64 research outputs found
Magnetic resonance imaging (MRI) guided radiotherapy for prostate cancer
No full textRadiotherapy to the prostate involves increasingly sophisticated delivery techniques and changing fractionation schedules. Magnetic resonance imaging (MRI) guided radiotherapy allows daily adaptive replanning and can improve accuracy. Integrating an MRI scanner and linear accelerator (linac) for the MRLinac harnesses the advantages of MRI for intrafractional imaging with the potential for tumour tracking, gated treatment and adaptive radiotherapy. I initially focus on pre-clinical research to model the benefits of the addition of MRI in radiotherapy planning and treatment. I firstly examine prostate motion, as assessed by automatic tracking of fiducials, confirming previously published data on the intrafraction motion of the prostate and setting the scene for the need for adaptive radiotherapy. Further work concentrates on the stages of adaptive treatment and the challenges involved. With more data emerging on the safety and benefits of extreme hypofractionated prostate schedules, I test the feasibility of planning prostate SBRT for the MR-Linac. I assess the factors for online and real-time imaging including the optimisation of MRI sequences and autosegmentation. My final two chapters focus on the clinical MR-Linac workflow. I describe the first-in-man study 'Prostate Radiotherapy Integrated with Simulataneous MRI' (PRISM) trial, treating patients requiring radical prostate radiotherapy on the MR-Linac. There is a complex workflow involved in delivering online adaptive imaging based on the daily anatomy, which has been feasible and in the limited number of patients discussed, not associated with increased toxicity compared to standard treatment. Finally, looking ahead to the changes required to make the workflow more efficient whilst maintaining accuracy, I present data on the accuracy of treatment radiographer and automated propagated contours. This thesis takes each of these steps in turn to assess the feasibility of this novel treatment delivery, which has the potential to optimise fractionation schedules and improve target dose whilst reducing toxicity from treatment
Analysis of loco-regional failures in head and neck cancer after radical radiation therapy
No full textObjectives: To investigate the anatomical distribution of loco-regional treatment failures (LRF) in patients with head and neck squamous cell carcinoma (HNSCC) in relation to clinical target volume (CTV) delineation.
Materials and methods: 56 patients with LRF were retrospectively identified. Patients were previously treated with radical intensity modulated radiotherapy (IMRT) +/- chemotherapy. Target volumes include gross tumour volume (GTV), its volumetric expansion of 10 mm (GTV-HD), CTV high dose (CTV-HD) delineated by anatomic expansion from GTV and CTV low dose (CTV-LD) defined to receive a prophylactic dose. LRF were evaluated by PET-CT or CT scan.
Materials and methods: We analysed the association between sites of LRF and target volumes and dosimetry, using image co-registration. Based on percentage of volume that received 95% of prescribed dose, LRF were classified as in-field, marginal or out-field.
Results: Median interval time from end of treatment to LRF was 186 days. 65 (95.6%) LRF were classified as in-field. Considering primary target volumes, 40 (58.8%) LRF occurred inside GTV, 13 (19.1%) in GTV-HD and 7 (10.3%) in CTV-HD. The overall 1-year and 2-year post-failure survival (PFS) was 45.8% and 24.2%, respectively. Post radiation LRF managed with salvage surgery had a significantly higher median PFS when compared with palliative treatments (p = 0.003).
Conclusions: The majority of LRF occurred within GTV/GTV-HD, suggesting it is safe to reduce the CTV to a volumetric expansion. Given the low incidence of geographical misses, future studies should be directed towards dose escalation of high-risk volumes. Potential reduction of RT-related toxicity with volumetric expansion could facilitate salvage surger
The Sri Lankan Debt Crisis: Is there a way out?
No full textThis thesis deals with the current debt crisis is Sri Lanka, which was brought about by rapid development following the end of the civil war, and how best to prevent future debt crises by providing recommendations to policy makers. This thesis makes use of two models, the Balance-of-Payments (BOP) Constrained growth model, and the Flying Goose Model (FGM) of development which was observed in East Asian countries during their fast-paced growth period. The BOP model is used to identify industries within Sri Lanka’s economy which have a high income elasticity of demand by the rest of the world. The results of the data analysis find that Sri Lanka has a high income elasticity of demand in the machinery and chemical sectors with in the manufacturing industry. The Sri Lankan economy is also diagnosed in the context of the FGM to understand in what stage of the FGM Sri Lanka is in, by means of carrying out non-parametric analysis on the FDI per capita, the trade dependence ratio, the revealed comparative advantage index and other economic parameters. From the evidence presented by the two models, policy recommendations go in the direction of promoting selective industrial policy, in order to enhance the growth of these targeted industries identified by the BOP model through means of accelerating the Flying Goose Model of development
Inverse membrane problems in elasticity
No full textThe inverse elasticity problem of determining the undeformed, deflated, configuration of a nonlinear elastic membrane, given the deformed configuration enclosing an incompressible fluid under known pressure, is considered. It is shown that, in practical cases, it is enough to determine only the undeformed metric tensor, and it is also shown how the two- and three-dimensional cases are fundamentally different. For the three-dimensional case, we set up and classify the partial differential equations to be solved, prove existence of an undeformed state given an undeformed metric and study the axisymmetric case in detail. © The author 2009. Published by Oxford University Press; all rights reserved
Health systems research training enhances workplace research skills: a qualitative evaluation.
