bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impact of Plants Introduced by People During a Time of Rapid Environmental Change
Authors: Holland Peter , Woodland Dennis W. , Hetherington Jillian 
Published: June 2010

AbstractRelatively few of the many plant species introduced by people have become naturalized, and only a small fraction of them have had a major impact on native species and ecosystems. The risks they pose are driven by environmental disturbance, but whether or not introduced plants cause extinction of native species remains uncertain, nor can we state with certainty which will become established in new areas and persist there without direct or indirect human assistance. It may take decades for some introduced plants to pose a threat to native species whereas others could do so in a few years, but several researchers have argued that until recently the time dimension has received comparatively little attention. The literature shows that the conservational and ecological problems caused by introduced plants do not simply stem from competition with native plants for space, light, nutrients and water. Rather, they involve spatial and temporal combinations of genetics and growth behaviour as well as differential responses to ecological opportunities, how newcomers fit into the biological and environmental structures of the host ecosystem, and the involvements of people, plants and animals. This article argues for long‐term, integrated programmes of observation and experimentation in the field and laboratory into the risks that introduced plants pose for native species and ecosystems.
Los efectos de la crisis de 2007‐2009 en los fondos de pensiones privados y de la seguridad social: ¿una amenaza para su solidez financiera?
Authors: Pino Ariel , Yermo Juan 
Published: June 2010

ResumenLa reciente crisis financiera ha tenido una repercusión sin precedentes en los fondos de pensiones y de la seguridad social. Estos últimos han registrado importantes pérdidas no realizadas en sus inversiones y se han impugnado sus mecanismos de administración, lo que ha puesto en peligro su solidez financiera y cuestionado su capacidad de proporcionar prestaciones adecuadas. El año 2009 finalizó con la recuperación de los mercados financieros, así como con la reasignación de las carteras y la reformulación de los enfoques tradicionales de gestión de riesgos. Los gobiernos han reaccionado frente a la crisis y han aplicado planes de recuperación que podrían suponer una amenaza para la situación fiscal a medio plazo. Es posible que la presión fiscal posterior a la crisis genere una situación de compromiso entre el restablecimiento de la solidez fiscal y la reducción del gasto social. En el presente artículo se analizan los efectos de la crisis en los fondos de pensiones y de la seguridad social y se abordan las cuestiones antes mencionadas.
El impacto de la crisis financiera global en la protección social de los países en desarrollo
Authors: McCord Anna 
Published: June 2010

ResumenLa crisis financiera global ha tenido un efecto devastador en los niveles de pobreza de los países en desarrollo, y la respuesta de la protección social hasta la fecha, en forma de asistencia social, ha sido limitada y se ha visto constreñida por la debilidad de los sistemas y la baja cobertura de las prestaciones preexistentes. Debido a la reducción de los ingresos, a los países en desarrollo les resulta muy difícil respetar sus compromisos políticos en materia de protección social anteriores a la crisis, apenas existiendo potencial, en este contexto, para extender la cobertura y asistir a quienes se han empobrecido aún más y a los «nuevos pobres». A pesar de que muchos países en desarrollo han adoptado soluciones de expansionismo fiscal, las respuestas políticas a la crisis se han centrado en proteger y estimular el crecimiento. Las soluciones adoptadas no han dado prioridad a la provisión de protección social para ayudar directamente a los pobres. En aquellos casos en los que se han producido intervenciones de protección social, en general, se ha tratado de intervenciones exclusivamente ad hoc y, frecuentemente, han sido intervenciones regresivas — como los subsidios generalizados para alimentos o carburantes — en vez de tratarse de intervenciones más sistémicas y favorables a los pobres. No obstante, existe un cierto margen para el optimismo, puesto que la crisis ha estimulado una serie de iniciativas encaminadas a promover la coordinación de donantes y la compatibilidad de la programación, lo cual puede traducirse en una mejora de la eficacia y el impacto de los futuros programas de protección social.
La seguridad social en tiempos de crisis
Authors: Bonnet Florence , Ehmke Ellen , Hagemejer Krzysztof 
Published: June 2010

