Evaluation Of Geometric Accuracy Research Articles

The Process of Digital Data Flow in RE/CAD/RP/CAI Systems Concerning Planning Surgical Procedures in the Craniofacial Area

This paper presents the process of digital data flow in RE/CAD/RP/CAI systems to develop models for planning surgical procedures in the craniofacial area. At the first RE modeling stage, digital data processing, segmentation, and the reconstruction of the geometry of the anatomical structures were performed. During the CAD modeling stage, three different concepts were utilized. The first concept was used to create a tool that could mold the geometry of the cranial vault. The second concept was created to prepare a prototype implant that would complement the anterior part of the mandibular geometry. And finally, the third concept was used to design a customized prototype surgical plate that would match the mandibular geometry accurately. Physical models were made using a rapid prototyping technique. A Bambu Lab X1 3D printer was used for this purpose. The process of geometric accuracy evaluation was carried out on manufactured prototypes of surgical plates made of ABS+, CPE, PLA+, and PETG material. In the geometric accuracy evaluation process, the smallest deviation values were obtained for the ABS plus material, within a tolerance of ±0.1 mm, and the largest were obtained for CPE (±0.2 mm) and PLA plus (±0.18 mm). In terms of the surface roughness evaluation, the highest value of the Sa parameter was obtained for the PLA plus material, which was 4.15 µm, and the lowest was obtained for the CPE material, equal to 3.62 µm. The knowledge of the flow of digital data and the identification of factors determining the accuracy of mapping the geometry of anatomical structures allowed for the development of a procedure that improves the modeling and manufacturing of anatomical structures within the craniofacial region.

Geometric accuracy evaluation and analysis of ZY-1 02E IRS thermal infrared image data using GCP extraction based on phase correlation matching method

Abstract. The Ziyuan-1 (ZY-1) 02E launched on December 26, 2021 is equipped with a thermal infrared sensor (IRS), which has a ground resolution of better than 16m and a width priority of 115km, balancing the advantages of high resolution and large wide observation. The geometric performance of image data is the premise of remote sensing application, and the difficulty in evaluating the geometric performance of thermal infrared image data lies in the extraction of well-distributed, reliable and accurate GCPs. To extract GCP from high-precision reference images, it is necessary to overcome the feature differences between images caused by different spectral responses. This paper adopts a phase correlation matching method based on frequency domain to realize the fine registration of the data obtained by the emission thermal spectral band with the data from the reflectance spectral band, which can not only solve the GCP extraction of conventional thermal infrared images collected during the day, but also obtain satisfactory GCP data from thermal infrared data acquired at night. In order to test the GCP method proposed in this paper, three typical areas are selected as the experimental areas, including Yiyang City in Hunan, Nagqu City in Xizang and Hami City in Xinjiang, and the internal geometric accuracy and absolute geolocation accuracy of the thermal infrared data spanning one year are evaluated and analyzed by using the reference data composed of the DOM with an accuracy of 2m and the DEM with an accuracy of 10m. The research results indicate that the internal geometric accuracy of ZY-1 02E IRS satellite image data is better than 1.0 pixels, and the performance is satisfactory. However, its absolute geolocation accuracy needs to be continuously improved, especially there are systematic errors in the ascending data at night that require further research. Overall, it meets the design accuracy indicators of satellites and can meet the application requirements of thermal infrared remote sensing.

Respiratory motion modelling for MR-guided lung cancer radiotherapy: model development and geometric accuracy evaluation.

