4. Electronic Theses and Dissertations (ETDs) - Faculties submissions

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Optimization of Prostate Plan in a Pelvic Prosthesis Phantom
(University of the Witwatersrand, Johannesburg, 2024-09) Dumela, Khombo Eunice; Oderinde, Oluwaseyi M.; Usman, IyaboT.
Background: An increasing number of elderly prostate cancer patients with high-density material hip prosthesis are referred for external beam Radiotherapy (EBRT). Radiation treatment of pelvis cancer patients with high-density hip prosthesis needs special attention because of the artifacts created in the computed tomography (CT) field of view and the radiotherapy dosimetry challenges. The accuracy of the treatment planning dose calculation algorithms determines the accuracy of the dose delivered to the patient during radiation therapy. However, the most available algorithms do not accurately model the absorption of high-density metals’ scattering properties and underestimate the resulting dose perturbations. Aim: This study aims to optimize the dose distribution of prostate 3D conformal treatment, intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) in an in-house metallic hip prosthesis phantom. Methods and materials: In this study, an ionization chamber and Gafchromic (EBT3) films were used to physically measure the prostate point dose in an in-house pelvic phantom. The pelvic phantom was irradiated on the Linac with four static fields, namely, (1) anterior field, (2) posterior field, (3) right lateral field passing through the bone of the normal hip and (4) left lateral passing through the hip prosthesis. IMRT and VMATs plans were also generated on the phantom. The phantom was also irradiated with IMRT and VMATs plan. The use of single arc versus two arcs with avoidance sector were also evaluated. The phantom consists of different materials; Nylon-12 (a solid water-equivalent material) to simulate the prostate with a central cavity to accommodate an ionization chamber and film, superflab gel bolus to simulate human soft tissue, dental wax to simulate human soft tissue, bone anatomy for the right hip and a titanium implant to replace the bony structure of the left hip. For the static fields, an in-house pelvic phantom was simulated using the EGSnrc Monte Carlo code, and 6 and 15 MV photon energies were employed as in an experimental setting. The prostate point doses computed by the Treatment Planning System (TPS), measured using ionisation chamber, and Gafchromic EBT3 film were compared with the prostate point doses simulated by Monte Carlo code. Results and discussion: The novel phantom was constructed using superflab gel bolus, Nylon-12, dental wax, pig bone insert and a titanium alloy hip replacement. The radiological equivalence of the superflab gel bolus and dental wax was determined employing linear attenuation coefficients and then compared to an RW3 Solid water phantom. EGSnrc Monte Carlo (MC) code was used in this study. Before using Monte Carlo codes, they need to be validated by comparing the Linear accelerator Monte Carlo simulated dose distribution with the experimental data measured in a Linear accelerator using water and ionization chamber for 6 MV and 15 MV photon beams of different field sizes. The EGSnrc dose distributions were compared with the experimental measurements using a gamma analysis, employing a 2 %/2 mm distance-to-agreement criterion. The EGSnrc Monte Carlo calculated dose distribution agreed well with experimental measurements within 2 %. The MC beam model was then used to compute the dose distribution in an in-house pelvic phantom. The comparison of the measurements between the TPS calculated prostate point dose and ionization chamber for the 6 MV and 15 MV photon beams was: anterior (gantry 0°) 1.8 % and -0.5 %; posterior (gantry 180°) 1.7 % and -0.2 %; left lateral (gantry 90°) 6.3% and 4.2 %; right lateral (gantry 270°) -2.2 % and -2.1 % respectively. Results obtained for Gafchromic EBT3 film measured doses were: anterior 2.3 % and 1.3 %; posterior -0.9 % and 0.2 %, left lateral 4.5 % and 3.5 %; right lateral -2.1 % and -2.5%, for the 6 MV and 15 MV photon beams, respectively. Consequently, results obtained for comparison of TPS, ion chamber and Film with MC simulated doses were: anterior 3.9 %, -2.1 and -1.6% %; posterior 1.8 %, -0.1% and -2.7 %; left lateral -0.2 %, 6.5 % and 4.7 %; right lateral 0.4 %, -2.6% and -2.5 %, for the 6 MV photon beam. And for 15 MV photon beam the results were: anterior 1.9 %, -3.8 