bluuebunny/crossref_metadata_2025_split huggingface dataset:
An algorithm to extract three‐dimensional motion by marker tracking in the kV projections from an on‐board imager: four‐dimensional cone‐beam CT and tumor tracking implications
Authors: Ali Imad , Alsbou Nesreen , Herman Terence , Ahmad Salahuddin 
Published: February 2017

The purpose of this work is to extract three‐dimensional (3D) motion trajectories of internal implanted and external skin‐attached markers from kV cone‐beam projections and reduce image artifact from patient motion in cone‐beam computed tomography (CBCT) from on‐board imager. Cone beam radiographic projections were acquired for a mobile phantom and liver patients with internal implanted and external skin‐attached markers. An algorithm was developed to automatically find the positions of the markers in the projections. It uses normalized cross‐correlation between a template image of a metal seed marker and the projections to find the marker position. From these positions and time‐tagged angular views, the marker 3D motion trajectory was obtained over a time interval of nearly one minute, which is the time required for scanning. This marker trajectory was used to remap the pixels of the projections to eliminate motion. Then, the motion‐corrected projections were used to reconstruct CBCT. An algorithm was developed to extract 3D motion trajectories of internal and external markers from cone‐beam projections using a kV monoscopic on‐board imager. This algorithm was tested and validated using a mobile phantom and patients with liver masses that had radio‐markers implanted in the tumor and attached to the skin. The extracted motion trajectories were used to investigate motion correlation between internal and external markers in liver patients. Image artifacts from respiratory motion were reduced in CBCT reconstructed from cone‐beam projections that were preprocessed to remove motion shifts obtained from marker tracking. With this method, motion‐related image artifacts such as blurring and spatial distortion were reduced, and contrast and position resolutions were improved significantly in CBCT reconstructed from motion‐corrected projections. Furthermore, correlated internal and external marker 3D‐motion tracks obtained from the kV projections might be useful for 4DCBCT, beam gating and tumor motion monitoring or tracking.PACS numbers: 87.57.Q, 87.57.C‐
An image quality comparison study between XVI and OBI CBCT systems
Authors: Kamath Srijit , Song William , Chvetsov Alexei , Ozawa Shuichi , Lu Haibin , Samant Sanjiv , Liu Chihray , Li Jonathan G. , Palta Jatinder R. 
Published: February 2017

The purpose of this study is to evaluate and compare image quality characteristics for two commonly used and commercially available CBCT systems: the X‐ray Volumetric Imager and the On‐Board Imager. A commonly used CATPHAN image quality phantom was used to measure various image quality parameters, namely, pixel value stability and accuracy, noise, contrast to noise ratio (CNR), high‐contrast resolution, low contrast resolution and image uniformity. For the XVI unit, we evaluated the image quality for four manufacturer‐supplied protocols as a function of mAs. For the OBI unit, we did the same for the full‐fan and half‐fan scanning modes, which were respectively used with the full bow‐tie and half bow‐tie filters. For XVI, the mean pixel values of regions of interest were found to generally decrease with increasing mAs for all protocols, while they were relatively stable with mAs for OBI. Noise was slightly lower on XVI and was seen to decrease with increasing mAs, while CNR increased with mAs for both systems. For XVI and OBI, the high‐contrast resolution was approximately limited by the pixel resolution of the reconstructed image. On OBI images, up to 6 and 5 discs of 1% and 0.5% contrast, respectively, were visible for a high mAs setting using the full‐fan mode, while none of the discs were clearly visible on the XVI images for various mAs settings when the medium resolution reconstruction was used. In conclusion, image quality parameters for XVI and OBI have been quantified and compared for clinical protocols under various mAs settings. These results need to be viewed in the context of a recent study that reported the dose‐mAs relationship for the two systems and found that OBI generally delivered higher imaging doses than XVI.(1)PACS numbers: 85.57.C‐, 85.57.cj, 85.57.cm, 85.57.cf
Evaluation of stereotactic radiosurgery conformity indices for 170 target volumes in patients with brain metastases
Authors: Stanley Julia , Breitman Karen , Dunscombe Peter , Spencer David P. , Lau Harold 
Published: February 2017

