Background: In treatment planning for intensity-modulated proton therapy (IMPT), we aim to deliver the prescribed dose to the target yet minimize the dose to adjacent healthy tissue. Mixed-integer programming (MIP) has been applied in radiation therapy to generate treatment plans. However, MIP has not been used effectively for IMPT treatment planning with dose-volume constraints. In this study, we incorporated dose-volume constraints in an MIP model to generate treatment plans for IMPT. Methods: We created a new MIP model for IMPT with dose volume constraints. Two groups of IMPT treatment plans were generated for each of three patients by using MIP models for a total of six plans: one plan was derived with the Limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) method while the other plan was derived with our MIP model with dose-volume constraints. We then compared these two plans by dose-volume histogram (DVH) indices to evaluate the performance of the new MIP model with dose-volume constraints. In addition, we developed a model to more efficiently find the best balance between tumor coverage and normal tissue protection. Results: The MIP model with dose-volume constraints generates IMPT treatment plans with comparable target dose coverage, target dose homogeneity, and the maximum dose to organs at risk (OARs) compared to treatment plans from the conventional quadratic programming method without any tedious trial-and-error process. Some notable reduction in the mean doses of OARs is observed. Conclusions: The treatment plans from our MIP model with dose-volume constraints can meetall dose-volume constraints for OARs and targets without any tedious trial-and-error process. This model has the potential to automatically generate IMPT plans with consistent plan quality among different treatment planners and across institutions and better protection for important parallel OARs in an effective way.

These days, the cooling of new generation electronic servers is a challenge due to the immense heat generated by them. In order to avoid overheating caused by the important rise in temperature appropriate cooling procedures must be used in order to meet the thermal requirement. The current study aims at addressing the issue of overheating in this field, and focuses on the thermal management of electronic devices modelled as a discrete heat sources (mounted in a rectangular cavity) with uniform heat flux applied from the bottom. A review of the literature published regarding the convective heat transfer from heated sources as well as a thorough background on the theory of the cooling of discrete sources by forced convection in rectangular channel is provided in this study. It was showed that the heat transfer performance in channel is strongly influenced by the geometric configurations of heat sources. Therefore, the arrangement and geometric optimisation are the main considerations in the evaluation of thermal performance. Unlike experimental methods that were carried out widely in the past, which provided less cost-effective and more time-consuming means of achieving the same objective, in this study we first explore the possibilities and the advantages of using the CD-adapco's CFD package Star-CCM+ to launch a three dimensional investigation of forced convection heat transfer performance in a channel mounted with equidistant heatgenerating blocks. Numerical results were validated with available experimental data, and showed that the thermal performance of the heat transfer increases with the strength of the flow. The second objective was to maximise the heat transfer density rate to the cooling fluid and to minimise both the average and the maximum temperature in the channel by using the numerical optimisation tool HEEDS/Optimate+. The optimal results showed that better thermal performance was not obtained when the heated sources followed the traditional equidistance arrangement, but was achieved with a specific optimal arrangement under the total length constraint for the first case. Subsequently, for the second case study, on the volume constraints of heat sources, the results proved that optimal configurations that maximise the heat transfer density rate were obtained with a maximum of either the height-to-length ratio or the height-to-width ratio. It was concluded that the heat transfer rate to the cooling fluid increases significantly with the Reynolds number and the optimal results obtained numerically are found to be fairly reliable. / Dissertation (MSc)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / MSc / Unrestricted