ResumenPara contrarrestar los efectos sociales negativos de la crisis actual, los Estados deben adoptar medidas para proporcionar ayuda a los ingresos y nuevas oportunidades de empleo a los trabajadores afectados y sus familias. En este artículo se examinan las respuestas a la crisis aportadas por algunos países a través de programas de desempleo, que es la rama de la seguridad social más afectada por la desaceleración económica. Se abordan asimismo las situaciones de compromiso a las que los regímenes de seguridad social en su conjunto deben hacer frente durante las crisis económicas, cuando disminuyen los ingresos provenientes de cotizaciones e impuestos destinados a financiar los programas y se incrementa el gasto en prestaciones. También se presta especial atención a las preocupaciones que suscitan las políticas en materia de pensiones. Por último, se aborda la iniciativa propuesta por las Naciones Unidas en favor de un «nivel mínimo de protección social» en el plano mundial destinado a facilitar, al menos, protección social básica a la gran mayoría de la población mundial que carece actualmente de cobertura social y sigue siendo vulnerable a los riesgos económicos y sociales.
Crisis económica y protección social en la Unión Europea: más allá de lo evidente
Authors: Euzéby Alain 
Published: June 2010

ResumenLa crisis económica tiene al menos la virtud de poner de manifiesto que la protección social es a la vez un amortiguador social y un estabilizador económico que limita la gravedad de la recesión. De hecho, los países de la Unión Europea, incluso la misma Unión, en el marco de su plan de recuperación económica, utilizan las prestaciones sociales para ayudar a las personas afectadas por la crisis, estimular el consumo de las familias y, de este modo, respaldar la actividad de las empresas y favorecer el empleo. Por otra parte, la crisis también puede ofrecer a la Unión Europea una oportunidad para reforzar sus sistemas de protección social, inspirándose en los grandes principios del derecho social internacional, afirmando la legitimidad de niveles de protección social altos, favoreciendo la convergencia hacia los sistemas de protección social de mayor cobertura entre los Estados miembros, e incrementando su presupuesto.
Treatment plans optimization for contrast‐enhanced synchrotron stereotactic radiotherapy
Authors: Edouard M. , Broggio D. , Prezado Y. , Estève F. , Elleaume H. , Adam J. F. 
Published: June 2010

PurposeSynchrotron stereotactic radiotherapy (SSRT) is a treatment that involves the targeting of high‐ elements into tumors followed by stereotactic irradiation with monochromatic x‐rays from a synchrotron source, tuned at an optimal energy. The irradiation geometry, as well as the secondary particles generated at a higher yield by the medium energy x‐rays on the high‐ atoms (characteristic x‐rays, photoelectrons, and Auger electrons), produces a localized dose enhancement in the tumor. Iodine‐enhanced SSRT with systemic injections of iodinated contrast agents has been successfully developed in the past six years in the team, and is currently being transferred to clinical trials. The purpose of this work is to study the impact on the SSRT treatment of the contrast agent type, the beam quality, the irradiation geometry, and the beam weighting for defining an optimized SSRT treatment plan.MethodsTheoretical dosimetry was performed using theMCNPX particle transport code. The simulated geometry was an idealized phantom representing a human head. A virtual target was positioned in the central part of the phantom or off‐centered by 4 cm. The authors investigated the dosimetric characteristics of SSRT for various contrast agents: Iodine, gadolinium, and gold; and for different beam qualities: Monochromatic x‐ray beams from a synchrotron source (30–120 keV), polychromatic x‐ray beams from an x‐ray tube (80, 120, and 180 kVp), and a 6 MV x‐ray beam from a linear accelerator. Three irradiation geometries were studied: One arc or three noncoplanar arcs dynamic arc therapy, and an irradiation with a finite number of beams. The resulting dose enhancements, beam profiles, and histograms dose volumes were compared for iodine‐enhanced SSRT. An attempt to optimize the irradiation scheme by weighing the finite x‐ray beams was performed. Finally, the optimization was studied on patient specific 3D CT data after contrast agent infusion.ResultsIt was demonstrated in this study that an 80 keV beam energy was a good compromise for treating human brain tumors with iodine‐enhanced SSRT, resulting in a still high dose enhancement factor (about 2) and a superior bone sparing in comparison with lower energy x‐rays. This beam could easily be produced at the European Synchrotron Radiation Facility medical beamline. Moreover, there was a significant diminution of dose delivered to the bone when using monochromatic x‐rays rather than polychromatic x‐rays from a conventional tube. The data showed that iodine SSRT exhibits a superior sparing of brain healthy tissue in comparison to high energy treatment. The beam weighting optimization significantly improved the treatment plans for off‐centered tumors, when compared to nonweighted irradiations.ConclusionsThis study demonstrated the feasibility of realistic clinical plans for low energy monochromatic x‐rays contrast‐enhanced radiotherapy, suitable for the first clinical trials on brain metastasis with a homogeneous iodine uptake.
Characterization of a unit at a secondary standard dosimetry laboratory: Monte Carlo simulations compared to measurements and results from the literature
Authors: Tedgren Åsa Carlsson , de Luelmo Sandro , Grindborg Jan‐Erik 
Published: June 2010