A database of clinically approved stereotactic radiosurgery treatment plans was created. One hundred and seventy targets in the database were then retrospectively evaluated using conformity indices suggested by RTOG, SALT‐Lomax and Paddick. Relationships between the three alternative conformity indices were determined. The Paddick index combines the information provided by the RTOG and SALT‐Lomax indices into a single index. The variation in the geometric overlap ratio, which is related to the SALT‐Lomax index, was found to be not clinically relevant for our cohort of patients, and thus the Paddick and RTOG indices can be directly related. It was found that access to a dose volume histogram or dose distribution for a treatment plan renders the RTOG conformity index sufficient for plan quality evaluation.PACS number: 87.53.Ly
Dosimetric impact of density variations in Solid Water 457 water‐equivalent slabs
Authors: Litzenberg Dale W. , Amro Hanan , Prisciandaro Joann I. , Acosta Eduardo , Gallagher Ian , Roberts Don A. 
Published: February 2017

The purpose of this study was to determine the dosimetric impact of density variations observed in water‐equivalent solid slabs. Measurements were performed using two water‐equivalent slabs, one being 4 cm think and the other 5 cm thick. The location and extent of density variations were determined by computed tomography (CT) scans. Additional imaging measurements were made with an amorphous silicon megavoltage portal imaging device and an ultrasound unit. Dosimetric measurements were conducted with a 2D ion chamber array, and a scanned diode in water. Additional measurements and calculations were made of small rectilinear void inhomogeneities formed with water‐equivalent slabs, using a 2D ion chamber array and the convolution superposition algorithm. Two general types of density variation features were observed on CT images: 1) regions of many centimeters across, but typically only a few millimeters thick, with electron densities a few percent lower than the bulk material, and 2) cylindrical regions roughly 0.2 cm in diameter and up to 20 cm long with electron densities up to 5% lower than the surrounding material. The density variations were not visible on kilovoltage, megavoltage or ultrasound images. The dosimetric impact of the density variations were not detectable to within 0.1% using the 2D ion chamber array or the scanning photon diode at distances 0.4 cm to 2 cm beyond the features. High‐resolution dosimetric calculations using the convolution–superposition algorithm with density corrections enabled on CT‐based datasets showed no discernable dosimetric impact. Calculations and measurements on simulated voids place the upper limit on possible dosimetric variations from observed density variations at much less than 0.6%. CT imaging of water‐equivalent slabs may reveal density variations which are otherwise unobserved with kV, MV, or ultrasound imaging. No dosimetric impact from these features was measureable with an ion chamber array or scanned photon diode. Consequently, they were determined to be acceptable for all clinical use.PACS numbers: 87.55.km, 87.55.Qr
Calculation of exit dose for conformal and dynamically‐wedged fields, based on water‐equivalent path length measured with an amorphous silicon electronic portal imaging device
Authors: Kavuma Awusi , Glegg Martin , Metwaly Mohamed , Currie Garry , Elliott Alex 
Published: February 2017

In this study, we use the quadratic calibration method (QCM), in which an EPID image is converted into a matrix of equivalent path lengths (EPLs) and, therefore, exit doses, so as to model doses in conformal and enhanced dynamic wedge (EDW) fields. The QCM involves acquiring series of EPID images at a reference field size for different thicknesses of homogeneous solid water blocks. From these, a set of coefficients is established that is used to compute the EPL of any other irradiated material. To determine the EPL, the irradiated area must be known in order to establish the appropriate scatter correction. A method was devised for the automatic calculation of areas from the EPID image that facilitated the calculation of EPL for any field and exit dose. For EDW fields, the fitting coefficients were modified by utilizing the linac manufacturer's golden segmented treatment tables (GSTT) methodology and MU fraction model. The nonlinear response of the EPL with lower monitor units (MUs) was investigated and slight modification of the algorithm performed to account for this. The method permits 2D dose distributions at the exit of phantom or patient to be generated by relating the EPL with an appropriate depth dose table. The results indicate that the inclusion of MU correction improved the EPL determination. The irradiated field areas can be accurately determined from EPID images to within uncertainty. Cross‐plane profiles and 2D dose distributions of EPID predicted doses were compared with those calculated with the Eclipse treatment planning system (TPS) and those measured directly with MapCHECK 2 device. Comparison of the 2D EPID dose maps to those from TPS and MapCHECK shows that more than 90% of all points passed the gamma index acceptance criteria of 3% dose difference and 3 mm distance to agreement (DTA), for both conformal and EDW study cases. We conclude that the EPID QCM is an accurate and convenient method for in vivo dosimetry and may, therefore, complement existing techniques.PACS numbers: 87.50.ct, 87.55 D
Feasibility study of performing IGRT system daily QA using a commercial QA device
Authors: L.Peng Jean , Kahler Darren , Li Jonathan G. , J.Amdur Robert , Vanek Kenneth N. , Liu Chihray 
Published: February 2017