and -0.6%; posterior 2.0 %, -2.3 % and -2.2 %; left lateral 0.5 %, 3.7 % and 2.9 %; right lateral 0.4 %, -2.4 % and -2.9 %. Monte Carlo simulations and film measurements have a statistically significant difference of p<0.001, with the film measurements having a higher value than MC simulations except on the left lateral field. Monte Carlo simulations and ionization chamber measurements also show a significant difference of p<0.001, with the ionization chamber having a higher value than the MC simulation, except for the left lateral field passing through the hip prosthesis. The comparison of the measurements between the TPS calculated prostate point dose with ionization chamber and Gafchromic EBT3 film for the 6 MV IMRT plan of the beam passing through the prosthesis was 2.2 % and 3.3%, respectively. While the IMRT plan with avoided beam was 1.9 % and 3.1% for ionization chamber and Gafchromic EBT3 film, respectively. The comparison of the measurements between the TPS calculated prostate point dose for the 6 MV VMAT plan without avoiding for the beam passing through the prosthesis was 1.1 % and 2.2 % for ionization chamber and Gafchromic EBT3 film, respectively. While for VMAT plan with avoided sector as 3.0 % and 4.0% for ionization chamber and Gafchromic EBT3 film, respectively. The test suggested a significant difference of p=0.0001 between the distribution of film measurements and TPS calculated dose. Meanwhile, for ionization chamber measurements and TPS calculated dose; the test indicated a significant difference between ion chamber measurements and TPS calculated dose with a significant level of less than 0.001. in addition, MC simulated dose and TPS calculated dose; the test shows a percentage difference of -0.2 % and 0.5 % for 6 MV and 15 MV photon beams in the lateral field that passes through the prosthesis. The test indicated the significant difference of p=0.001 which is slightly lower compared to the other comparisons. Conclusion: The dual dosimetric pelvic prosthesis phantom is easy to assembly and is more convenient for second dose check for patients with hip prostheses. Through the use of the pelvic phantom, it was possible to measure the prostate point dose using ionization chamber and films. The TPS overestimated the prostate point dose because the treatment planning algorithm could not accurately determine the CT number and the electron density of the prosthesis due to the limitation on the CT scanner. The maximum deviation calculated in this study for TPS, ionization chamber Gafchromic EBT3 films when compared to Monte Carlo simulated dose comes from the lateral fields passing through the prosthesis for both 6 MV and 15 MV photon beams.
Experiences of social workers regarding managing workload during COVID-19 pandemic: A study at the Department of Social Development in Roodepoort
(University of the Witwatersrand, Johannesburg, 2024) Mambabada, Tshiwela Portia
The aim of this study was to explore experiences of the Department of Social Development (DSD) social workers when managing their workload during the COVID-19 pandemic. This is a qualitative study that employed exploratory case study research design to understand the experiences of participants in their everyday life within their workplace. The researcher utilised a non-probability purposive sampling procedure to select participants. Fifteen (15) participants were recruited from Roodepoort’s DSD in South Africa. The researcher used a semi-structured interview schedule as the data collection tool. Data was collected on one-on-one basis, face-to- face with participants. The researcher was interested in utilising a thematic analysis to analyse the collected data. The study offers insights into how social workers’ workload at DSD changed as a result of the COVID-19 pandemic. The insights are used to make recommendations for future disaster plans to support social workers and the clients that they serve within DSD. Fundings show that Roodepoort DSD social workers faced higher caseload in foster care. This was as a result of a shortage of social workers and limited resources during the COVID-19 pandemic. These social workers also faced changes that were brought about by the pandemic, such as the shortage of personal protective equipment and they had to adopt hybrid work to provide services to clients virtually. They experienced poor mental health due to increased workload, stress, and burnout. Their coping strategies were based on exercising and employee assistance programmes.