Objective.Respiratory motion of lung tumours and adjacent structures is challenging for radiotherapy. Online MR-imaging cannot currently provide real-time volumetric information of the moving patient anatomy, therefore limiting precise dose delivery, delivered dose reconstruction, and downstream adaptation methods.Approach.We tailor a respiratory motion modelling framework towards an MR-Linac workflow to estimate the time-resolved 4D motion from real-time data. We develop a multi-slice acquisition scheme which acquires thick, overlapping 2D motion-slices in different locations and orientations, interleaved with 2D surrogate-slices from a fixed location. The framework fits a motion model directly to the input data without the need for sorting or binning to account for inter- and intra-cycle variation of the breathing motion. The framework alternates between model fitting and motion-compensated super-resolution image reconstruction to recover a high-quality motion-free image and a motion model. The fitted model can then estimate the 4D motion from 2D surrogate-slices. The framework is applied to four simulated anthropomorphic datasets and evaluated against known ground truth anatomy and motion. Clinical applicability is demonstrated by applying our framework to eight datasets acquired on an MR-Linac from four lung cancer patients.Main results.The framework accurately reconstructs high-quality motion-compensated 3D images with 2 mm3isotropic voxels. For the simulated case with the largest target motion, the motion model achieved a mean deformation field error of 1.13 mm. For the patient cases residual error registrations estimate the model error to be 1.07 mm (1.64 mm), 0.91 mm (1.32 mm), and 0.88 mm (1.33 mm) in superior-inferior, anterior-posterior, and left-right directions respectively for the building (application) data.Significance.The motion modelling framework estimates the patient motion with high accuracy and accurately reconstructs the anatomy. The image acquisition scheme can be flexibly integrated into an MR-Linac workflow whilst maintaining the capability of online motion-management strategies based on cine imaging such as target tracking and/or gating.

Geometric Accuracy Evaluation Method for Subway Stations Based on 3D Laser Scanning

The rapid development of three-dimensional (3D) laser scanning technology has provided a new technical means for the geometric accuracy evaluation of subway stations. With high precision and high efficiency, laser scanning technology can present the construction site condition in a panoramic way, which is essential for achieving high precision and all-round geometric accuracy evaluation. However, when the survey coordinate system of the design building information modeling (BIM) predefined in the design stage is not applied during the laser scanning data acquisition or the BIM loses the survey coordinate system during the interaction, the objects will have different coordinate positions in the point cloud and BIM, which will limit the accuracy comparison between the two data sources. Meanwhile, the existing methods mainly focus on the above overground buildings, and the accuracy evaluation of underground structures mainly focuses on the overall deformation monitoring. So far, the existing methods do not constitute a hierarchical index system to assess the geometric accuracy of various objects in the subway station. This study proposes a method to evaluate the geometric accuracy of subway stations based on laser scanning technology. A coarse-to-fine coordinate registration from point cloud to the design BIM is used to unify coordinates in different reference systems; and geometric accuracy evaluation of different structures in subway stations is achieved by developing geometric accuracy evaluation indexes and technical systems. The method is applied to the geometric accuracy monitoring of the Hongqi Road subway station, and the experimental results verify the reliability of the method.

Deep learning model for automatic contouring of cardiovascular substructures on radiotherapy planning CT images: Dosimetric validation and reader study based clinical acceptability testing

Background and purposeLarge radiotherapy (RT) planning imaging datasets with consistently contoured cardiovascular structures are essential for robust cardiac radiotoxicity research in thoracic cancers. This study aims to develop and validate a highly accurate automatic contouring model for the heart, cardiac chambers, and great vessels for RT planning computed tomography (CT) images that can be used for dose–volume parameter estimation. Materials and methodsA neural network model was trained using a dataset of 127 expertly contoured planning CT images from RT treatment of locally advanced non-small-cell lung cancer (NSCLC) patients. Evaluation of geometric accuracy and quality of dosimetric parameter estimation was performed on 50 independent scans with contrast and without contrast enhancement. The model was further evaluated regarding the clinical acceptability of the contours in 99 scans randomly sampled from the RTOG-0617 dataset by three experienced radiation oncologists. ResultsMedian surface dice at 3 mm tolerance for all dedicated thoracic structures was 90% in the test set. Median absolute difference between mean dose computed with model contours and expert contours was 0.45 Gy averaged over all structures. The mean clinical acceptability rate by majority vote in the RTOG-0617 scans was 91%. ConclusionThis model can be used to contour the heart, cardiac chambers, and great vessels in large datasets of RT planning thoracic CT images accurately, quickly, and consistently. Additionally, the model can be used as a time-saving tool for contouring in clinic practice.