The purpose of this study was to investigate the feasibility of using a single QA device for comprehensive, efficient daily QA of a linear accelerator (Linac) and three image‐guided stereotactic positioning systems (IGSPSs). The Sun Nuclear Daily QA 3 (DQA3) device was used to perform daily dosimetry and mechanical accuracy tests for an Elekta Linac, as well as daily image geometric and isocenter coincidence accuracy tests for three IGSPSs: the AlignRT surface imaging system; the frameless SonArray optical tracking System (FSA) and the Elekta kV CBCT. The DQA3 can also be used for couch positioning, repositioning, and rotational tests during the monthly QA. Based on phantom imaging, the Linac coordinate system determined using AlignRT was within 0.7 mm/0.6° of that of the CBCT system. The difference is attributable to the different calibration methods that are utilized for these two systems. The laser alignment was within 0.5 mm of the isocenter location determined with the three IGSPSs. The ODI constancy was . For gantry and table angles of 0°, the mean isocenter displacement vectors determined using the three systems were within 0.7 mm and 0.6° of one another. Isocenter rotational offsets measured with the systems were all . For photon and electron beams tested over a period of eight months, the output was verified to remain within 2%, energy variations were within 2%, and the symmetry and flatness were within 1%. The field size and light‐radiation coincidence were within 1mm . For dosimetry reproducibility, the standard deviation was within 0.2% for all tests and all energies, except for photon energy variation which was 0.6%. The total measurement time for all tasks took less than 15 minutes per QA session compared to 40 minutes with our previous procedure, which utilized an individual QA device for each IGSPS. The DQA3 can be used for accurate and efficient Linac and IGSPS daily QA. It shortens QA device setup time, eliminates errors introduced by changing phantoms to perform different tests, and streamlines the task of performing dosimetric checks.PACS number: 87.56.Fc
Validation of an electron Monte Carlo dose calculation algorithm in the presence of heterogeneities using EGSnrc and radiochromic film measurements
Authors: Aubry Jean‐François , Bouchard Hugo , Bessières Igor , Lacroix Frédéric 
Published: February 2017

The purpose of this study is to validate Eclipse's electron Monte Carlo algorithm (eMC) in heterogeneous phantoms using radiochromic films and EGSnrc as a reference Monte Carlo algorithm. Four heterogeneous phantoms are used in this study. Radiochromic films are inserted in these phantoms, including in heterogeneous media, and the measured relative dose distributions are compared to eMC calculations. Phantoms A, B, and C contain 1D heterogeneities, built with layers of lung‐ (phantom A) and bone‐ (phantoms B and C) equivalent materials sandwiched in Plastic Water. Phantom D is a thorax‐anthropomorphic phantom with 2D lung heterogeneities. Electron beams of 6, 9, 12 and 18 MeV from a Varian Clinac 2100 are delivered to these phantoms with a applicator. Monte Carlo simulations with an independent algorithm (EGSnrc) are also used as a reference tool for two purposes: (1) as a second validation of the eMC dose calculations, and (2) to calculate the stopping power ratio between radiochromic films and bone medium, when dose is measured inside the heterogeneity. Percent depth dose (PDD) film measurements and eMC calculations agree within 2% or 3 mm for phantom A, and within 3% or 3 mm for phantoms B and C for almost all beam energies. One exception is observed with phantom B and the 6 MeV, where measured PDDs and those calculated with eMC differ by up to 4 mm. Gamma analysis of the measured and calculated 2D dose distributions in phantom D agree with criteria of 3%, 3 mm for 9, 12, and 18 MeV beams, and criteria of 5%, 3 mm for the 6 MeV beam. Dose calculations in heterogeneous media with eMC agree within 3% or 3 mm with radiochromic film measurements. Six (6) MeV beams are not modeled as accurately as other beam energies. The eMC algorithm is suitable for clinical dose calculations involving lung and bone.PACS numbers: 87.10.Rt, 87.55.km
A method to enhance spatial resolution of a 2D ion chamber array for quality control of MLC
Authors: Moreno Rogelio Díaz , Venencia Daniel , Garrigo Edgardo , Pipman Yakov 
Published: February 2017