Investigating the performance of South African children from an under-resourced background on selected verbal subtests of the WISC-V and SSAIS-R
(University of the Witwatersrand, Johannesburg, 2024) Rampai, Tsholofelo; Vorster, Adri
Given the South African context and the scarcity of valid and reliable individual intelligence measures to assess the intellectual functioning of a broad spectrum of children from different socioeconomic, cultural, and linguistic backgrounds, continued research must be done on the utility, validity, and reliability of available measures. Taking this into consideration, the present study aimed to investigate and compare the performance of a sample of South African children who predominantly speak English as a Second Language (ESL) and who come from an under-resourced background on selected verbal subtests of the Wechsler Intelligence Scale for Children – Fifth Edition (WISC-V) and the Senior South African Individual Scales – Revised (SSAIS-R). In addition, the study investigated the internal consistency reliability and concurrent validity of these subtests in the present sample. The children's biographical information was obtained from a demographic questionnaire. The sample consisted of 58 participants (N= 58) from grades 4 to 7 living and developing in under-resourced contexts. Based on the data spread, parametric statistics in the form of a paired t-test, Pearson’s correlation coefficient, and Spearman-Brown split-half formula were used to address the aims of the study and answer the research questions. The findings highlighted the different factors that might influence assessment results in South Africa, particularly for children from under-resourced contexts. The current study can be a stepping stone for further research into the appropriateness of commonly used individual intelligence measures in under-resourced contexts, given that not all South African contexts have been investigated regarding psychological assessments and individual intelligence measures.
Counting Reward Automata: Exploiting Structure in Reward Functions Expressible in Decidable Formal Languages
(University of the Witwatersrand, Johannesburg, 2024-07) Bester, Tristan; Rosman, Benjamin; James, Steven; Tasse, Geraud Nangue
In general, reinforcement learning agents are restricted from directly accessing the environment model. This restricts the agent’s access to the environmental dynamics and reward models, which are only accessible through repeated environmental interactions. As reinforcement learning is well suited for use in complex environments, which are challenging to model, the general assumption that the transition probabilities associated with the environment are unknown is justified. However, as agents cannot discern rewards directly from the environment, reward functions must be designed and implemented for both simulated and real-world environments. As a result, the assumption that the reward model must remain hidden from the agent is unnecessary and detrimental to learning. Previously, methods have been developed that utilise the structure of the reward function to enable more sample-efficient learning. These methods employ a finite state machine variant to facilitate reward specification in a manner that exposes the internal structure of the reward function. This approach is particularly effective when solving long-horizon tasks as it enables the use of counterfactual reasoning with off-policy learning which significantly improves sample efficiency. However, as these approaches are dependent on finite-state machines, they are only able to express a small number of reward functions. This severely limits the applicability of these approaches as they cannot model simple tasks such as “fetch a coffee for each person in the office” which involves counting – one of the numerous properties finite state machines cannot model. This work addresses the limited expressiveness of current state machine-based approaches to reward modelling. Specifically, we introduce a novel approach compatible with any reward function which can be expressed as a well-defined algorithm We present the counting reward automaton – an abstract machine capable of modelling reward functions expressible in any decidable formal language. Unlike previous approaches to state machine-based reward modelling, which are limited to the expression of tasks as regular languages, our framework allows for tasks described by decidable formal languages. It follows that our framework is an extremely general approach to reward modelling – compatible with any task specification expressible as a well-defined algorithm. This is a significant contribution as it greatly extends the class of problems which can benefit from the improved learning techniques facilitated by state machine-based reward modelling. We prove that an agent equipped with such an abstract machine is able to solve an extended set of tasks. We show that this increase in expressive power does not come at the cost of increased automaton complexity. This is followed by the introduction of several learning algorithms designed to increase sample efficiency through the exploitation of automaton structure. These algorithms are based on counterfactual reasoning with off-policy RL and use techniques from the fields of HRL and reward shaping. Finally, we evaluate our approach in several domains requiring long-horizon plans. Empirical results demonstrate that our method outperforms competing approaches in terms of automaton complexity, sample efficiency, and task completion.