Fluoroscopic Guidance of a Surgical Robot: Pre-clinical Evaluation in Pelvic Guidewire Placement.

A method and prototype for a fluoroscopically-guided surgical robot is reported for assisting pelvic fracture fixation. The approach extends the compatibility of existing guidance methods with C-arms that are in mainstream use (without prior geometric calibration) using an online calibration of the C-arm geometry automated via registration to patient anatomy. We report the first preclinical studies of this method in cadaver for evaluation of geometric accuracy. The robot is placed over the patient within the imaging field-of-view and radiographs are acquired as the robot rotates an attached instrument. The radiographs are then used to perform an online geometric calibration via 3D-2D image registration, which solves for the intrinsic and extrinsic parameters of the C-arm imaging system with respect to the patient. The solved projective geometry is then be used to register the robot to the patient and drive the robot to planned trajectories. This method is applied to a robotic system consisting of a drill guide instrument for guidewire placement and evaluated in experiments using a cadaver specimen. Robotic drill guide alignment to trajectories defined in the cadaver pelvis were accurate within 2 mm and 1° (on average) using the calibration-free approach. Conformance of trajectories within bone corridors was confirmed in cadaver by extrapolating the aligned drill guide trajectory into the cadaver pelvis. This study demonstrates the accuracy of image-guided robotic positioning without prior calibration of the C-arm gantry, facilitating the use of surgical robots with simpler imaging devices that cannot establish or maintain an offline calibration. Future work includes testing of the system in a clinical setting with trained orthopaedic surgeons and residents.

Geometric accuracy evaluation of a six-degree-of-freedom (6-DoF) couch with cone beam computed tomography (CBCT) using a phantom and correlation study of the position errors in pelvic tumor radiotherapy.

BackgroundTo assess the position accuracy of the six-degree-of-freedom (6-DoF) couch based on cone beam computed tomography (CBCT) and exploit the correlation of the six degrees errors.MethodsCT scans of an anthropomorphic phantom and patients were obtained at 3 mm slice thicknesses using a Philips scanner at the head, first supine and prostrate positions. An Eclipse Treatment Planning System was used to create a treatment plan. Different levels of known position errors were introduced to simulate patient position status for the anthropomorphic phantom. CBCT datasets for each position were acquired and registered to original CT datasets to evaluate the accuracy of the 6-DoF couch and determine the setup errors of patients. The setup errors of 200 CBCT datasets from 14 patients with pelvic tumors were analyzed. The correlations between six degrees position errors were finally extracted.ResultsFor the phantom study, the difference between known introduced errors and the setup errors were almost negligible. The deviation (mean ± one standard deviation) in registration methods were (0.01±0.02) cm, (0.04±0.075) cm, (0.02±0.004) cm, (0.01±0.04)°, (0.1±0.08)°, (0.03±0.05)° and (0.01±0.01) cm, (0.03±0.007) cm, (0.01±0.01) cm, (0.05±0.06)°, (0.08±0.08)°, (0.04±0.05)° for supine and prone position, respectively. The deviation in positions were (0.07±0.10) cm, (0.16±0.02) cm, (0.08±0.06) cm, (0.54±0.46)°, (0.24±0.16)°, (0.09±0.09)° and (0.06±0.09) cm, (0.19±0.09) cm, (0.09±0.07) cm, (0.49±0.49)°, (0.16±0.08)°, (0.1±0.13)° for bone and soft tissue registration methods, respectively. For patient data, the setup errors were (−0.07±0.22) cm, (0.14±0.35) cm, (−0.12±0.4) cm, (0.79±1.6)°, (0.41±0.71)°, (−0.03±0.8)° for supine position and (0.16±0.27) cm, (0.19±0.48) cm, (−0.05±0.34) cm, (1.1±1.49)°, (0.65±1.00)°, (−0.23±0.75)° for prone position, respectively. There is a significant moderate correlation between the longitudinal and pitch directions and between the vertical and pitch directions when the patient is in the supine position.ConclusionsThe six-dimensional couch positioning verification system based on CBCT has high accuracy and can meet the requirements of precise radiotherapy for pelvic tumors. There is a certain correlation between translation direction and rotation direction.

