Energy modulated electron therapy (EMET) is a promising treatment modality that has the fundamental capabilities to enhance the treatment planning and delivery of superficially located targets. Although it offers advantages over x-ray intensity modulated radiation therapy (IMRT), EMET has not been widely implemented to the same level of accuracy, automation, and clinical routine as its x-ray counterpart. This lack of implementation is attributed to the absence of a remotely automated beam shaping system as well as the deficiency in dosimetric accuracy of clinical electron pencil beam algorithms in the presence of beam modifiers and tissue heterogeneities. In this study, we present a novel technique for treatment planning and delivery of EMET. The delivery is achieved using a prototype of an automated "few leaf electron collimator" (FLEC). It consists of four copper leaves driven by stepper motors which are synchronized with the x-ray jaws in order to form a series of collimated rectangular openings or "fieldlets". Based on Monte Carlo studies, the FLEC has been designed to serve as an accessory tool to the current accelerator equipment. The FLEC was constructed and its operation was fully automated and integrated with the accelerator through an in-house assembled control unit. The control unit is a portable computer system accompanied with customized software that delivers EMET plans after acquiring them from the optimization station. EMET plans are produced based on dose volume constraints that employ Monte Carlo pre-generated and patient-specific kernels which are utilized by an in-house developed optimization algorithm. The structure of the optimization software is demonstrated. Using Monte Carlo techniques to calculate dose allows for accurate modeling of the collimation system as well as the patient heterogeneous geometry and take into account their impact on optimization. The Monte Carlo calculations were validated by comparing them against output measurements with an ionization chamber. Comparisons with measurements using nearly energy-independent radiochromic films were performed to confirm the Monte Carlo calculation accuracy for 1-D and 2-D dose distributions. We investigated the clinical significance of EMET on cancer sites that are inherently difficult to plan with IMRT. Several parameters were used to analyze treatment plans where they show that EMET provides significant overall improvements over IMRT.

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This thesis is concerned with the interaction of a finely focussed light beam and a semiconductor. The object of the work is to develop a consistent theory which explains the formation of both the optical beam induced current and photoluminescence signals with a view to using these techniques to characterize semiconductor materials. Here we extend previous theories by considering a light beam which is focussed through a lens of finite numerical aperture. Expressions are derived which give the distribution of excess minority carriers injected into a semi-infinite semiconductor by the focussed light beam. The injected minority carrier distribution is then used to predict the imaging properties of the optical beam induced current and photoluminescence techniques when used to image electrically active defects in semiconductors. High resolution scanning photoluminescence images of indium phosphide are presented showing a resolution which is in good agreement with theory. The form of both the steady state and time dependent optical beam induced current in Schottky barrier diodes, planar junction diodes and devices where the p-n junction is perpendicular to the semiconductor surface is derived. Various methods are suggested for measuring the minority carrier diffusion length and lifetime. An extension to previous analyses is given by considering the effect of scanning the light beam, at some arbitrary velocity, on the form of the optical beam induced current collected by a p-n junction either parrallel or perpendicular to the semiconductor surface. It is also shown how the scan speed can effect the imaging of electrically active defects producing a contrast function which is asymmetric and reduced in magnitude. An analysis of the photoluminescence signal generated from a semi-infinite semiconductor by a finely focussed light beam is given. Various methods based on the photoluminescence technique are suggested for measuring the minority carrier lifetime.

Cancer therapy with high-energy particles has proved to be beneficial over the last 10 years. Protons are regarded as being more advantageous because of their distinctive physical depth dose distribution that allows dose conformation to the tumor while sparing normal tissue. In this study, the relative biological effectiveness (RBE) values for the 200-MeV clinical proton beam at iThemba LABS were measured at strategic positions along a 5 cm Spread-Out-Bragg-Peak (SOBP). RBE values were evaluated at the initial plateau of the virgin beam (24.2 mm in Perspex), and at the middle part, distal part and distal edge (12.4% max. dose) along the SOBP (depth in Perspex= 161.4, 181.3 and 207.7 mm respectively). Biological systems used were Chinese hamster ovary cells (CHO-Kl) for both cell survival and micronuclei frequencies as well as human T-lymphocytes for micronuclei frequency analysis. (60)^Co y-irradiation served as a reference. Cell survival measurements yielded RBE values of 1.17 at the distal part and 1.62 at the distal edge (12.4 max. dose). For micronuclei analysis, a limiting RBEap+ay value of 1.3 at the distal part was observed. Using T-lymphocytes, RBEap+/ay values calculated were 2.1, 2.7 and 3.2 at the middle part, distal part and distal edge, respectively. These results show an increase in RBE with depth of penetration and are explained by an increase in ionization density at the end of the SOBP. This is influenced by a high fraction of low-energy protons at that position. Protons were found to be most potent per unit dose towards the end as they slow down to a complete stop. It is recommended that an RBE value slightly greater than the current 1.1 be applied in therapy. Also, that the less steep biological effective depth dose curve be taken into account when dose planning. / Thesis (MSc. ARST) North-West University, Mafikeng Campus, 2003

