The complexity of radiation therapy delivery has increased over the years due to advancements in computing and technical innovation. A system of dose delivery verification has the potential to catch treatment errors and therefore improve patient safety. The goal of this thesis was to create a portal image-based in vivo dose reconstruction model for volumetric modulated arc therapy (VMAT) deliveries, specifically for stereotactic body radiation therapy (SBRT). This model-based approach should be robust and feasible within a clinical setting. VMAT involves the modulation of dose rate, gantry speed, and aperture shaping while the treatment gantry (i.e., x-ray beam) rotates about the patient. In this work, portal images were acquired using an amorphous silicon electronic portal imaging device (a-Si EPID). A geometrical characterization of the linear accelerator (linac) during VMAT delivery was performed. An angle adjustment method was determined which improves each EPID’s angular accuracy to within ±1° of the true physical angle. SBRT delivers large doses over fewer fractions than conventional radiotherapy, therefore, any error during an SBRT delivery will have a greater impact on the patient. In this work, a robust, model-based SBRT-VMAT dose reconstruction verification system using EPID images was developed. The model was determined to be clinically feasible. The accuracy of a 3D in vivo dose reconstruction, using all the EPID images acquired during treatment, is sensitive to the chosen frame averaging per EPID image: the greater the frame averaging, the larger the reconstruction error. Optimization of the EPID frame averaging number as a function of average linac gantry speed and dose per fraction were determined. The EPID-based in vivo dose reconstruction model for SBRT-VMAT developed here was determined to be robust, accurate, and clinically feasible as long as adjustments were made in order to correct for EPID image geometrical errors and frame-averaging errors. / May 2016

Thesis (MMed)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Radiotherapy in the Management of Carcinoma of the Vulva in Human Immune-Deficiency Virus (HIV) Positive and Negative Patients: An Institutional Experience. Opakas J. Department of Medical Imaging and Clinical Oncology, Division of Radiation and Clinical Oncology, Tygerberg Academic Hospital and the University of Stellenbosch Background: Radiotherapy and chemotherapy are integral parts of the effective and optimal management of patients with vulva cancer, especially when initiated early in the course of this disease. Often, surgical resection alone cannot effect total removal of the tumour or may not be feasible. Human Immune-Deficiency Virus (HIV) infection has been an epidemic in sub-Saharan Africa. Highly Active Antiretroviral Therapy (HAART) is available in public health facilities in the region to arrest and control HIV infection, delaying the progression to AIDS and death. Infection with HIV has now been transformed into a manageable, chronic disease and this has allowed patients to live longer, healthier and more productive lives. Human Immune-Deficiency Virus (HIV) infection may further complicate the management of vulva cancer disease as patients are immunocompromised and may have difficulty in completing treatments prescribed. This study aims to identify and assess the outcomes, tolerances, toxicities and factors influencing treatment completion in both HIV positive and negative patients with vulva cancer treated at Tygerberg Academic Hospital. Study Design and Methods: This is a retrospective, observational, cross-sectional review of the factors influencing the completion of radical radiotherapy in the treatment of locally advanced cancer of the vulva. Patients are classified as either HIV positive or HIV negative. The period of the study was between 1st. January 2007 and 31st December 2012 and it was conducted at the Division of Radiation Oncology, Tygerberg Academic Hospital, Cape Town, South Africa. All the HIV positive patients were already on antiretroviral therapy at the outset. The disease and treatment characteristics are described as well as toxicities of treatment of patients undergoing radiotherapy and chemo-radiation. Treatment completion for the two groups is evaluated. The toxicities that led to treatment interruptions for these groups are also listed. Results: Of the 68 patients screened, 25 met inclusion criteria; of these patients, seven (28%) were HIV positive while the other 18 (72%) were negative. Vulva cancer patients infected with HIV presented at a younger age and with more locally advanced tumours compared to HIV negative patients. There is no statistically significant difference between the two groups in treatment completion rates and tumour failure rates. Conclusion: This retrospective study concludes that HIV positive patients with vulva cancer presented with a more locally advanced disease and at a younger age when compared to HIV negative patients. There was no statistically significant difference in overall therapeutic outcomes although cutaneous toxicities were more pronounced in the HIV positive subset. Chemo-radiotherapy sequentially or concurrently can be regarded as a standard of care in both HIV positive and negative patients provided that the HIV patients are on antiretroviral therapy. / AFRIKAANSE OPSOMMING: Nie beskikbaar

published_or_final_version / Clinical Oncology / Doctoral / Doctor of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Nursing Studies / Master / Master of Nursing

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