THE OVERSEAS GEOMETRIC ACCURACY VALIDATION OF ZY-3 SATELLITES IMAGES

Abstract. With China’s first stereo imaging satellite ZY-3’s successful launch and two satellites networking operation, space remote sensing becomes an important means of data acquisition for survey and mapping, and geographic information updating in China.The updating period of 4D products in China is shortened by one third, the geographic information updating capability was improved more than 2 times.After more than eight years of stable and continued earth observation, ZY-3 statellites data coverage has gradually achieved more than half of the earth land which enables the overseas service for global geospatial application. Focusing on the Chinese domestic mapping applications and services, the data of ZY-3 and other domestic land observation satellites can be real-time pushed and distributed across China through the satellite cloud service platform, and worldwide for facilitating the "Belt and Road" initiative, which is promoted through the GEOSS as well for global application.This paper presents the overseas geometric accuracy evaluation and validation of ZY-3 satellites images, which was carried out systematically for the first time abroad and complements with China’s mapping evaluation practices to provide a comprehensive technical guidelines for global mapping application. The direct location accuracy of ZY-3 satellites sensor corrected image products were further evaluated and verified cooperating with the University of Vienna, Austria. The location deviations in mountain area and in flat area were analyzed and compared to check the deviation pattern and validate their consistency with the results in China.Utilizing China’s ZY-3 satellites images ranging from 2012–2018, the DSM was generated automatically based on a semiglobal optimization method (Yue et al. 2016) using self-developed software SDP without ground control points but using SRTM data as elevation reference to improve the geometric accuracy. The result shows the elevation accuracy of DSM is 3.19 m (RMSE), satisfying the local requirement for 10m interval contour mapping.The planar accuracy of DOM generated without ground control points utilizing ZY-3 satellites images within 2012–2015 is 2.46 m (RMSE). With 128 orthorectified aerial photo slots provided by NGD of Laos as reference, the planar accuracy of the DOM generated utilizing ZY-3 satellites images from 2016–2018 is 1.65 m (RMSE), which can satisfy the local 1:25000 planar accuracy requirement and overlay with the local 1:2000 transportation data exactly. The overseas geometric accuracy evaluation and validation of ZY-3 satellites images provides a systematic and practical guidance for future global applications by complementing with china’s experience, which would be beneficial to overseas users in acknowledging the usage of ZY-3 satellites data and help to promote it’s global applications.

Geometric accuracy evaluation during coordinated motion of rotary axes of a five-axis machine tool

This paper presents a novel method to identify Position Independent Geometric Errors (PIGEs) of a five-axis machine tool with a tilting head and a rotary table using a Double Ballbar (DBB). A newly defined measuring trajectory only involving both rotary axes coordinated motion is proposed. The DBB is used to capture conic deviations that are used to generate error trace patterns. The asynchronisation between the resultant speed of the spindle tool cup during the B- and C-axes coordinated motion and the DBB capture speed has been resolved, enabling the true reflection of machine tool error conditions. The testing results are compared with simulation results established using the Homogeneous Transformation Matrices (HTMs) in conjunction with the rigid body kinematics. Different PIGEs were both estimated and measured using the simulation model and the proposed testing method respectively. Disagreements in the simulation and experimental results are analysed. The residual error after compensation of the PIGEs accounts for 8.76% of the total error budget, which might be due to thermal errors and kinematic errors. Experimental results show that the compensation of the PIGEs diagnosed in this paper will significantly enhance the coordinated motion of the B- and C-axes. Since the measurement involves both axes moving simultaneously, it can not only reflect the PIGEs of each rotary axes, but also assesses the geometric and kinematic coordination between the two rotary axes, which could comprehensively reflect the geometric accuracy of the five-axis machine tool.

