Assesing multileaf collimator effect on the build-up region using Monte Carlo method

Previous Monte Carlo studies have investigated the multileaf collimator (MLC) contribution to the build-up region for fields in which the MLC leaves were fully blocking the openings defined by the collimation jaws. In the present work, we investigate the same effect but for symmetric and asymmetric MLC defined field sizes (2×2, 4×4, 10×10 and 3×7 cm2). A Varian 2100C/D accelerator with 120-leaf MLC is accurately modeled fora6MVphoton beam using the BEAMnrc/EGSnrc code. Our results indicate that particles scattered from accelerator head and MLC are responsible for the increase of about 7% on the surface dose when comparing 2×2 and 10×10 cm2 fields. We found that the MLC contribution to the total build-up dose is about 2% for the 2×2 cm2 field and less than 1% for the largest fields

The use of non-standard CT conversion ramps for Monte Carlo verification of 6 MV prostate IMRT plans

Monte Carlo (MC) dose calculation algorithms have been widely used to verify the accuracy of intensity-modulated radiotherapy (IMRT) dose distributions computed by conventional algorithms due to the ability to precisely account for the effects of tissue inhomogeneities and multileaf collimator characteristics. Both algorithms present, however, a particular difference in terms of dose calculation and report. Whereas dose from conventional methods is traditionally computed and reported as the water-equivalent dose (Dw), MC dose algorithms calculate and report dose to medium (Dm). In order to compare consistently both methods, the conversion of MC Dm into Dw is therefore necessary. This study aims to assess the effect of applying the conversion of MC-based Dm distributions to Dw for prostate IMRT plans generated for 6 MV photon beams. MC phantoms were created from the patient CT images using three different ramps to convert CT numbers into material and mass density: a conventional four material ramp (CTCREATE) and two simplified CT conversion ramps: (1) air and water with variable densities and (2) air and water with unit density. MC simulations were performed using the BEAMnrc code for the treatment head simulation and the DOSXYZnrc code for the patient dose calculation. The conversion of Dm to Dw by scaling with the stopping power ratios of water to medium was also performed in a post-MC calculation process. The comparison of MC dose distributions calculated in conventional and simplified (water with variable densities) phantoms showed that the effect of material composition on dose-volume histograms (DVH) was less than 1% for soft tissue and about 2.5% near and inside bone structures. The effect of material density on DVH was less than 1% for all tissues through the comparison of MC distributions performed in the two simplified phantoms considering water. Additionally, MC dose distributions were compared with the predictions from an Eclipse treatment planning system (TPS), which employed a pencil beam convolution (PBC) algorithm with Modified Batho Power Law heterogeneity correction. Eclipse PBC and MC calculations (conventional and simplified phantoms) agreed well (<1%) for soft tissues. For femoral heads, differences up to 3% were observed between the DVH for Eclipse PBC and MC calculated in conventional phantoms. The use of the CT conversion ramp of water with variable densities for MC simulations showed no dose discrepancies (0.5%) with the PBC algorithm. Moreover, converting Dm to Dw using mass stopping power ratios resulted in a significant shift (up to 6%) in the DVH for the femoral heads compared to the Eclipse PBC one. Our results show that, for prostate IMRT plans delivered with 6 MV photon beams, no conversion of MC dose from medium to water using stopping power ratio is needed. In contrast, MC dose calculations using water with variable density may be a simple way to solve the problem found using the dose conversion method based on the stopping power ratio

Dolomite crystal morphologies in dolocretes and lacustrine deposits from the Madrid and Almazán basins

Comunicación presentada en el IX Congreso Geológico de España, Huelva, 12-14 septiembre 2016.[ES] Este trabajo describe morfologías de cristales de dolomita, observados tanto en microscopio petrográfico como electrónico, de dolocretas y de depósitos carbonático-evaporíticos de ambientes lacustres someros, tanto del Paleógeno de la Cuenca de Almazán como del Mioceno de la Cuenca de Madrid. Se han identificado 6 morfotipos: 1) Tubos de dolomita; 2) Cilindros de dolomita vacuolar; 3) Romboedros de dolomita; 4) Cristales de dolomita esferoidal; 5) Cristales de dolomita con forma de capullo; y 6) Dolomita en mancuerna. Las morfologías dominantes en dolocretas son los romboedros, los esferoides, y las mancuernas. Por otro lado, en los depósitos lacustres la variedad de morfologías es mucho mayor, siendo las más comunes: los tubos, los cilindros de dolomita vacuolar, los esferoides y los cristales de dolomita con forma de capullo. La morfología de los cristales de dolomita puede ser un indicador de procesos bióticos o abióticos en su precipitación, aunque han de tenerse en cuenta otros indicadores para comprender la influencia de dichos procesos.[EN] This paper describes the dolomite crystal morphologies, observed under petrographic microscope and SEM, from dolocretes and carbonate-evaporitic lacustrine deposits. Samples analysed come from the Paleogene of the Almazán basin and the Miocene of the Madrid basin. Six morphotypes have been identified: 1) Dolomite tubes; 2) Vacuolar dolomite cylinders; 3) Rhombohedral dolomite crystals; 4) Spheroidal dolomite crystals; 5) Cocoon-shaped dolomite crystals; and 6) Dolomite dumbbells. Dominant morphotypes in dolocretes are: rhomboids; spheroids, and dumbbells. In lacustrine deposits the variety is higher and includes tubes, vacuolar dolomite cylinders, spheroids and cocoon-shaped dolomite crystals. Dolomite crystal morphology can be indicative of biotic or abiotic processes in dolomite precipitation, but other evidences must be taken into account to understand the influence of the mentioned processes.Este trabajo ha sido financiado por los proyectos de investigación CGL-2011-27826-CO2-02 y CGL2014- 54818-P del Ministerio de Economía y Competitividad.Peer reviewe

