Optimization Of Portal Imaging Systems

Many portal imaging devices have been developed to verify the geometric accuracy of radiation therapy treatments. Portal imaging devices are used to take images of the patient during radiation therapy treatments. These images are used to detect patient positioning errors which may jeopardize the outcome of conventional and high-precision radiotherapy treatments. Unfortunately, the quality of portal images obtained with such devices is disappointing, resulting in sparse clinical use of these devices.;Researchers have been substituting various imaging components on these portal imaging systems in the hopes of optimizing portal image quality. This empirical approach has led to some successes. However, choosing imaging system components on the basis of one desirable parameter while ignoring the impact of the change on overall system performance wastes time, money, and effort. Clearly, a more efficient approach is required.;This thesis presents approaches for the optimization of both the design and use of portal imaging devices. These approaches require understanding of the fundamental physics of portal imaging, such as the size and shape of the x-ray sources of medical linear accelerators and the interaction of x-rays within typical portal imaging detectors. The use of existing portal imaging systems (i.e., portal films and video-based systems) has been optimized by finding the radiographic magnification which provides the best image quality for a particular system/linear accelerator combination. It has been found that, for portal films, radiographic magnification is undesirable. On the other hand, a radiographic magnification of 1.5-1.7 is optimal for video-based systems. Therefore, the image quality from an existing imaging system can be improved without changing the system design. The design of portal imaging systems has been optimized using a theoretical approach known as quantum accounting diagram (QAD) theory. Using this theory, a detailed analysis of a video-based portal imaging system has permitted the theoretical derivation of the detective quantum efficiency (DQE) of the imaging system. The analysis has shown that the video-based portal imaging system suffers from severe secondary quantum sinks for non-zero spatial frequencies, resulting from sub-optimal system design. Furthermore, the theoretical DQE\u27s have been compared with experimental measurements--the first experimental verification of the QAD theory. The QAD theory has been expanded to include the physical parameters involved with the human visual system and allow the computation of indices of perceived image quality. This approach enables the optimization of imaging devices using a single figure of merit, and has been used to optimize the phosphor screen thickness used by two different designs of portal imaging systems. We have demonstrated that the QAD approach allows us to predict the change in overall system performance for any modification in imaging system design. In future, we believe that this tool will be vital to the development and optimization of improved portal imaging systems for radiation therapy

Exploring adolescents’ critical thinking aptitudes when reading about science in the news

This research studies the critical thinking skills of six teenagers in their final years of high school. It looks at the way those students use a set of cognitive skills in order to analyze scientific and pseudoscientific information available in online news articles. Semi-structured interviews were conducted with six students chosen according to their results in a questionnaire about interest in science topics. Results show a large gap between participants’ use of critical thinking skills. Most of these skills were mainly used for text comprehension, evoking general knowledge, numeracy, arguments assessment and production, and life skills (open-mindedness and metacognition). The participants were often confused when they were asked to justify their stances, and when they had to compare arguments’ value. This exploratory study could lead to a better understanding of teenagers’ strengths and weaknesses in news media literacy, and the part that schools could play in helping students develop them

Individual Survival Curves Comparing Subjective and Observed Mortality Risks

In this paper, we compare individual survival curves constructed from objective (actual mortality) and elicited subjective information (probability of survival to a given target age). We develop a methodology to estimate jointly subjective and objective individual-survival curves accounting for rounding on subjective reports of perceived mortality risk. We make use of the long follow-up period in the Health and Retirement Study and the high quality of mortality data to estimate individual survival curves which feature both observed and unobserved heterogeneity. This allows us to compare objective and subjective estimates of remaining life expectancy for various groups, evaluate subjective expectations of joint survival and widowhood by household, and compare objective and subjective mortality with standard life-cycle models of consumption

Toward a better understanding of the placement of shotcrete: Nozzles and velocities

A lot of developments and improvements seen in the shotcrete industry over the last few decades have mostly arisen through the improvement of mixture designs and admixture efficiency. Unfortunately, limited efforts have been put into the modelling and optimization of one of the most important portions: the acceleration of the material through the nozzle and its subsequent travelling toward the surface. The paper first presents a clear explanation and demonstration, based on spray patterns analysis, of the differences between dry-mix and wet-mix shotcrete. It then follows with practical examples of ways to improve the technology behind the nozzle (for both processes) along with unique experimental results. The paper offers a discussion on where our efforts should be put to further reduce losses due to rebound and increase in-place shotcrete homogeneity to promote strength and durability