Using a 3D Printed Model as a Preoperative Tool for Pelvic Triple Osteotomy in Children: Proof of Concept and Evaluation of Geometric Accuracy.

The feasibility of 3D printing in clinical practice depends not only on the usability but also on the reliability of the method. The aims of this study were to demonstrate the feasibility of a 3D printing method for pediatric patients planned for pelvic triple osteotomy and to present a reliable quality assessment strategy for these printed models. A 10-year-old boy with Legg-Calvé-Perthes disease underwent a triple pelvic osteotomy. Preoperative and postoperative CT scans were printed as 3D models. An image-based quality assessment strategy was proposed: The printed 3D models were imaged with CT. The model images were systematically compared with the corresponding ground truth images, ie, patient images, to determine the reliability using distance measurements in the model and ground truth images. The 3D printed models were found useful in both the preoperative and postoperative stages. The models were found reliable: Strong linear correlation between the model and ground truth images both preoperatively (R = 0.99; P < 0.001) and postoperatively (R = 1.00; P < 0.001) was found. The study demonstrates the usefulness of 3D printed models in clinical practice. We also present a robust and simple strategy, using common clinical tools, to assess the reliability of 3D printed models.

AN AUTOMATED SOFTWARE FRAMEWORK FOR EVALUATION AND IMPROVEMENT OF ABSOLUTE GEOMETRIC LOCATION ACCURACY OF MULTISPECTRAL REMOTE SENSING SATELLITE IMAGERY

Abstract. Geometric accuracy is an important parameter for quality assessment of a data product and is vital for certain applications aiming on improving and bringing precision in data products. Automatic geometric accuracy evaluation of the satellite image is attempted by matching a known, surveyed location typically a ground control point (GCP) calibrated using a differential global positioning system (DGPS), verified using Google Maps, to the corresponding identifiable feature in an image product. The requirement for this development is to address the non-uniformity in the available data products in terms of coordinates reference system, resolution and available bands, which the software overcomes successfully by benefiting from the classes and functions available in openly available GIS libraries. RMSE of 0.8 pixels is found in analysis for the chosen data. Further, an algorithm is worked up to rectify the image for this geometric shift.

"Patient-specific validation of deformable image registration in radiation therapy: Overview and caveats".

Over the last few decades, deformable image registration (DIR) has gained popularity in image-guided radiation therapy for a number of applications, such as contour propagation, dose warping, and accumulation. Although this raises promising perspectives for the improvement of treatment outcomes and quality of radiotherapy clinical practice, the variety of proposed DIR algorithms, combined with the lack of an effective quantitative quality control metric of the registration, is slowing the transfer of DIR into the clinical routine. Recently, a task group (AAPM TG132) report was published outlining the essential aspects of DIR for image guidance in radiotherapy. However, an accurate and efficient patient-specific validation is not yet defined, and appropriate metrics should be identified to achieve the definition of both geometric and dosimetric accuracy. In this respect, the use of a dense set of anatomical landmarks, along with additional evaluations on contours or deformation field analysis, are likely to drive patient-specific DIR validation in clinical image-guided radiotherapy applications to account for geometric inaccuracies. Automatic and efficient strategies able to provide spatial information of DIR uncertainties and to evaluate monomodal and multimodal image registration, as well as to describe homogenous and un-contrasted regions are believed to represent the future direction in DIR validation. But especially in the case of DIR applications for dose mapping and accumulation, the need of accurate patient-specific validation is not only limited to the evaluation of geometric accuracy. In fact, the need to account for dosimetric inaccuracies due to DIR represents another important area in the field of adaptive treatments. Different approaches are currently being investigated to quantify the effect of DIR error on dose analysis, mainly relying on clinically relevant dose metrics, or on the study of deformation field properties for a voxel-by-voxel evaluation. However, novel research is required for the definition of dedicated and personalized measures capable to relate the geometric and dosimetric inaccuracies, thus bearing useful information for a safe use of DIR by clinical end users. In this paper we provide insights on DIR results evaluation on a patient-specific basis, facing the issues of both geometric and dosimetric paradigms. Challenges on DIR validation are overviewed and discussed, in order to push preliminary clinical guidelines forward on this fundamental topic and boost the implementation of more robust and reliable patient-specific evaluation metrics.

