bluuebunny/crossref_metadata_2025_split huggingface dataset:
Technical Note: RabbitCT—an open platform for benchmarking 3D cone‐beam reconstruction algorithmsa)
Authors: Rohkohl C. , Keck B. , Hofmann H. G. , Hornegger J. 
Published: August 2009

Purpose:Fast 3D cone beam reconstruction is mandatory for many clinical workflows. For that reason, researchers and industry work hard on hardware‐optimized 3D reconstruction. Backprojection is a major component of many reconstruction algorithms that require a projection of each voxel onto the projection data, including data interpolation, before updating the voxel value. This step is the bottleneck of most reconstruction algorithms and the focus of optimization in recent publications. A crucial limitation, however, of these publications is that the presented results are not comparable to each other. This is mainly due to variations in data acquisitions, preprocessing, and chosen geometries and the lack of a common publicly available test dataset. The authors provide such a standardized dataset that allows for substantial comparison of hardware accelerated backprojection methods.Methods:They developed an open platform RabbitCT (www.rabbitCT.com) for worldwide comparison in backprojection performance and ranking on different architectures using a specific high resolution C‐arm CT dataset of a rabbit. This includes a sophisticated benchmark interface, a prototype implementation in C++, and image quality measures.Results:At the time of writing, six backprojection implementations are already listed on the website. Optimizations include multithreading using Intel threading building blocks and OpenMP, vectorization using SSE, and computation on the GPU usingCUDA 2.0.Conclusions:There is a need for objectively comparing backprojection implementations for reconstruction algorithms. RabbitCT aims to provide a solution to this problem by offering an open platform with fair chances for all participants. The authors are looking forward to a growing community and await feedback regarding future evaluations of novel software‐ and hardware‐based acceleration schemes.
Megavoltage planar and cone‐beam imaging with low‐ targets: Dependence of image quality improvement on beam energy and patient separation
Authors: Robar James L. , Connell Tanner , Huang Weihong , Kelly Robin G. 
Published: August 2009

Purpose:The purpose of this study is to investigate the improvement of megavoltage planar and cone‐beam CT (CBCT) image quality with the use of low atomic number external targets in the linear accelerator.Methods:In this investigation, two experimental megavoltage imaging beams were generated by using either 3.5 or electrons incident on aluminum targets installed above the level of the carousel in a linear accelerator (2100EX, Varian Medical, Inc., Palo Alto, CA). Images were acquired using an amorphous silicon detector panel. Contrast‐to‐noise ratio (CNR) in planar and CBCT images was measured as a function of dose and a comparison was made between the imaging beams and the standard therapy beam. Phantoms of variable diameter were used to examine the loss of contrast due to beam hardening. Porcine imaging was conducted to examine qualitatively the advantages of the low‐ target approach in CBCT.Results:In CBCT imaging CNR increases by factors as high as 2.4 and 4.3 for the 7.0 and beams, respectively, compared to images acquired with . Similar factors of improvement are observed in planar imaging. For the imaging beams, beam hardening causes a significant loss of the contrast advantage with increasing phantom diameter; however, for the beam and a phantom diameter of , a contrast advantage remains, with increases of contrast by factors of 1.5 and 3.4 over for bone and lung inhale regions, respectively. The spatial resolution is improved slightly in CBCT images for the imaging beams. CBCT images of a porcine cranium demonstrate qualitatively the advantages of the low‐ target approach, showing greater contrast between tissues and improved visibility of fine detail.Conclusions:The use of low‐ external targets in the linear accelerator improves megavoltage planar and CBCT image quality significantly. CNR may be increased by a factor of 4 or greater. Improvement of the spatial resolution is also apparent.
Multiple scattering of 13 and 20 MeV electrons by thin foils: A Monte Carlo study with GEANT, Geant4, and PENELOPE
Authors: Vilches M. , García‐Pareja S. , Guerrero R. , Anguiano M. , Lallena A. M. 
Published: August 2009