The effect of wood ash as a partial cement replacement material for making wood-cement panels

The aim of this study was to consider the use of biomass wood ash as a partial replacement for cement material in wood-cement particleboards. Wood-cement-ash particleboards (WCAP) were made with 10%, 20%, 30%, 40%, and 50% of wood ash as a partial replacement for cement with wood particles and tested for bending strength, stiffness, water absorption, and thermal properties. Test results indicate that water demand increases as the ash content increases, and the mechanical properties decrease slightly with an increase of the ash content until 30% of replacement. On the other hand, the heat capacity increases with the wood ash content. The WCAP can contribute to reducing the heat loss rate of building walls given their relatively low thermal conductivity compared to gypsum boards. The replacement of cement to the extent of approximately 30% by weight was found to give the optimum results

Osteopontin: an early innate immune marker of Escherichia coli mastitis harbors genetic polymorphisms with possible links with resistance to mastitis

<p>Abstract</p> <p>Background</p> <p>Mastitis is the most important disease in dairy cows and it causes significant lost of profit to producers. Identification of the genes, and their variants, involved in innate immune responses is essential for the understanding of this inflammatory disease and to identify potential genetic markers for resistance to mastitis. The progeny of dairy cows would benefit from receiving favourable alleles that support greater resistance to infection, thus reducing antibiotic use. This study aims to identify a key gene in the innate immune response to mastitis, led us to evaluate its genetic association with somatic cell score (SCS), which is an indicator of clinical mastitis, and to evaluate its impact on other traits related to milk production.</p> <p>Results</p> <p>The osteopontin transcript (<it>SPP1</it>) was identified in the somatic cells from cows experimentally infected with <it>Escherichia coli</it>. By selecting bulls with extreme estimated breeding values (EBVs) for SCS, which is an indicator of mammary gland health, four DNA polymorphisms in the <it>SPP1 </it>genomic sequence were found. Statistical analysis revealed that the SNP <it>SPP1c.-1301G>A </it>has an impact on EBV for SCS (<it>P </it>< 0.001) Using an allele substitution model, <it>SPP1c.-1251C>T</it>, <it>SPP1c.-430G>A</it>, and <it>SPP1c.*40A>C </it>have an impact on SCS whereas <it>SPP1c.-1301G>A </it>has an effect on the EBVs for milk yield (second and third lactations), fat and protein percentages (all three lactations). Analysis revealed statistically significant differences between haplotype groups at a comparison-wise level with sire EBVS for SCS for the first (<it>P </it>= 0.012), second (<it>P </it>< 0.001), and third (<it>P </it>< 0.001) lactations.</p> <p>Conclusion</p> <p>This study reports the link between DNA polymorphisms of <it>SPP1</it>, the number of milk immune cells and, potentially, the susceptibility to mastitis. These SNPs were identified by <it>in silico </it>search to be located in transcription factor recognition sites which factors are presumably involved in the Th1 immune response and in the Th2 regulation pathway. Indeed, one SNP abolished the SP1 recognition site, whereas another SNP affected the transcription binding factor IKAROS. All together, these findings support the genetic potential of these variants in terms of selection for the improvement of mastitis resistance in dairy cows.</p

Epistemic injustices and participatory research: A research agenda at the crossroads of university and community

This article presents an innovative framework to evaluate participatory research. The framework, comprising both a methodology and a self-assessment tool, was developed through a participatory approach to knowledge production and mobilisation. This process took place over the last two years as we, a multidisciplinary team made up of researchers and community-based organisation members from the Groupe de recherche et de formation sur la pauvreté au Québec, were building a scientific program on social injustices and participatory research. We argue that participatory research can help provide a university-community co-constructed response to epistemic injustices embedded within the processes of knowledge production. From our perspective, the mobilisation of knowledge from the university and the community, initiated at the earliest stages of the creation of a research team, is part of a critical approach to the academic production of knowledge. It also constitutes a laboratory for observing, understanding and attempting to reduce epistemic injustices through building bridges between team members. The article focuses on two dimensions of the framework mentioned above: (1) The methodology we established to build co-learning spaces at the crossroads of university and community-based organisations (recruitment of a coordinator to organise and facilitate the workshops, informal and friendly meetings, regular clarification of the process and rules of operation, time for everyone to express themselves, informal preparatory meetings for those who wanted them, financial compensation where required, etc.); and (2) A self-assessment tool available in open access that we built during the process to help academics and their partners engage in a reflexive evaluation of participatory research processes from the point of view of epistemic injustices. Throughout we pay particular attention to challenges inherent in our research program and our responses, and finish with some concluding thoughts on key issues that emerged over the course of two years’ research