Geometric Accuracy Evaluation of High-Resolution Satellite Images Based on Xianning Test Field.

The evaluation of geometric accuracy of high-resolution satellite images (HRSIs) has been increasingly recognized in recent years. The traditional approach is to verify each satellite individually. It is difficult to directly compare the difference in their accuracy. In order to evaluate geometric accuracy for multiple satellite images based on the same ground control benchmark, a reliable test field in Xianning (China) was utilized for geometric accuracy validation of HRSIs. Our research team has obtained multiple HRSIs in the Xianning test field, such as SPOT-6, Pleaides, ALOS, ZY-3 and TH-1. In addition, ground control points (GCPs) were acquired with GPS by field surveying, which were used to select the significant feature area on the images. We assess the orientation accuracy of the HRSIs with the single image and stereo models. Within this study, the geometrical performance of multiple HRSIs was analyzed in detail, and the results of orientation are shown and discussed. As a result, it is feasible and necessary to establish such a geometric verification field to evaluate the geometric quality of multiple HRSIs.

Large-scale subject-specific cerebral arterial tree modeling using automated parametric mesh generation for blood flow simulation

In this paper, we present a novel technique for automatic parametric mesh generation of subject-specific cerebral arterial trees. This technique generates high-quality and anatomically accurate computational meshes for fast blood flow simulations extending the scope of 3D vascular modeling to a large portion of cerebral arterial trees. For this purpose, a parametric meshing procedure was developed to automatically decompose the vascular skeleton, extract geometric features and generate hexahedral meshes using a body-fitted coordinate system that optimally follows the vascular network topology. To validate the anatomical accuracy of the reconstructed vasculature, we performed statistical analysis to quantify the alignment between parametric meshes and raw vascular images using receiver operating characteristic curve. Geometric accuracy evaluation showed an agreement with area under the curves value of 0.87 between the constructed mesh and raw MRA data sets. Parametric meshing yielded on-average, 36.6% and 21.7% orthogonal and equiangular skew quality improvement over the unstructured tetrahedral meshes. The parametric meshing and processing pipeline constitutes an automated technique to reconstruct and simulate blood flow throughout a large portion of the cerebral arterial tree down to the level of pial vessels. This study is the first step towards fast large-scale subject-specific hemodynamic analysis for clinical applications.

Geometric Accuracy Evaluation of YG‐18 Satellite Imagery Based on RFM

AbstractYaoGan‐18 (YG‐18) is a Chinese high‐resolution synthetic aperture radar (SAR) satellite, which was launched on 29th October 2013. So far, however, there have been no published reports evaluating the geometric accuracy of its imagery; this is rectified in this paper. A refined rational function model (RFM) with an affine transformation is utilised for the spaceborne SAR processing. By setting corner reflectors as ground control points (GCPs) and independent check points, the orthorectification accuracy of YG‐18 satellite images was better than 2·5 m. Its stereo‐SAR measurement accuracy was subsequently evaluated using a high‐precision digital surface model (DSM), achieving an elevation accuracy of 11·36 m. The feasibility of the orthorectification method based on GCPs selected from corresponding image points of YG‐18 SAR images and ZiYuan‐3 (ZY‐3) optical images was also verified, offering single‐image accuracy better than 4·5 m.