Purpose:In this work, recent results from experiments and simulations (with EGSnrc) performed by Rosset al. [Med. Phys. 35, 4121–4131 (2008)] on electron scattering by foils of different materials and thicknesses are compared to those obtained using several Monte Carlo codes.Methods:Three codes have been used: GEANT (version 3.21), Geant4 (version 9.1, patch03), and PENELOPE (version 2006). In the case of PENELOPE, mixed and fully detailed simulations have been carried out.Results:Transverse dose distributions in air have been obtained in order to compare with measurements. The detailed PENELOPE simulations show excellent agreement with experiment. The calculations performed with GEANT and PENELOPE (mixed) agree with experiment within 3% except for the Be foil. In the case of Geant4, the distributions are 5% narrower compared to the experimental ones, though the agreement is very good for the Be foil. Transverse dose distribution in water obtained with PENELOPE (mixed) is 4% wider than those calculated by Rosset al. using EGSnrc and is 1% narrower than the transverse dose distributions in air, as considered in the experiment.Conclusions:All the codes give a reasonable agreement (within 5%) with the experimental results for all the material and thicknesses studied.
A CT‐based analytical dose calculation method for HDR brachytherapy
Authors: Poon Emily , Verhaegen Frank 
Published: August 2009

Purpose:This article presents an analytical dose calculation method for high‐dose‐rate brachytherapy, taking into account the effects of inhomogeneities and reduced photon backscatter near the skin. The adequacy of the Task Group 43 (TG‐43) two‐dimensional formalism for treatment planning is also assessed.Methods:The proposed method uses material composition and density data derived from computed tomography images. The primary and scatter dose distributions for each dwell position are calculated first as if the patient is an infinite water phantom. This is done using either TG‐43 or a database of Monte Carlo (MC) dose distributions. The latter can be used to account for the effects of shielding in water. Subsequently, corrections for photon attenuation, scatter, and spectral variations along medium‐ or low‐ inhomogeneities are made according to the radiological paths determined by ray tracing. The scatter dose is then scaled by a correction factor that depends on the distances between the point of interest, the body contour, and the source position. Dose calculations are done for phantoms with tissue and lead inserts, as well as patient plans for head‐and‐neck, esophagus, and MammoSite balloon breast brachytherapy treatments. Gamma indices are evaluated using a dose‐difference criterion of 3% and a distance‐to‐agreement criterion of 2 mm. PTRAN_CT MC calculations are used as the reference dose distributions.Results:For the phantom with tissue and lead inserts, the percentages of the voxels of interest passing the gamma criteria are 100% for the analytical calculation and 91% for TG‐43. For the breast patient plan, TG‐43 overestimates the target volume receiving the prescribed dose by 4% and the dose to the hottest of the skin by 9%, whereas the analytical and MC results agree within 0.4%. are 100% and 48% for the analytical and TG‐43 calculations, respectively. For the head‐and‐neck and esophagus patient plans, are for both calculation methods.Conclusions:A correction‐based dose calculation method has been validated for HDR brachytherapy. Its high calculation efficiency makes it feasible for use in treatment planning. Because tissue inhomogeneity effects are small and primary dose predominates in the near‐source region, TG‐43 is adequate for target dose estimation provided shielding and contrast solution are not used.
Dual resolution cone beam breast CT: A feasibility study
Authors: Chen Lingyun , Shen Youtao , Lai Chao‐Jen , Han Tao , Zhong Yuncheng , Ge Shuaiping , Liu Xinming , Wang Tianpeng , Yang Wei T. , Whitman Gary J. , Shaw Chris C. 
Published: August 2009