A national survey of the availability of intensity-modulated radiation therapy and stereotactic radiosurgery in Canada

<p>Abstract</p> <p>Background</p> <p>The timely and appropriate adoption of new radiation therapy (RT) technologies is a challenge both in terms of providing of optimal patient care and managing health care resources. Relatively little is known regarding the rate at which new RT technologies are adopted in different jurisdictions, and the barriers to implementation of these technologies.</p> <p>Methods</p> <p>Surveys were sent to all radiation oncology department heads in Canada regarding the availability of RT equipment from 2006 to 2010. Data were collected concerning the availability and use of Intensity Modulated Radiation Therapy (IMRT) and stereotactic radiosurgery (SRS), and the obstacles to implementation of these technologies.</p> <p>Results</p> <p>IMRT was available in 37% of responding centers in 2006, increasing to 87% in 2010. In 2010, 72% of centers reported that IMRT was available for all patients who might benefit, and 37% indicated that they used IMRT for "virtually all" head and neck patients. SRS availability increased from 26% in 2006 to 42.5% in 2010. Eighty-two percent of centers reported that patients had access to SRS either directly or by referral. The main barriers for IMRT implementation included the need to train or hire treatment planning staff, whereas barriers to SRS implementation mostly included the need to purchase and/or upgrade existing planning software and equipment.</p> <p>Conclusions</p> <p>The survey showed a growing adoption of IMRT and SRS in Canada, although the latter was available in less than half of responding centers. Barriers to implementation differed for IMRT compared to SRS. Enhancing human resources is an important consideration in the implementation of new RT technologies, due to the multidisciplinary nature of the planning and treatment process.</p

Injustices épistémiques et recherche participative: un agenda de recherche à la croisée de l’université et des communautés

Cet article présente un cadre d’analyse innovant ancré dans le concept d’injustices épistémiques pour évaluer les recherches participatives. Composé d’une méthodologie de travail et d’un outil d’autoévaluation, ce cadre d’analyse a été développé au fil d’un processus participatif de production et de mobilisation des savoirs qui a pris place au cours des deux dernières années. L’équipe multidisciplinaire ayant entrepris ce processus est composée des chercheur-es et des représentant-es du Groupe de recherche et de formation sur la pauvreté au Québec travaillant à l’élaboration d’un programme scientifique de recherche sur les injustices épistémiques et les recherches participatives. Nous défendons que les recherches participatives peuvent contribuer à apporter des réponses coconstruites entre les milieux universitaires et communautaires à certaines injustices sociales – dans le cas présent, les injustices épistémiques – qui sont enchâssées dans les processus de production des connaissances. De notre point de vue, les recherches participatives constituent des laboratoires permettant d’observer et de comprendre la production des injustices épistémiques et, le cas échéant, d’offrir des leviers pour les réduire grâce à la construction de ponts entre les différentes personnes et les savoirs qu’elles détiennent. L’article est centré sur la présentation de deux dimensions de notre travail: (1) La méthodologie que nous avons mise sur pied pour bâtir des espaces de coapprentissage à la croisée de l’université et des organismes communautaires et (2) Un guide d’autoévaluation disponible en accès libre que nous avons bâti durant notre démarche afin d’aider les universitaires et leurs partenaires à s’engager dans une évaluation réflexive des processus participatifs de recherche du point de vue des injustices épistémiques. L’article met également de l’avant des défis inhérents à l’élaboration de ce programme de recherche ainsi que des réponses que nous avons pu leur apporter, et se termine par des réflexions sur les enjeux clés ayant émergé en cours de route