This work introduces a new method for verifying MLC leaf positions with enough spatial resolution to replace film‐based methods in performing QA tests. It is implemented on a 2D ion chamber array, and it is based on the principle of varying signal response of a volumetric detector to partial irradiation. A PTW 2D‐ARRAY seven29 (PTW‐729 2D) array was used to assess a Siemens OPTIFOCUS MLC. Partial volume response curves for chambers in the array were obtained by irradiating them with the leaves of the MLC, progressively covering varying portions of the chambers correlated with the leaf positions. The readings from the array's chambers are processed with an in‐house program; it generates a reference response that translates readings into leaf positions. This principle allows discriminating errors in pairs of opposing leaves that could combine to cancel their detection with other tools.Patterns of leaf positions, similar to the Bayouth test but with different, purposefully introduced errors, were generated and used to test the effectiveness of the method. The same patterns were exposed on radiographic film and analyzed with the RIT software for validation. For four test patterns with a total of 100 errors of , and , all were correctly determined with the proposed method. The analysis of the same pattern with film using the Bayouth routine in the RIT software resulted in either somewhat low true positives combined with a large fraction of false positives, or a low true positive rate with a low false positive ratio, the results being significantly affected by the threshold selected for the analysis.This method provides an effective, easy to use tool for quantitative MLC QA assessment, with excellent spatial resolution. It can be easily applied to other 2D arrays, as long as they exhibit a partial volume detector response.PACS number: 87.55.Qr
Motion artifacts occurring at the lung/diaphragm interface using 4D CT attenuation correction of 4D PET scans
Authors: Killoran Joseph H. , Gerbaudo Victor H , Mamede Marcelo , Ionascu Dan , Park Sang‐June , Berbeco Ross 
Published: February 2017

For PET/CT, fast CT acquisition time can lead to errors in attenuation correction, particularly at the lung/diaphragm interface. Gated 4D PET can reduce motion artifacts, though residual artifacts may persist depending on the CT dataset used for attenuation correction. We performed phantom studies to evaluate 4D PET images of targets near a density interface using three different methods for attenuation correction: a single 3D CT (3D CTAC), an averaged 4D CT (CINE CTAC), and a fully phase matched 4D CT (4D CTAC). A phantom was designed with two density regions corresponding to diaphragm and lung. An 8 mL sphere phantom loaded with 18F‐FDG was used to represent a lung tumor and background FDG included at an 8:1 ratio. Motion patterns of and were used for dynamic studies. Image data was acquired using a GE Discovery DVCT‐PET/CT scanner. Attenuation correction methods were compared based on normalized recovery coefficient (NRC), as well as a novel quantity “fixed activity volume” (FAV) introduced in our report. Image metrics were compared to those determined from a 3D PET scan with no motion present (3D STATIC). Values of FAV and NRC showed significant variation over the motion cycle when corrected by 3D CTAC images. 4D CTAC‐ and CINE CTAC–corrected PET images reduced these motion artifacts. The amount of artifact reduction is greater when the target is surrounded by lower density material and when motion was based on . 4D CTAC reduced artifacts more than CINE CTAC for most scenarios. For a target surrounded by water equivalent material, there was no advantage to 4D CTAC over CINE CTAC when using the motion pattern. Attenuation correction using both 4D CTAC or CINE CTAC can reduce motion artifacts in regions that include a tissue interface such as the lung/diaphragm border. 4D CTAC is more effective than CINE CTAC at reducing artifacts in some, but not all, scenarios.PACS numbers: 87.57.qp, 87.57.cp
Deformable registration using edge‐preserving scale space for adaptive image‐guided radiation therapy
Authors: Li Dengwang , Wang Hongjun , Yin Yong , Wang Xiuying 
Published: February 2017