Printed lens antennas offer the possibility of realizing shaped beam patterns using no more complexity than is required for pencil beam patterns. Shaped beam patterns can be obtained by appropriately determining the complex transmission coefficient required for each cell (or element) of the printed lens, taking into account the varying feed field over the input surface of the lens. Certain ranges of transmission coefficient amplitude and phase are undesirable (eg. too low an amplitude implies a large reflection at the lens input surface). It would be preferable to constrain the range of values that the transmission coefficient can take as an integral part of the lens synthesis procedure, and thus the transmission coefficient itself needs to be the synthesis variable. In this thesis a synthesis technique for doing this is developed based on the method of generalized projections, modified to “operate” in the space of transmission coefficients. This makes it possible to immediately perceive what influence constraints on the actual transmission coefficients have on the possible radiation pattern performance. In addition, an approach that allows one to constrain the transmission coefficient to values that must be selected from an available database of transmission coefficients is incorporated into the synthesis technique.

The structural behaviour of simply supported reinforced concrete (R.C.) beams strengthened in flexure by externally bonded steel or fibre reinforced plastic (FRP) plates has been investigated. A novel theoretical model coupled with simple (hence, practical) procedure(s) for designing such beams against premature plate peeling failure has been developed. The theoretical model and the design procedures have been validated by an extensive number (169) of mainly large-scale test data (using steel or FRP plates) from other sources. The effects of variations in the magnitude of Young's modulus for FRP plates on the potential changes in the flexural ultimate load of R. C. beams with externally bonded FRP plates, in the absence and/or presence of plate peeling, have been investigated in some detail with the theoretical predictions of various failure loads and associated modes of failure supported by an extensive number of test results from other sources. Moreover, brief theoretical parametric studies for other first order composite beam design parameters have also been carried out in order to clarify the effects of variations in such parameters on the predicted modes of failure. It has been shown (both, theoretically and by using large scale experimental data) that the load bearing capacity for a plated beam could (under certain circumstances) be significantly lower than even that for the corresponding unplated beam with the mode of failure being of an undesirable brittle nature. Such brittle failures can obviously have serious implications in practice, where this method has been used extensively for upgrading both bridges and buildings in a number of countries, with the design calculations very often not having properly accounted for the possible occurrence of premature plate peeling phenomenon, especially when FRP plates have been used. Further work in this area included a quantitative theoretical insight into the effect of pre-cracking of the beams (under service conditions) on the ultimate plate peeling load. A critical quantitative examination of a number of previously available theoretical models, as proposed by others, has also been carried out, and some of these models for predicting the plate peeling failure of R. C. beams have been shown to suffer from rather serious shortcomings.

In 2011, Roger Xu (UToronto) carried out an experimental study to investigate shear reinforcement ratios required to cause crushing of diagonal struts in high-strength reinforced concrete I-beams. Xu’s experimental results were found to be inconclusive due to detailing issues resulting in flange splitting and web blow-out. This thesis outlines an experimental test programme completed in Spring 2012 to mitigate the issues encountered by Xu. Through experimental observation, data acquisition, and numerical analysis, the test program described in this thesis is shown to overcome the aforementioned issues. The study is expanded upon with an additional test series of rectangular beams aimed to examine the applicability of the maximum shear capacity provision of the Canadian Standards Association (CSA) A23.3-04 design standard. Test data suggests that the 0.25fc'bwdv upper limit for shear reinforcement used in CSA A23.3-04 cannot be reliably attained when using high strength concrete.

In 2011, Roger Xu (UToronto) carried out an experimental study to investigate shear reinforcement ratios required to cause crushing of diagonal struts in high-strength reinforced concrete I-beams. Xu’s experimental results were found to be inconclusive due to detailing issues resulting in flange splitting and web blow-out. This thesis outlines an experimental test programme completed in Spring 2012 to mitigate the issues encountered by Xu. Through experimental observation, data acquisition, and numerical analysis, the test program described in this thesis is shown to overcome the aforementioned issues. The study is expanded upon with an additional test series of rectangular beams aimed to examine the applicability of the maximum shear capacity provision of the Canadian Standards Association (CSA) A23.3-04 design standard. Test data suggests that the 0.25fc'bwdv upper limit for shear reinforcement used in CSA A23.3-04 cannot be reliably attained when using high strength concrete.