PurposeTo compare a Monte Carlo (MC) characterization of a unit at the Swedish Secondary Standard Dosimetry Laboratory (SSDL) with the results of both measurements and literature with the aims of (1) resolving a change in the ratio of air‐kerma free in air and absorbed dose to water in a water phantom noted experimentally after a source exchange in the laboratory and (2) reviewing results from the literature on similar MC simulations. Although their use in radiotherapy is decreasing, the characteristics of beams are of interest since beams are utilized in calibrating ionization chambers for the absolute dosimetry of radiotherapy beams and as reference radiation quality in evaluating the energy dependence of radiation detectors and in studies on radiobiological effectiveness.MethodsThe BEAMnrc MC code was used with a detailed geometrical model of the treatment head and two models of the source representing the sources used before and after source exchange, respectively. The active diameters of the sources were 1.5 cm in pellet form and 2.0 cm in sintered form. Measurements were performed on the actual unit at the Swedish SSDL.ResultsAgreement was obtained between the MC and the measured results within the estimated uncertainties for beam profiles, water depth‐dose curve, relative air‐kerma output factors, and for the ratios of before and after source exchange. The on‐axis energy distribution of the photon fluence free in air for the unit loaded with its present (1.5 cm in diameter) source agreed closely with the results from the literature in which a source of the same make and active diameter, inside a different treatment head, was simulated. The spectrum for the larger (2.0 cm in diameter) source was in close agreement with another published spectrum, also modeling a source with an active diameter of 2.0 cm inside a different treatment head.ConclusionsThe reduction in the value of following source exchange was explained by the spectral differences between the two sources that were larger in the free in‐air geometry used for calibrations than at depth in the water phantom used for calibrations. Literature review revealed differences between published in‐air spectra derived for sources of different active diameters, and investigators in need of an accurately determined in‐air spectrum should be aware of differences due to source active diameter.
A field size specific backscatter correction algorithm for accurate EPID dosimetry
Authors: Berry Sean L. , Polvorosa Cynthia S. , Wuu Cheng‐Shie 
Published: June 2010

