Impact of use of optical surface imaging on initial patient setup for stereotactic body radiotherapy treatments

Purpose To evaluate the effectiveness of surface image guidance (SG) for pre‐imaging setup of stereotactic body radiotherapy (SBRT) patients, and to investigate the impact of SG reference surface selection on this process. Methods and materials 284 SBRT fractions (SG‐SBRT = 113, non‐SG‐SBRT = 171) were retrospectively evaluated. Differences between initial (pre‐imaging) and treatment couch positions were extracted from the record‐and‐verify system and compared for the two groups. Rotational setup discrepancies were also computed. The utility of orthogonal kVs in reducing CBCT shifts in the SG‐SBRT/non‐SG‐SBRT groups was also calculated. Additionally, the number of CBCTs acquired for setup was recorded and the average for each cohort was compared. These data served to evaluate the effectiveness of surface imaging in pre‐imaging patient positioning and its potential impact on the necessity of including orthogonal kVs for setup. Since reference surface selection can affect SG setup, daily surface reproducibility was estimated by comparing camera‐acquired surface references (VRT surface) at each fraction to the external surface of the planning CT (DICOM surface) and to the VRT surface from the previous fraction. Results The reduction in all initial‐to‐treatment translation/rotation differences when using SG‐SBRT was statistically significant (Rank‐Sum test, α = 0.05). Orthogonal kV imaging kept CBCT shifts below reimaging thresholds in 19%/51% of fractions for SG‐SBRT/non‐SG‐SBRT cohorts. Differences in average number of CBCTs acquired were not statistically significant. The reference surface study found no statistically significant differences between the use of DICOM or VRT surfaces. Conclusions SG‐SBRT improved pre‐imaging treatment setup compared to in‐room laser localization alone. It decreased the necessity of orthogonal kV imaging prior to CBCT but did not affect the average number of CBCTs acquired for setup. The selection of reference surface did not have a significant impact on initial patient positioning

Primitive model electrolytes. A comparison of the HNC approximation for the activity coefficient with Monte Carlo data

Accuracy of the mean activity coefficient expression (Hansen-Vieillefosse-Belloni equation), valid within the hypernetted chain (HNC) approximation, was tested in a wide concentration range against new Monte Carlo (MC) data for +1:-1 and +2:-2 primitive model electrolytes. The expression has an advantage that the excess chemical potential can be obtained directly, without invoking the time consuming Gibbs-Duhem calculation. We found the HNC results for the mean activity coefficient to be in good agreement with the machine calculations performed for the same model. In addition, the thermodynamic consistency of the HNC approximation was tested. The mean activity coefficients, calculated via the Gibbs-Duhem equation, seem to follow the MC data slightly better than the Hansen-Vieillefosse-Belloni expression. For completeness of the calculation, the HNC excess internal energies and osmotic coefficients are also presented. These results are compared with the calculations based on other theories commonly used to describe electrolyte solutions, such as the mean spherical approximation, Pitzer's extension of the Debye-H\"uckel theory, and the Debye-H\"uckel limiting law.Comment: 15 pages, 6 figure

Uniqueness of static decompositions

We classify static manifolds which admit more than one static decomposition whenever a condition on the curvature is fullfilled. For this, we take a standard static vector field and analyze its associated one parameter family of projections onto the base. We show that the base itself is a static manifold and the warping function satisfies severe restrictions, leading us to our classification results. Moreover, we show that certain condition on the lightlike sectional curvature ensures the uniqueness of static decomposition for Lorentzian manifolds.Comment: 14 page

La construcción social de la pobreza. Un análisis desde las categorías de Pierre Bordieu

La pobreza puede construirse, a partir de las categorías analíticas de Pierre Bourdieu, como un fenómeno clave de la reproducción de la sociedad y de sus mecanismos de dominación. Para ello, y desde esa teoría, primero, se plantean preguntas y desafíos a otras maneras de abordar el fenómeno, desde la noción misma de «pobreza», pasando por la llamada «perspectiva de la marginalidad», y aquellas otras, ligadas a la noción de «estrategia». Luego se presenta una conceptualización del espacio social y de las estrategias de reproducción que ponen en marccha las clases, intentando responder a las preguntas sugeridas. Se consideran los factores explicativos de dichas estrategias ligadas al fenómeno de la pobreza: el volumen y la estructura del capital, los instrumentos de reproducción, el estado de relación de fuerzas entre las clases y los habitus incorporados.Poverty can be treated, in accordance with the analytic categories of Pierre Bourdieu, as a key phenomenon of the reproduction of society and its mechanisms of domination. With respect to this theoretical approach, firstly, questions and challenges are made which aim at alternative ways of boarding the phenomenon, such as the proper notion of «poverty», or the so called «perspective of marginalization» and all those others bound to the notion of «strategy». Afterwards, a conceptualization of the social space and the strategies of reproduction, developed by the social classes, is proposed, in order to answer the questions that were suggested. The explanative elements of those strategies, related with the phenomenon of poverty, are discussed, such as the volume and structure of the capital, the instruments of reproduction, the state of the relation of forces between the classes, and the incorporated habitus

Conglomerados asiáticos y regionalismo en el Cono Sur americano

La globalización está redefiniendo los espacios, procesos y actores del desarrollo latinoamericano. El propósito de este artículo es analizar los nuevos procesos de integración y los emergentes sistemas de negocios en el Cono Sur latinoamericano a la luz de los vínculos con las economías del Este asiático. En particular, estudia los niveles y formas de interacción de los agentes económicos asiáticos, principalmente los grandes grupos empresariales japoneses y coreanos en los dos espacios económicos latinoamericanos: México, Centroaméricay el Caribe, por una parte, y el Cono Sur latinoamericano por la otra

«Con Marx y contra Marx»: el materialismo en Pierre Bourdieu

Bourdieu ha dicho explícitamente a lo largo de su trabajo que su construcción teórica se ha inspirado en los tres pilares de la sociología: Marx, Durkheim y Max Weber. Por ello, al hacer hincapié en la presencia del materialismo en Pierre Bourdieu, es necesario simultáneamente hacer referencia a los otros dos sociólogos mencionados. Entre los acercamientos a Marx, se señala el rechazo a la teoría pura, la construcción del hecho científico, la insistencia en la explicación de los fenómenos sociales por sus causas sociales e históricas, el principio de la no-conciencia y la ilusión de la transparencia, la concepción relacional de lo social y la concepción agonística de la acción social. En la dialéctica acercamientos-rupturas con Marx, se trabaja especialmente la «economía de las prácticas» y la teoría de las clases en sus dos dimensiones: su construcción y su papel en la explicación de las prácticas sociales.Bourdieu has explicitly said along hiswork that his theoretical construction has been inspired in the pillars of Sociology: Marx, Durkheim and Max Weber. For this reason, when emphasizing the presence of materialism in Pierre Bourdieu, it is necessary at the same time to make reference to the other sociologists above mentioned. Referring ti Marx’ approaches, the reject to pure theory is pointed out as well as the construction of the scientific fact, the insistence on the explanation of social phenomena by its social and historical causes, the principle of the «non-conscience», and the illusion of transparency, the relational conception of the social events and the agonistic conception of the social action. In the dialectic approaches-ruptures with Marx, the «economy of practices» and the theory of classes are specially treated and its two dimensions: its construction and its role explaining social practices