Newsroom Culture and Journalistic Practice at the South African Broadcasting Corporation (SABC): An Ethnographic study
(University of the Witwatersrand, Johannesburg, 2024) Dlamini, Tula; Chiumbu, Sarah
This research sets out to examine newsroom culture and journalism practice at the South African Broadcasting Corporation (SABC). The primary objective is to understand the factors inside the SABC newsroom that impact the construction of news stories and current affairs productions. Anchored on Pierre Bourdieu’s theories of the habitus, doxa, and capital, together with Habermas’ concept of the Public Sphere, this thesis describes the newsroom culture of the SABC between 2016 and 2021 based on everyday work experiences and perspectives of news workers, managers at the broadcaster and available documents. As a secondary objective, the study explores how SABC newscasts and current affairs programming mediate news. Specifically, the content analysis of News and Current Affairs products assesses how the SABC mediated pluralist politics during the 2016 local government elections from the perspective of normative public sphere principles and examines how routines, practices, and professional values broadly impacted the broadcaster’s coverage, particularly the contested issue of ‘land’. The study is essentially a qualitative ethnography of the SABC newsrooms, although a multi-method approach is adopted to arrive at a more encompassing view of the journalistic culture of News and Current Affairs construction at the broadcaster. The 2016 period and after are interesting because these are also moments in time when the SABC newsroom was characterised by widely reported tension and editorial turmoil. The findings reveal some of the embedded structural systems in the SABC’s newsrooms, such as the role of the management hierarchy and the institutional norms, shared professional values, and routines that journalists use to achieve functional ends for the broadcaster. Furthermore, the study identifies a gap in the general scholarship of the SABC. For example, fewer studies have attempted to account for the culture and journalistic practice inside SABC newsrooms, all of which have impacted directly on the general operations of the broadcaster and execution of its PSB mandate.
The gendered barriers women face in politics: The case study of South Africa
(University of the Witwatersrand, Johannesburg, 2024) Olivier, Ursulene; De Matos Ala, Jacqueline
Women politicians face nefarious and diverse obstacles. Their voices are both needed and lacking in the halls of national decision-making. According to the 2022 Global Gender Gap Report (GGGR) the gap in global female Political Empowerment has consistently remained the largest since the first report was published in 2006. Globally women only have 22% of the Political Empowerment that men have. This research conducts a discourse and content analyses of female political representation in South Africa and whether this translates into better outcomes for gender equality in broader society. It investigates the social constructs of political hegemonic masculinity and political patronage and the role it plays in the political careers of women to reach executive level positions such as becoming a cabinet minister and president. Key findings are gender stereotypes and gender roles found in both social constructs keep women out of political power. Many women politicians also do not champion the gender equality cause in South Africa in support of political hegemonic masculinity and political patronage.
The Stratigraphy of the New Tuli Basin Fossil Sites in Zimbabwe
(University of the Witwatersrand, Johannesburg, 2024-09) Zondo, Michel; Choiniere, Jonah; Broderick, Timothy; Munyikwa, Darlington
This thesis investigated new fossil-bearing outcrops of the Mpandi Formation of Zimbabwe, exposed at Sentinel Ranch in the Tuli Basin, at sites named “Wedding Hill “and “Pimwe Hill”. The Mpandi Formation exposures at Sentinel Ranch reveal strata that were deposited in fluvial environments that occasionally experienced flooding in otherwise usually dry and hot climatic conditions. These fluvial systems deposited facies that are mostly dominated by fine sediments and their facies have similarities with those found in the main Karoo Basin of South Africa. The use of borehole data helped establish the thickness of the Mpandi Formation and the explorable portion of the formation was estimated to be around 54 metres. Detrital zircons collected from main Sentinel outcrops were used to estimate the maximum depositional age of the sediments using inductively coupled plasma mass spectrometer (LA-ICPMS) methods. Although sparse, the youngest zircons in these samples yielded ages of 199.2 ± 5.1 Ma and 200.8 ± 5.8 Ma, with error bars suggesting maximum depositional ages in the earliest Jurassic or possibly the latest Triassic. A bonebed at the Wedding Hill site produced many postcranial bones of sauropodomorphs, including the articulated leg of a very large individual sauropodomorph, and the first theropod bones recorded from the Mpandi Formation at Sentinel. The discoveries improve our knowledge of the fauna diversity of the Mpandi Formation, permitting more accurate biostratigraphic correlation and enhancing our understanding of the Triassic- Jurassic interval.