No full textINTRODUCTION: In-service education is a widely used means of enhancing the skills of health service providers, for example, in undertaking research. However, the transfer of skills acquired during an education course to the workplace is seldom evaluated. The objectives of this study were to assess learner, teacher, and health service manager perceptions of the usefulness, in the work setting, of skills taught on a health systems research education course in South Africa and to assess the extent to which the course stimulated awareness and development of health systems research in the work setting. METHODS: The education course was evaluated using a qualitative approach. Respondents were selected for interview using purposive sampling. Interviews were conducted with 39 respondents, including all of the major stakeholders. The interviews lasted between 20 and 60 minutes and were conducted either face to face or over the telephone. Thematic analysis was applied to the data, and key themes were identified. RESULTS: The course demystified health systems research and stimulated interest in reading and applying research findings. The course also changed participants' attitudes to routine data collection and was reported to have facilitated the application of informal research or problem-solving methods to everyday work situations. However, inadequate support within the workplace was a significant obstacle to applying the skills learned. DISCUSSION: A 2-week intensive, experiential course in health systems research methods can provide a mechanism for introducing basic research skills to a wide range of learners. Qualitative evaluation is a useful approach for assessing the impacts of education courses
Durability Performance of Concrete Structures Built with Low Carbon Construction Materials
No full textAbstractHere, we demonstrate the feasibility of industrial application of low carbon supplementary cementitious materials (i.e. geopolymer concrete) by investigating the durability performance of eight years aged reinforced geopolymer concrete structure exposed to ambient environment. The corrosion performance of reinforcement bar in concrete and permeability characteristic of cover concrete is investigated by using non-destructive techniques. The results reveal that the reinforcement in geopolymer concrete exhibits higher corrosion risk in atmospheric environment and this attributes to the deterioration of long term durability performance for geopolymer concrete
Interpretation of the loading/wetting behaviour of compacted soils within the MPK framework: Part II Dynamic compaction
No full textDynamic compaction is commonly used to construct structural fills for various geo-infrastructures. Current practice is to specify a minimum dry density and moisture content criterion to be used in the field on the basis of Proctor compaction carried out in the laboratory. Nonetheless, we still do not have practical methods for predicting the compacted clay behaviour under expected mechanical and environmental loadings. Current theories are difficult to apply in practice due to difficulty in determining the necessary parameters. In this paper, the recently developed MPK framework is extended to cover dynamically compacted soils, with significant supporting experimental evidence. Two types of soils are used; lightly reactive kaolin and reactive Merri Creek clay. Since the compaction stress was unknown for dynamic compaction, recompression of soil specimens from compacted soil was used to establish the Loading Wetting State Boundary Surface (LWSBS). Independent tests showed that the framework can predict well the behaviour of compacted soils under loading/unloading and yielding, collapse during wetting, change of loading yield stress after wetting, and swelling pressure development during constrained wetting. The value of the approach is that the testing methods are straight-forward, do not require specialised equipment and the testing times are much shorter. In addition, the uncertainty that laboratory dynamic compaction may not relate directly to field roller compaction can be addressed with the developed framework. Soil specimens obtained from field soil pads compacted by actual rollers can be used to establish the LWSBS. This information will allow the prediction of the likely behaviour of field compacted fills under expected environmental and mechanical loadings under one-dimensional conditions. Extension to triaxial conditions would require further experimental work and theoretical modelling.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
An equation to predict maximum pipe stress incorporating internal and external loadings on buried pipes
No full textPipelines used for water and other services are very important lifelines in modern society. As many of these pipelines have been laid sometime in the last century or earlier, in most cases their condition has deteriorated primarily by electro-chemical and (or) micro-biological corrosion. This paper describes the application of 3-D finite element method to analyse a buried pipe subject to external and internal loads. Firstly, the finite element model is validated against the data from field tests. Subsequently, the results of these 3-D finite element analyses are used to develop a closed-form expression to predict maximum stresses in pipes of different sizes buried in different soil types. Having obtained a good agreement between the proposed model outcomes and 3-D FE results, the proposed model has been validated against the field test data under different internal and external loadings. The verified outcomes of the model revealed that it can be used to predict maximum stresses without conducting full scale finite element analyses, which often requires specific computational resources and computational skills. Further, the proposed model can be used in probabilistic analyses where a large number of calculations need to be carried out to account for uncertainty of the input variables.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Charging Infrastructure and Grid Integration for Electromobility
No full textElectric vehicle (EV) charging infrastructure will play a critical role in decarbonization during the next decades, energizing a large share of the transportation sector. This will further increase the enabling role of power electronics converters as an energy transition technology in the widespread adoption of clean energy sources and their efficient use. However, this deep transformation comes with challenges, some of which are already unfolding, such as the slow deployment of charging infrastructure and competing charging standards, and others that will have a long-term impact if not addressed timely, such as the reliability of power converters and power system stability due to loss of system inertia, just to name a few. Nevertheless, the inherent transition toward power systems with higher penetration of power electronics and batteries, together with a layer of communications and information technologies, will also bring opportunities for more flexible and intelligent grid integration and services, which could increase the share of renewable energy in the power grid. This work provides an overview of the existing charging infrastructure ecosystem, covering the different charging technologies for different EV classes, their structure, and configurations, including how they can impact the grid in the future.</p
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