PurposePortal dose images acquired with an amorphous silicon electronic portal imaging device (EPID) suffer from artifacts related to backscattered radiation. The backscatter signal varies as a function of field size (FS) and location on the EPID. Most current portal dosimetry algorithms fail to account for the FS dependence. The ramifications of this omission are investigated and solutions for correcting the measured dose images for FS specific backscatter are proposed.MethodsA series of open field dose images were obtained for field sizes ranging from to . Each image was analyzed to determine the amount of backscatter present. Two methods to account for the relationship between FS and backscatter are offered. These include the use of discrete FS specific correction matrices and the use of a single generalized equation. The efficacy of each approach was tested on the clinical dosimetric images for ten patients, 49 treatment fields. The fields were evaluated to determine whether there was an improvement in the dosimetric result over the commercial vendor's current algorithm.ResultsIt was found that backscatter manifests itself as an asymmetry in the measured signal primarily in the inplane direction. The maximum error is approximately 3.6% for and field sizes. The asymmetry decreased with increasing FS to approximately 0.6% for fields larger than . The dosimetric comparison between the measured and predicted dose images was significantly improved when a FS specific backscatter correction was applied. The average percentage of points passing a 2%, 2 mm gamma criteria increased from 90.6% to between 96.7% and 97.2% after the proposed methods were employed.ConclusionsThe error observed in a measured portal dose image depends on how much its FS differs from the calibration conditions. The proposed methods for correcting for FS specific backscatter effectively improved the ability of the EPID to perform dosimetric measurements. Correcting for FS specific backscatter is important for accurate EPID dosimetry and can be carried out using the methods presented within this investigation.
A method for MRI guidance of intercostal high intensity focused ultrasound ablation in the liver
Authors: Quesson Bruno , Merle Mathilde , Köhler Max O. , Mougenot Charles , Roujol Sebastien , de Senneville Baudouin Denis , Moonen Chrit T. 
Published: June 2010

PurposeHigh intensity focused ultrasound (HIFU) is a promising method for the noninvasive treatment of liver tumors. However, the presence of ribs in the HIFU beam path remains problematic since it may lead to adverse effects (skin burns) by absorption and reflection of the incident beam at or near the bone surface. This article presents a method based on magnetic resonance (MR) imaging for identification of the ribs in the HIFU beam, and for selection of the transducer elements to deactivate.MethodsThe ribs are visualized on anatomical images acquired prior to heating and manually segmented. The resulting regions of interest surrounding the ribs are projected onto the transducer surface by ray tracing from the focal point. The transducer elements in the “shadow” of the ribs are then deactivated. The method was validatedex vivo and in vivo in pig liver during breathing under multislice real‐time MR thermometry, using the proton resonance frequency shift method.ResultsEx vivo and in vivo temperature data showed that the temperature increase near the ribs was substantial when HIFU sonications were performed with all elements active, whereas the temperature was reduced with deactivation of the transducer elements located in front of the ribs. The temperature at the focal point was similar with and without deactivation of the transducer elements, indicative of no loss of heat efficiency with the proposed technique.ConclusionsThis method is simple, rapid, and reliable, and enables intercostal HIFU ablation while sparing ribs and their surrounding tissues.
Uncertainties in IMRT dosimetry
Authors: Li Jin Sheng , Lin Teh , Chen Lili , Price Robert A. , Ma Chang‐Ming 
Published: June 2010

PurposeThe purpose of this study is to investigate some characteristics of the beam delivery system and their effects on the dose distribution of intensity‐modulated radiation therapy (IMRT) and the results of patient‐specific IMRT quality assurance (QA). These characteristics include the accelerator source distribution and multileaf collimator (MLC) geometry.MethodsMonte Carlo dose calculations based on intensity maps that were built from the actual deliverable IMRT leaf sequences with and without considering the characteristics of the beam delivery system were performed in this study using in‐house Monte Carlo software. The effect of the resolution of the intensity maps on the dose distribution was investigated first. The mean dose of the treatment target and the voxel doses in the high dose region of seven IMRT plans generated by different treatment planning systems for Varian 21EX and Siemens Primus linear accelerators were used for comparison and evaluation.ResultsThe results show that a or smaller pixel size is needed for the intensity maps for accurate IMRT dose calculation. The extrafocal source, MLC leaf thickness, leakage, tongue‐and‐groove structure, and the effective leaf offset can affect the mean dose by up to 1.5%, 4.5%, 5.6%, 5.3%, and 7.8%, respectively, when these factors are considered separately. They also cause significant uncertainties to the voxel dose with standard deviations up to 2.5%, 0.7%, 2.1%, 1.3%, and 5%, respectively. The overall effect on the mean dose is up to 8% and the standard deviation of the voxel dose uncertainty is up to 6.4% when all the effects are included. The maximum standard deviation is reduced to 4.6% if the voxel size of the dose calculation matrix is increased from 0.04 to to make it comparable with the sensitive volume of the ionization chamber used for IMRT QA measurements.ConclusionsIt can be concluded that the characteristics of the beam delivery system are the major contributors to the uncertainty of measurement‐based IMRT QA because most of them are not fully considered in the currently available treatment planning systems.
A quality assurance tool for high‐dose‐rate brachytherapy
Authors: Rickey Daniel W. , Sasaki David , Bews Jeff 
Published: June 2010