Multicenter Evaluation of Geometric Accuracy of MRI Protocols Used in Experimental Stroke.

It has recently been suggested that multicenter preclinical stroke studies should be carried out to improve translation from bench to bedside, but the accuracy of magnetic resonance imaging (MRI) scanners routinely used in experimental stroke has not yet been evaluated. We aimed to assess and compare geometric accuracy of preclinical scanners and examine the longitudinal stability of one scanner using a simple quality assurance (QA) protocol. Six 7 Tesla animal scanners across six different preclinical imaging centers throughout Europe were used to scan a small structural phantom and estimate linear scaling errors in all orthogonal directions and volumetric errors. Between-scanner imaging consisted of a standard sequence and each center’s preferred sequence for the assessment of infarct size in rat models of stroke. The standard sequence was also used to evaluate the drift in accuracy of the worst performing scanner over a period of six months following basic gradient calibration. Scaling and volumetric errors using the standard sequence were less variable than corresponding errors using different stroke sequences. The errors for one scanner, estimated using the standard sequence, were very high (above 4% scaling errors for each orthogonal direction, 18.73% volumetric error). Calibration of the gradient coils in this system reduced scaling errors to within ±1.0%; these remained stable during the subsequent 6-month assessment. In conclusion, despite decades of use in experimental studies, preclinical MRI still suffers from poor and variable geometric accuracy, influenced by the use of miscalibrated systems and various types of sequences for the same purpose. For effective pooling of data in multicenter studies, centers should adopt standardized procedures for system QA and in vivo imaging.

Evaluation of the performance of KOMPSAT-3 stereo images in terms of positioning and the generation of digital surface models

ABSTRACTKOMPSAT-3 is an optical high-resolution earth observation satellite launched on 19 May 2012. It provides panchromatic optical images at a nominal ground sampling distance (GSD) of 70 cm. This letter provides geometric accuracy evaluation of KOMPSAT-3 stereo images, including position determination and automated digital surface model (DSM) generation. Bias-compensated KOMPSAT-3 stereo achieved positioning accuracy of 0.65 m and 0.70 m in horizontal and vertical directions, respectively. Bias-compensated KOMPSAT-3 images were utilized for automated DSM generation. A DSM showed height errors of about 3.8 m (RMS) when all grids were compared with reference LIDAR data. Geometric performance of KOMPSAT-3 images was also compared with that of WorldView-1 images whose nominal GSD is 46 cm, over the same test area. The positioning accuracy and the accuracy of DSM generation from KOMPSAT-3 were slightly inferior to those of WorldView-1. However, overall performance of the two satellite images was comparable, when the difference of GSD is taken into account.

WE‐EF‐303‐05: Development and Commissioning of Real‐Time Imaging Function for Respiratory‐Gated Spot‐Scanning Proton Beam Therapy

Purpose:To realize real‐time‐image gated proton beam therapy (RGPT) for treating mobile tumors.Methods:The rotating gantry of spot scanning proton beam therapy has been designed to equip two x‐ray fluoroscopy devices that enable real‐time imaging of the internal fiducial markers during respiration. Three‐dimensional position of the fiducial marker located near the tumor can be calculated from the fluoroscopic images obtained from orthogonal directions and therapeutic beam is gated only when the fiducial marker is within the predefined gating window. Image acquisition rate can be selected from discrete value ranging from 0.1 Hz to 30 Hz. In order to confirm the effectiveness of RGPT and apply it clinically, clinical commissioning was conducted. Commissioning tests were categorized to main three parts including geometric accuracy, temporal accuracy and dosimetric evaluation.Results:Developed real‐time imaging function has been installed and its basic performances have been confirmed. In the evaluation of geometric accuracy, coincidence of three‐dimensional treatment room coordinate system and imaging coordinate system was confirmed to be less than 1 mm. Fiducial markers (gold sphere and coil) were able to be tracked in simulated clinical condition using an anthropomorphic chest phantom. In the evaluation of temporal accuracy, latency from image acquisition to gate on/off signal was about 60 msec in typical case. In dosimetric evaluation, treatment beam characteristics including beam irradiation position and dose output were stable in gated irradiation. Homogeneity indices to the mobile target were 0.99 (static), 0.89 (w/o gating, motion is parallel to direction of scan), 0.75 (w/o gating, perpendicular), 0.98 (w/ gating, parallel) and 0.93 (w/ gating, perpendicular). Dose homogeneity to the mobile target can be maintained in RGPT.Conclusion:Real‐time imaging function utilizing x‐ray fluoroscopy has been developed and commissioned successfully in order to realize RGPT.Funding Support: This research was partially supported by Japan Society for the Promotion of Science (JSPS) through the FIRST Program. Conflict of Interest: Prof. Shirato has research fund from Hitachi Ltd, Mitsubishi Heavy Industries Ltd and Shimadzu Corporation.