Purpose:In this study, the authors investigated the feasibility of a dual resolution volume‐of‐interest (VOI) cone beam breast CT technique and compared two implementation approaches in terms of dose saving and scatter reduction.Methods:With this technique, a lead VOI mask with an opening is inserted between the x‐ray source and the breast to deliver x‐ray exposure to the VOI while blocking x rays outside the VOI. A CCD detector is used to collect the high resolution projection data of the VOI. Low resolution cone beam CT (CBCT) images of the entire breast, acquired with a flat panel (FP) detector, were used to calculate the projection data outside the VOI with the ray‐tracing reprojection method. The Feldkamp–Davis–Kress filtered backprojection algorithm was used to reconstruct the dual resolution 3D images. Breast phantoms with and smaller microcalcifications (MCs) were imaged with both FP and FP‐CCD dual resolution CBCT systems, respectively. Two approaches of implementing the dual resolution technique, breast‐centered approach and VOI‐centered approach, were investigated and evaluated for dose saving and scatter reduction with Monte Carlo simulation using a GEANT4 package.Results:The results showed that the breast‐centered approach saved more breast absorbed dose than did VOI‐centered approach with similar scatter reduction. The MCs in fatty breast phantom, which were invisible with FP CBCT scan, became visible with the FP‐CCD dual resolution CBCT scan.Conclusions:These results indicate potential improvement of the image quality inside the VOI with reduced breast dose both inside and outside the VOI.
From the limits of the classical model of sensitometric curves to a realistic model based on the percolation theory for GafChromic™ EBT films
Authors: del Moral F. , Vázquez J. A. , Ferrero J. J. , Willisch P. , Ramírez R. D. , Teijeiro A. , Medina A. López , Andrade B. , Vázquez J. , Salvador F. , Medal D. , Salgado M. , Muñoz V. 
Published: August 2009

Purpose:Modern radiotherapy uses complex treatments that necessitate more complex quality assurance procedures. As a continuous medium, GafChromic EBT films offer suitable features for such verification. However, its sensitometric curve is not fully understood in terms of classical theoretical models. In fact, measured optical densities and those predicted by the classical models differ significantly. This difference increases systematically with wider dose ranges. Thus, achieving the accuracy required for intensity‐modulated radiotherapy (IMRT) by classical methods is not possible, plecluding their use. As a result, experimental parametrizations, such as polynomial fits, are replacing phenomenological expressions in modern investigations. This article focuses on identifying new theoretical ways to describe sensitometric curves and on evaluating the quality of fit for experimental data based on four proposed models.Methods:A whole mathematical formalism starting with a geometrical version of the classical theory is used to develop new expressions for the sensitometric curves. General results from the percolation theory are also used. A flat‐bed‐scanner‐based method was chosen for the film analysis. Different tests were performed, such as consistency of the numeric results for the proposed model and double examination using data from independent researchers.Results:Results show that the percolation‐theory‐based model provides the best theoretical explanation for the sensitometric behavior of GafChromic films. The different sizes of active centers or monomer crystals of the film are the basis of this model, allowing acquisition of information about the internal structure of the films. Values for the mean size of the active centers were obtained in accordance with technical specifications. In this model, the dynamics of the interaction between the active centers of GafChromic film and radiation is also characterized by means of its interaction cross‐section value.Conclusions:The percolation model fulfills the accuracy requirements for quality‐control procedures when large ranges of doses are used and offers a physical explanation for the film response.
Matching extended‐SSD electron beams to multileaf collimated photon beams in the treatment of head and neck cancer
Authors: Steel Jared , Stewart Allan , Satory Philip 
Published: August 2009