Performance of a direct steam generation solar thermal power plant for electricity production as a function of the solar multiple

This paper describes the influence of the solar multiple on the annual performance of parabolic trough solar thermal power plants with direct steam generation (DSG). The reference system selected is a 50 M We DSG power plant, with thermal storage and auxiliary natural gas-fired boiler. It is considered that both systems are necessary for an optimum coupling to the electricity grid. Although thermal storage is an opening issue for DSG technology, it gives an additional degree of freedom for plant performance optimization. Fossil hybridization is also a key element if a reliable electricity production must be guaranteed for a defined time span. Once the yearly parameters of the solar power plant are calculated, the economic analysis is performed, assessing the effect of the solar multiple in the levelized cost of electricity, as well as in the annual natural gas consumption

Geolodía: a yearly successful organization of 54 geological fieldtrips in a weekend oriented to nongeologists Geolodía: Why and how to organize 54 geological fieldtrips in a weekend oriented to nongeologists?

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

(Z)-4-[3-(2,5-Dioxoimidazolidin-4-ylidenemeth­yl)-1H-indol-1-ylmeth­yl]benzonitrile

In the title compound, C20H14N4O2, mol­ecules are linked into chains by N—H⋯O hydrogen bonds, but the cyano group does not participate in the supra­molecular aggregation. The crystal structure of the compound indicates the presence of a double bond with Z geometry, connecting the imidazolidine and indole units. The dihedral angle between the imidazole and benzene ring planes is 62.45 (4)°

La fotografía animada: La vivienda extranjera vista por el NO-DO

Frente a las revistas profesionales dedicadas a la arquitectura, el NO-DO (Noticiarios y Documentales Cinematográficos) es otro vehículo de difusión de la misma destinado a la población en general durante casi 40 años en España (1943-1981). A través de estos noticiarios de estado, que se proyectan obligatoriamente en los cines de todo el territorio nacional, la arquitectura aparece mezclada con un sinfín de noticias variopintas. Dentro de la arquitectura, la vivienda tiene un tratamiento preferente, tanto la que se construye en el país, con el incesante surgimiento de nuevos pueblos y barrios urbanos, como la vivienda extranjera, que el noticiario considera emblema de lo moderno. La imagen de la vivienda extranjera que transmite el noticiario NO-DO es heterogénea y responde básicamente a cuatro tipos de noticias recurrentes en las pantallas: Las configuraciones geométricas más curiosas o extrañas para la población en general, los nuevos materiales, las nuevas técnicas constructivas e instalaciones, las construcciones residenciales en ubicaciones o situaciones especiales y las exposiciones que muestran los avances de la vivienda.Along with professional specialized magazines, NO-DO (Newsreels and Documentary films) constituted another way of promoting architecture in Spain, aimed towards general public over a period of almost 40 years (1943-1981). In these state newsreels, compulsorily shown in cinemas all around the country, architecture appears mixed with other news of diverse nature. When dealing with architecture, housing is the most recurring topic; both the housing built in Spain, where new villages and urban districts emerge constantly, and the foreign housing, which the newsreel considers a symbol of modernity itself. The image of foreign housing that NO-DO newsreels transmit is heterogeneous and basically responds to four recurring types of news on the screens: Odd geometrical shapes (which are strange to the general public), new materials, new constructive techniques and installations, residential buildings set in peculiar locations or situations and exhibitions showing the progress in housing

Mixed Fattening of Steers and Lambs on Improved Grasslands in Uruguay: II. Animal Performance and Productivity

In cow-calf operations in Uruguay, mixed cattle and sheep grazing on rangelands is predominant, while fattening is a specialised process. Within certain limits of the lamb/steer ratio and stocking rate, a complementary grazing effect occurs under mixed grazing, improving net results (Nolan & Connolly, 1977; Risso et al., 2002). These trials characterise animal performance under such management