SU-E-T-291: Dosimetric Accuracy of Multitarget Single Isocenter Radiosurgery

Purpose: To evaluate the accuracy of single-isocenter multiple-target VMAT radiosurgery (SIMT-VMAT-SRS) by analysis of pre-treatment verification measurements. Methods: Our QA procedure used a phantom having a coronal plane for EDR2 film and a 0.125 cm3 ionization chamber. Film measurements were obtained for the largest and smallest targets for each plan. An ionization chamber measurement (ICM) was obtained for sufficiently large targets. Films were converted to dose using a patient-specific calibration curve and compared to treatment planning system calculations. Alignment error was estimated using image registration. The gamma index was calculated for 3%/3 and 3%/1 mm criteria. The median dose in the target region and, for plans having an ICM, the average dose in the central 5 mm was calculated. Results: The average equivalent target diameter of the 48 targets was 15 mm (3–43 mm). Twenty of the 24 plans had an ICM for the plan corresponding to the largest target (diameter 11–43 mm) with a mean ratio of chamber reading to expected dose (ED) and the mean ratio of film to ED (averaged over the central 5 mm) was 1.001 (0.025 SD) and 1.000 (0.029 SD), respectively. For all plans, the mean film to ED (from the median dose in the target region) was 0.997 (0.027 SD). The mean registration vector was (0.15,0.29) mm, with an average magnitude of 0.96 mm. Before (after) registration, the average fraction of pixels having gamma < 1 was 99.3% (99.6%) and 89.1% (97.6%) for 3%/3mm and 3%/1mm, respectively. Conclusion: Our results demonstrate dosimetric accuracy of SIMT-VMAT-SRS for targets as small as 3 mm. Film dosimetry provides accurate assessment of the absolute dose delivered to targets too small for an ionization chamber measurement; however, the relatively large registration vector indicates that image-guidance should replace laser-based setup for patient-specific evaluation of geometric accuracy.

Geometric Accuracy Evaluation of Fabricated Parts by Additive Manufacturing toward Parallel Fabrication

Most rapid prototyping models are fabricated by additive manufacturing (AM) devices, which are usually called as 3D-printers. The AM models are expected to be used as practical parts for small batch manufacturing and maintenance parts supply. The main problem of AM for practical parts depends on processing accuracy and productivity. To compete with these problems, the parallel fabrication is considered. In this paper, after the concept of the parallel fabrication is introduced, the geometric accuracy of AM parts is evaluated and discussed from viewpoints of shape and processing. Two primitive shapes, which are a cube and a cylinder, are chosen as evaluation objects. These models are fabricated by two different type AM processing, which are Stereo Lithography (SL) and Fused Deposition Modeling (FDM). The geometry of objects is measured by a contact type 3D measurement system. As a result, characteristics of geometric error, which depend on shape features and AM processing, were found. The design guideline for contact surfaces between segmented parts is discussed.