Purpose:Matching the penumbra of a electron beam to the penumbra of a photon beam is a dose optimization challenge, especially when the electron beam is applied from an extended source‐to‐surface distance (SSD), as in the case of some head and neck treatments. Traditionally low melting point alloy blocks have been used to define the photon beam shielding over the spinal cord region. However, these are inherently time consuming to construct and employ in the clinical situation. Multileaf collimators (MLCs) provide a fast and reproducible shielding option but generate geometrically nonconformal approximations to the desired beam edge definition. The effects of substituting Cerrobend® for the MLC shielding mode in the context of beam matching with extended‐SSD electron beams are the subject of this investigation.Methods:Relative dose beam data from a Varian EX 2100 linear accelerator were acquired in a water tank under the electron beam at both standard and extended‐SSD and under the photon beam defined by Cerrobend® and a number of MLC stepping regimes. The effect of increasing the electron beam SSD on the beam penumbra was assessed. MLC stepping was also assessed in terms of the effects on both the mean photon beam penumbra and the intraleaf dose‐profile nonuniformity relative to the MLC midleaf. Computational techniques were used to combine the beam data so as to simulate composite relative dosimetry in the water tank, allowing fine control of beam abutment gap variation. Idealized volumetric dosimetry was generated based on the percentage depth‐dose data for the beam modes and the abutment geometries involved. Comparison was made between each composite dosimetry dataset and the relevant ideal dosimetry dataset by way of subtraction.Results:Weighted dose‐difference volume histograms (DDVHs) were produced, and these, in turn, summed to provide an overall dosimetry score for each abutment and shielding type/angle combination. Increasing the electron beam SSD increased the penumbra width (defined as the lateral distance of the 80% and 20% isodose contours) by at the depths of . Mean photon beam penumbra width increased with increased MLC stepping, and the mean MLC penumbra was times greater than that across the corresponding Cerrobend® shielding. Intraleaf dose discrepancy in the direction orthogonal to the beam edge also increased with MLC stepping.Conclusions:The weighted DDVH comparison techniques allowed the composite dosimetry resulting from the interplay of the abovementioned variables to be ranked. The MLC dosimetry ranked as good or better than that resulting from beam matching with Cerrobend® for all except large field overlaps ( gap). The results for the linear‐weighted DDVH comparison suggest that optimal MLC abutment dosimetry results from an optical surface gap of around . Furthermore, this appears reasonably lenient to abutment gap variation, such as that arising from uncertainty in beam markup or other setup errors.
Accelerated ray tracing for radiotherapy dose calculations on a GPU
Authors: de Greef M. , Crezee J. , van Eijk J. C. , Pool R. , Bel A. 
Published: August 2009

Purpose:The graphical processing unit (GPU) on modern graphics cards offers the possibility of accelerating arithmetically intensive tasks. By splitting the work into a large number of independent jobs, order‐of‐magnitude speedups are reported. In this article, the possible speedup of PLATO's ray tracing algorithm for dose calculations using a GPU is investigated.Methods:A GPU version of the ray tracing algorithm was implemented using NVIDIA's CUDA, which extends the standard C language with functionality to program graphics cards. The developed algorithm was compared based on the accuracy and speed to a multithreaded version of the PLATO ray tracing algorithm. This comparison was performed for three test geometries, a phantom and two radiotherapy planning CT datasets (a pelvic and a head‐and‐neck case). For each geometry, four different source positions were evaluated. In addition to this, for the head‐and‐neck case also a vertex field was evaluated.Results:The GPU algorithm was proven to be more accurate than the PLATO algorithm by elimination of the look‐up table for indices that introduces discretization errors in the reference algorithm. Speedups for ray tracing were found to be in the range of 2.1–10.1, relative to the multithreaded PLATO algorithm running four threads. For dose calculations the speedup measured was in the range of 1.5–6.2. For the speedup of both the ray tracing and the dose calculation, a strong dependency on the tested geometry was found. This dependency is related to the fraction of air within the patient's bounding box resulting in idle threads.Conclusions:With the use of a GPU, ray tracing for dose calculations can be performed accurately in considerably less time. Ray tracing was accelerated, on average, with a factor of 6 for the evaluated cases. Dose calculation for a single beam can typically be carried out in for clinically realistic datasets. These findings can be used in conventional planning to enable (nearly) real‐time dose calculations. Also the importance for treatment optimization techniques is evident.
Effect of prolonged stimulation on cerebral hemodynamic: A time‐resolved fNIRS study
Authors: Butti Michele , Contini Davide , Molteni Erika , Caffini Matteo , Spinelli Lorenzo , Baselli Giuseppe , Bianchi Anna Maria , Cerutti Sergio , Cubeddu Rinaldo , Torricelli Alessandro 
Published: August 2009