Purpose: The purpose of this work was to develop a quality assurance (QA) tool for high‐dose‐rate (HDR) brachytherapy that would quickly and easily verify both source positioning (dwell positions) and durations (dwell times).Methods: The authors constructed a QA tool that combined radiochromic film to verify position with four photodiode detectors to verify dwell times. To characterize the temporal accuracy of the tool, a function generator powered four red light‐emitting diodes that were optically coupled to the four photodiode detectors. The QA tool was used to verify the dwell positions and times of a commercial brachytherapy afterloader. Measurements of dwell time were independently verified by a one‐dimensional optical camera that acquired 1000 lines/s.Results: The temporal accuracy of the QA tool was found to be about 1 ms. For visual assessment, the source position could be located within about 0.5 mm. Evaluating the accuracy and precision of an HDR brachytherapy afterloader, the authors found that the bias in dwell time can exceed 60 ms and the dwell time associated with the first dwell position had an unexpectedly large standard deviation of 30 ms. They found that the source locations were much easier to locate on the film if a plastic catheter was used instead of a metal treatment tube. Scanning the films enabled the dwell positions to be determined within about 0.2 mm.Conclusions: For pretreatment QA, the authors found that this tool allowed verification of dwell positions and dwell times in about 6 min.
Real‐time volumetric image reconstruction and 3D tumor localization based on a single x‐ray projection image for lung cancer radiotherapy
Authors: Li Ruijiang , Jia Xun , Lewis John H. , Gu Xuejun , Folkerts Michael , Men Chunhua , Jiang Steve B. 
Published: June 2010

PurposeTo develop an algorithm for real‐time volumetric image reconstruction and 3D tumor localization based on a single x‐ray projection image for lung cancer radiotherapy.MethodsGiven a set of volumetric images of a patient at breathing phases as the training data, deformable image registration was performed between a reference phase and the other phases, resulting in deformation vector fields (DVFs). These DVFs can be represented efficiently by a few eigenvectors and coefficients obtained from principal component analysis (PCA). By varying the PCA coefficients, new DVFs can be generated, which, when applied on the reference image, lead to new volumetric images. A volumetric image can then be reconstructed from a single projection image by optimizing the PCA coefficients such that its computed projection matches the measured one. The 3D location of the tumor can be derived by applying the inverted DVF on its position in the reference image. The algorithm was implemented on graphics processing units (GPUs) to achieve real‐time efficiency. The training data were generated using a realistic and dynamic mathematical phantom with ten breathing phases. The testing data were 360 cone beam projections corresponding to one gantry rotation, simulated using the same phantom with a 50% increase in breathing amplitude.ResultsThe average relative image intensity error of the reconstructed volumetric images is . The average 3D tumor localization error is . On an NVIDIA Tesla C1060 GPU card, the average computation time for reconstructing a volumetric image from each projection is 0.24 s (range: 0.17 and 0.35 s).ConclusionsThe authors have shown the feasibility of reconstructing volumetric images and localizing tumor positions in 3D in near real‐time from a single x‐ray image.