A study was done at Steve Biko Academic hospital to determine the influence that respiratory gating will have on target volumes used in radiotherapy treatment planning. The primary objective was to compare target volumes of respiratory gated scans to ungated scans and to determine whether it will be meaningful to permanently implement a 4D respiratory gating system on CT scanners in the South African public health sector and to use these images for target volume delineation in radiotherapy planning. The study consisted of three sections. In the first section, 4D respiratory gated CT images were obtained and delineated with 4D software. The full-inspiration and full-expiration phases of the gated scans were then fused to obtain ungated images which were also delineated. The gross tumor volumes (GTVs) of the gated phases were compared to the ungated GTVs, and found that on average the volumes decreased by 14.63% with a standard deviation of 7.96% when gating was applied. Yet another aim was to determine the influence that 4D imaging will have on radiotherapy treatment planning. One of the 4D study sets was imported to the XIO treatment planning system where IMRT treatment plans were created on both the gated and ungated scans. The plans conformed to the treatment aims and restrictions when clinical parameters such as DVHs were used to evaluate it. The planned target volume coverage differed by less than 1% between the gated and the ungated plans, but significant dose reductions to the OARs of up to 32.65% to the contralateral lung were recorded on the gated plan. In the second section of this study, respiratory gated CT scans were simulated by applying the breath-hold technique to lung cancer patients. The technique was applied during full-inspiration which fundamentally represents the maximum peak of the sinusoidal respiratory waveform. An ungated scan was also acquired during normal respiration. The clinical target volumes (CTVs) were identified on both scans by three oncologists and the average CTVs were compared. It was found that the CTVs decreased significantly by an average of 14.33%. Palliative patients receive parallel opposing field therapy which is planned from 2D films. It is very unlikely that these opposing field sizes will differ when gating is applied. It was therefore concluded that only radical lung patients, which was estimated to be a mere 0.03% of the total radiation therapy patient population, will benefit by implementing respiratory gating or any motion-reduction technique. For the third section of the study, respiratory gated PET scans were acquired on a PET/CT scanner to evaluate external, non-technical parameters that will influence respiratory gating. The results indicated that time and patient participation were not limiting factors. The biggest concerns however were the effectiveness of the gating system, software limitations and the gated results. These problems might be minimized with thorough training on the system. All three sections as well as the financial implications were considered to conclude that it will not be meaningful to implement 4D respiratory gating techniques in the South African public health sector Copyright / Dissertation (MSc)--University of Pretoria, 2013. / Medical Oncology / unrestricted

Spillways are hydraulic structures that allow dams to release and convey surplus water or flood from the reservoir to the downstream channel. The spillway is a safety structure that prevents the overtopping of the dam. Many dam failure disasters were due to the inadequate capacity of the spillway, which fully illustrates the prominence of spillway design. According to the control structure, spillways can be divided into gated and ungated type. The gated spillway provides better control of the managed water level and reduces the elevation of the top of the dam. Researchers have mostly used experimental models to investigate these two types of spillways in previous literature. In the past few years, following the rapid development of numerical simulation technology, there have been more studies on the numerical modeling of spillways. However, most of the literature was about ungated spillways and most of it considered the case of low head ratios, while the case with gates, especially the case of vertical plane gates, was less investigated. In this study, the hydraulic characteristics, such as velocity, pressure, and discharge coefficient, of the ungated and gated ogee spillways are investigated by means of physical and numerical models for the case of low and high head ratios. The study covered head ratios varying from 1.4 to 4.6 and the relative gate-openings varying from 0.5 to 2. The second main objective of this study was to evaluate the performance of the numerical model to simulate gated and ungated spillways. It mainly employed 2DV OpenFOAM to simulate three turbulence models (realizable k-ε, RNG k-ε, k-ω SST), and the results were compared and calibrated with the experimental results from the physical model tests performed by the author to verify the performance of the numerical model. This study aims to demonstrate that the numerical model can be used as a complementary tool to the physical model to measure the hydraulic performance of ogee spillways.

Advances in digital signal processing (DSP) and computing technology have resulted in the emergence of increasingly adaptive radar systems. It is clear that the Electronic Attack (EA), or jamming, of such radar systems is expected to become a more difficult task. The reason for this research was to address the issue of jamming adaptive radar systems. This required consideration of adaptive jamming systems and the development of a methodology for outlining the features of such a system is proposed as the key contribution of this thesis. For the first time, game-based optimization methods have been applied to a maritime counter-surveillance/counter-targeting scenario involving conventional, as well as so-called ‘smart’ noise jamming.Conventional noise jamming methods feature prominently in the origins of radar electronic warfare, and are still widely implemented. They have been well studied, and are important for comparisons with coherent jamming techniques.Moreover, noise jamming is more readily applied with limited information support and is therefore germane to the problem of jamming adaptive radars; during theearly stages when the jammer tries to learn about the radar’s parameters and its own optimal actions.A radar and a jammer were considered as informed opponents ‘playing’ in a non-cooperative two-player, zero-sum game. The effects of jamming on the target detection performance of a radar using Constant False Alarm Rate (CFAR)processing were analyzed using a game theoretic approach for three cases: (1) Ungated Range Noise (URN), (2) Range-Gated Noise (RGN) and (3) False-Target (FT) jamming.Assuming a Swerling type II target in the presence of Rayleigh-distributed clutter, utility functions were described for Cell-Averaging (CA) and Order Statistic (OS) CFAR processors and the three cases of jamming. The analyses included optimizations of these utility functions, subject to certain constraints, with respectto control variables (strategies) in the jammer, such as jammer power and spatial extent of jamming, and control variables in the radar, such as threshold parameter and reference window size. The utility functions were evaluated over the players’ strategy sets and the resulting matrix-form games were solved for the optimal or ‘best response’ strategies of both the jammer and the radar.

Advances in digital signal processing (DSP) and computing technology have resulted in the emergence of increasingly adaptive radar systems. It is clear that the Electronic Attack (EA), or jamming, of such radar systems is expected to become a more difficult task. The reason for this research was to address the issue of jamming adaptive radar systems. This required consideration of adaptive jamming systems and the development of a methodology for outlining the features of such a system is proposed as the key contribution of this thesis. For the first time, game-based optimization methods have been applied to a maritime counter-surveillance/counter-targeting scenario involving conventional, as well as so-called ‘smart’ noise jamming.Conventional noise jamming methods feature prominently in the origins of radar electronic warfare, and are still widely implemented. They have been well studied, and are important for comparisons with coherent jamming techniques.Moreover, noise jamming is more readily applied with limited information support and is therefore germane to the problem of jamming adaptive radars; during theearly stages when the jammer tries to learn about the radar’s parameters and its own optimal actions.A radar and a jammer were considered as informed opponents ‘playing’ in a non-cooperative two-player, zero-sum game. The effects of jamming on the target detection performance of a radar using Constant False Alarm Rate (CFAR)processing were analyzed using a game theoretic approach for three cases: (1) Ungated Range Noise (URN), (2) Range-Gated Noise (RGN) and (3) False-Target (FT) jamming.Assuming a Swerling type II target in the presence of Rayleigh-distributed clutter, utility functions were described for Cell-Averaging (CA) and Order Statistic (OS) CFAR processors and the three cases of jamming. The analyses included optimizations of these utility functions, subject to certain constraints, with respectto control variables (strategies) in the jammer, such as jammer power and spatial extent of jamming, and control variables in the radar, such as threshold parameter and reference window size. The utility functions were evaluated over the players’ strategy sets and the resulting matrix-form games were solved for the optimal or ‘best response’ strategies of both the jammer and the radar.