Incorporating of daily cone‐beam computer tomography (CBCT) image into online radiation therapy process can achieve adaptive image‐guided radiation therapy (AIGRT). Registration of planning CT (PCT) and daily CBCT are the key issues in this process. In our work, a new multiscale deformable registration method is proposed by combining edge‐preserving scale space with the multilevel free‐form deformation (FFD) grids for CBCT‐based AIGRT system. The edge‐preserving scale space, which is able to select edges and contours of images according to their geometric size, is derived from the total variation model with the L1 norm (TV‐L1). At each scale, despite the noise and contrast resolution differences between the PCT and CBCT, the selected edges and contours are sufficiently strong to drive the deformation using the FFD grid, and the edge‐preserving property ensures more meaningful spatial information for mutual information (MI)‐based registration. At last, the deformation fields are gained by a coarse to fine manner. Furthermore, in consideration of clinical application we designed an optimal estimation of the TV‐L1 parameters by minimizing the defined offset function for automated registration.Six types of patients are studied in our work, including rectum, prostate, lung, H&N (head and neck), breast, and chest cancer patients. The experiment results demonstrate the significance of the proposed method both quantitatively with ground truth known and qualitatively with ground truth unknown. The applications for AIGRT, including adaptive deformable recontouring and redosing, and DVH (dose volume histogram) analysis in the course of radiation therapy are also studied.PACS numbers: 87.57.Gg, 87.57.Ce, 87.62.+n
Establishment of air kerma reference standard for low dose rate Cs‐137 brachytherapy sources
Authors: Sharma Sunil Dutt , Kumar Sudhir , Srinivasan P. , Chourasiya G. 
Published: February 2017

A guarded cylindrical graphite ionization chamber of nominal volume was designed and fabricated for use as a reference standard for low‐dose rate brachytherapy sources. The air kerma calibration coefficient of this ionization chamber was estimated analytically using Burlin's general cavity theory, as well as by the Monte Carlo simulation and validated experimentally using Amersham CDCS‐J‐type reference source. In the analytical method, the was calculated for 662 keV gamma rays of brachytherapy source. In the Monte Carlo method, the geometry of the measurement setup and physics‐related input data of the source and the surrounding material were simulated using the Monte Carlo N‐Particle code. The photon energy fluence was used to arrive at the reference air kerma rate (RAKR) using mass energy absorption coefficient. The energy deposition rates were used to simulate the value of charge rate in the ionization chamber, and the was determined. The analytical and Monte Carlo values of of the cylindrical graphite ionization chamber for brachytherapy source are in agreement within 1.07%. The deviation of analytical and Monte Carlo values from experimental values of is 0.36% and 0.72%, respectively. This agreement validates the analytical value, and establishes this chamber as a reference standard for RAKR or AKS measurement of brachytherapy sources.PACS numbers: 87.53.Bn, 87.53.Jw, 87.56.bg, 87.55.Qr
Energy absorption buildup factors of human organs and tissues at energies and penetration depths relevant for radiotherapy and diagnostics
Authors: Manohara S. R. , Hanagodimath S. M. , Gerward L. 
Published: February 2017

Energy absorption geometric progression (GP) fitting parameters and the corresponding buildup factors have been computed for human organs and tissues, such as adipose tissue, blood (whole), cortical bone, brain (grey/white matter), breast tissue, eye lens, lung tissue, skeletal muscle, ovary, testis, soft tissue, and soft tissue (4‐component), for the photon energy range 0.015–15 MeV and for penetration depths up to 40 mfp (mean free path). The chemical composition of human organs and tissues is seen to influence the energy absorption buildup factors. It is also found that the buildup factor of human organs and tissues changes significantly with the change of incident photon energy and effective atomic number, . These changes are due to the dominance of different photon interaction processes in different energy regions and different chemical compositions of human organs and tissues.With the proper knowledge of buildup factors of human organs and tissues, energy absorption in the human body can be carefully controlled. The present results will help in estimating safe dose levels for radiotherapy patients and also useful in diagnostics and dosimetry. The tissue‐equivalent materials for skeletal muscle, adipose tissue, cortical bone, and lung tissue are also discussed. It is observed that water and MS20 are good tissue equivalent materials for skeletal muscle in the extended energy range.PACS numbers: 32.80‐t, 87.53‐j, 78.70‐g, 78.70‐Ck