Purpose:Sustained attention is one of the most important cognitive abilities for the management of everyday life, but it is often studied only at the behavioral level, while functional correlates are scarcely investigated. In this article, the authors address the topic of characterizing the dynamics of cerebral metabolism in the prefrontal cortex during a task of prolonged attention.Method:By means of multichannel time‐resolved functional near‐infrared spectroscopy and generalized linear model based data processing, the authors measured the hemodynamic response of the prefrontal cortex from 19 healthy subjects to a shortened version of a sustained attention task (Conners’ Continuous Performance Test), lasting for.Results:The task elicited significant brain activation, which did not remain constant for the entire task, but showed a drop not correlated with performance decay after the beginning of the task. Furthermore, oxygenated hemoglobin showed an increasing trend also during the first phase of the recovery, just after the end of the task.Conclusion:The results indicate a nontrivial dynamics of neural activation, habituation processes, and hemodynamic/metabolic coupling. These results encourage further studies about continuous stimulation of cognitive functions on both healthy and pathological subjects.
‐band EPR imaging as a tool for gradient dose reconstruction in irradiated bones
Authors: Levêque Philippe , Godechal Quentin , Bol Anne , Trompier François , Gallez Bernard 
Published: August 2009

Purpose:Various tools are currently available for dose reconstruction in individuals after accidental exposure to ionizing radiation. Among the available biological analyses, Monte Carlo simulations, and biophysical methods, such as electron paramagnetic resonance (EPR), the latter has proved its usefulness for retrospective dosimetry. Although EPR spectroscopy is probably the most sensitive technique, it does not provide spatial dosimetric data. This information is, however, highly desirable when steep dose gradient irradiations are involved. The purpose of this work was to explore the possibilities of EPR imaging (EPRI) for spatial dose reconstruction in irradiated biological material.Methods:‐band EPRI was used to reconstruct ex vivo the relative dose distribution in human bone samples and hydroxyapatite phantoms after irradiation with brachytherapy seeds or x rays. Three situations were investigated: Homogeneous, stepwise gradient, and continuous gradient irradiation.Results:EPRI gave a faithful relative spin density distribution in bone samples and in hydroxyapatite phantoms. Measured dose ratios were in close agreement with the actual delivered dose ratios. EPRI was able to distinguish the dose gradients induced by two different sources ( and ). However, the measured spatial resolution of the system was 1.9 mm and this appeared to be a limiting factor. The method could be improved by using new signal postprocessing strategies.Conclusions:This study demonstrates that EPRI can be used to assess the regional relative dose distribution in irradiated bone samples. The method is currently applicable toex vivo measurements of small size samples with low variation in tissue density but is likely to be adapted for in vivo application using ‐band EPRI.
Mushroom tyrosinase-modified carbon paste electrode as an amperometric biosensor for phenols
Authors: Skládal Petr 
Published: August 2009

A biosensor for a variety of substances could be readily prepared by the adsorption of partially purified mushroom tyrosinase at a carbon paste electrode, producing an enzyme layer which was protected with a dialysis membrane. The electrode poised at – 100mV (vs an Ag/AgCl reference electrode) functions on the basis of a reversible electrochemical reduction of the o-quinones formed from phenols in the tyrosinase reaction. The response times were 40 s for o-diphenols and 2 min for monophenols; the reproducibility for 10 consecutive assays of 3 μmol l-1 phenol solution was better than 4%. The detection limit was 10 nmol l-1 (catechol as substrate) and the steady state responses were linear up to a concentration of 200 μmol l-1. The optimum pH values were 6.0 for phenol and 6.5 for catechol. The shapes of the pH-response curves indicated the presence of at least two tyrosinase isoenzymes with different pH optima.
"I'm Not an Activist!": Animal Rights vs. Animal Welfare in the Purebred Dog Rescue Movement
Authors: Greenebaum Jessica 
Published: August 2009

AbstractPurebred dog rescuers are doing their part to reduce the problems of homeless pets and pet overpopulation. The volunteers studied are doing the daily and invisible work of saving dogs. Because of their perception of the animal rights movement, however, they do not consider themselves part of the animal welfare or animal rights movement, nor do they care to be. Dog rescue organizations agree with academics and activist organizations on the cause of the problem of homeless pets and pet overpopulation, but they differ on the theoretical, political, and ideological solutions to the problem. This paper focuses on the disagreements between rescue workers, activists, and academics and asks whether there is a place for rescue workers within the larger animal protection movement.