Work-Family Conflict & Burnout in the face of a Pandemic as moderated by Sensory Processing Sensitivity and Social Support
(University of the Witwatersrand, Johannesburg, 2024) Ndlovu, Valerie; Pitman, Michael
Remote working has quickly become a norm in organisations in response to the COVID-19 global pandemic. This shift may have been a tough transition on some individuals as work and family spheres have been obscured by remote working where one environment is used for both leisure, domestic and professional reasons. A quantitative, non- experimental, correlational, cross- sectional study (N = 136) was conducted with employed South African participants using online self- report questionnaires. Correlation results showed a significant relationship between Work-Family Conflict (WFC) and burnout subscales, but not Family-Work Conflict (FWC) and burnout. Hierarchical Moderated regression was used to assess the data and showed that Sensory- Processing Sensitivity and Social Support did not moderate the relationship between WFC and burnout. The results show that females are more burnt out than males and as people get older, the less burnt out they are. Individuals experienced financial and fear of the unknown challenges due to the pandemic. This study offers a contribution to Human Resources on employee wellbeing and post- COVID-19 functioning.
Masculinity and its role in gender-based violence in South Africa
(University of the Witwatersrand, Johannesburg, 2024) Davhana-Ngwenya, Vhugala
This study investigates ways in which men construct masculinity and understand its role in gender-based violence. An increased interest in studying masculinity and its construction suggests that there are different ways in which men express their masculinities. 11 males over the age of 18 participated in the study. A semi-structured interview schedule was used to guide one on one interviews that were used to collect data. The interviews were recorded and transcribed for easy analysis. Thematic analysis was used to analyse the data through identifying, analysing, and reporting repeated themes. Specifically, four themes were identified in this study: (1) Constructions of traditional masculinity, (2) Construction of gender-based violence, (3) Role models and (4) Proposed interventions for gender- based violence. The findings suggest that participants have a negative view towards the traditional ideology of masculinity and conventional masculinity. For most of the participants’ influential role models were predominantly male figures who held positions of authority in their households or communities while for other media emerged as a significant role model. The participants understood the impact of GBV and its far-reaching consequences on its victims. The research will contribute to the field of psychology in the understandings of constructions of masculinity and its role in Gender Based Violence.
Psychological Challenges facing Primary School Children in Windhoek, Namibia: Perspectives of Teachers
(University of the Witwatersrand, Johannesburg, 2024) Uupindi, Victoria N.; Kasese-Hara, Mambwe
The study aimed to explore the psychological challenges that primary school children were facing through the perspectives of teachers. The study also investigated the support system that was available to mitigate these challenges both at school and in the community. Urie Bronfenbrenner’s Bio-Ecological Theory of human development was used as a theoretical framework to comprehend and discuss the findings of the study. The study employed a Qualitative Research approach using a phenomenological perspective. The data was collected from three primary schools in Windhoek Namibia, from a total of eight participants using face-to-face recorded interviews. The participants were recruited using a snowball sampling technique that allowed the researcher to network for the next participant. The findings indicated that children are indeed influenced by their surroundings, experiencing many challenges such as those associated with Covid-19, those created by home circumstances, negative behavior, emotional distress and challenges associated with their schooling such as low school performance. The study revealed that various systems like the schools, churches and community members all collaborate to help primary school children navigate through their challenges.

4. Electronic Theses and Dissertations (ETDs) - Faculties submissions

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