPOSE: Ventilation-induced tumour motion remains a challenge for the accuracy of proton therapy treatments in lung patients. We investigated the feasibility of using a 4D virtual CT (4D-vCT) approach based on deformable image registration (DIR) and motion-aware 4D CBCT reconstruction (MA-ROOSTER) to enable accurate daily proton dose calculation using a gantry-mounted CBCT scanner tailored to proton therapy. METHODS: Ventilation correlated data of 10 breathing phases were acquired from a porcine ex-vivo functional lung phantom using CT and CBCT. 4D-vCTs were generated by (1) DIR of the mid-position 4D-CT to the mid-position 4D-CBCT (reconstructed with the MA-ROOSTER) using a diffeomorphic Morphons algorithm and (2) subsequent propagation of the obtained mid-position vCT to the individual 4D-CBCT phases. Proton therapy treatment planning was performed to evaluate dose calculation accuracy of the 4D-vCTs. A robust treatment plan delivering a nominal dose of 60Gy was generated on the average intensity image of the 4D-CT for an approximated internal target volume (ITV). Dose distributions were then recalculated on individual phases of the 4D-CT and the 4D-vCT based on the optimized plan. Dose accumulation was performed for 4D-vCT and 4D-CT using DIR of each phase to the mid position, which was chosen as reference. Dose based on the 4D-vCT was then evaluated against the dose calculated on 4D-CT both, phase-by-phase as well as accumulated, by comparing dose volume histogram (DVH) values (Dmean, D2%, D98%, D95%) for the ITV, and by a 3D-gamma index analysis (global, 3%/3mm, 5Gy, 20Gy and 30Gy dose thresholds). RESULTS: Good agreement was found between the 4D-CT and 4D-vCT-based ITV-DVH curves. The relative differences ((CT-vCT)/CT) between accumulated values of ITV Dmean, D2%, D95% and D98% for the 4D-CT and 4D-vCT-based dose distributions were -0.2%, 0.0%, -0.1% and -0.1%, respectively. Phase specific values varied between -0.5% and 0.2%, -0.2% and 0.5%, -3.5% and 1.5%, and -5.7% and 2.3%. The relative difference of accumulated Dmean over the lungs was 2.3% and Dmean for the phases varied between -5.4% and 5.8%. The gamma pass-rates with 5Gy, 20Gy and 30Gy thresholds for the accumulated doses were 96.7%, 99.6% and 99.9%, respectively. Phase-by-phase comparison yielded pass-rates between 86% and 97%, 88% and 98%, and 94% and 100%. CONCLUSIONS: Feasibility of the suggested 4D-vCT workflow using proton therapy specific imaging equipment was shown. Results indicate the potential of the method to be applied for daily 4D proton dose estimation