A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in the field of Medical Physics. 2017 / Aim The aim of this research was to contribute to clinical implementation of the small field dosimetry Code of Practice (CoP) that is due to be published by the International Atomic Energy Agency (IAEA) in collaboration with the American Association of Physicists in Medicine (AAPM) (1). A 6 cm × 6 cm virtual machine-specific reference (fmsr) field was established in a clinical 60Cobalt teletherapy beam used for conventional radiotherapy at Charlotte Maxeke Johannesburg Academic Hospital, and relative output factors were measured down to a set field size of 1 cm × 1 cm using three different models of Physikalisch-Technische Werkstatten (PTW) small field ionization chambers. Materials and Methodology The measurements were all performed on a Cobalt teletherapy unit (MDS Nordion Equinox, S/N 2009) in a PTW MP3 water phantom. The small field ionization chambers that were used were a PTW 31016 3D pinpoint 0.016 cm3, a PTW 31006 pinpoint 0.015 cm3 and a PTW 31010 semiflex 0.125 cm3. A calibrated PTW 30013 Farmer 0.6 cm3 ionization chamber was used to provide traceability for the cross calibration. A ―daisy chain‖ methodology was used to perform the cross calibration in a virtual fmsr field of 6 cm × 6 cm and then establish the absolute dose rate in a 4 cm × 4 cm field. Relative output factors as a function of field size were measured with each small field ionization chamber and then compared to published results. Results Small square fields from a 60Cobalt beam were created using the secondary collimators integrated into the unit. Equivalent square fields were calculated using the profiles obtained by the three ionization chambers during scanning and were in agreement with the ones that were programmed into the console. The coincidence of the central axis of the beam and the point of measurement for each detector was determined from the beam profiles. The cross calibration and daisy chain measurements resulted in a consistent dose rate of within + 0.6% in the 4 cm × 4 cm field when measured with the four different ionization chambers. For 6 cm × 6 cm, 4 cm × 4 cm, 3 cm × 3 cm and 2 cm × 2 cm field sizes, relative output factors obtained from the uncorrected detectors’ response agreed to within + 0.8 % between the three small field ionization chambers. The variation in the 1 cm × 1 cm field size was + 8.1 %. When compared to published data, large differences in field size correction factors were obtained. Conclusion Small field dosimetry in a 60Cobalt photon beam using three different PTW small field ionization chamber models was investigated. A cross calibration in a virtual msr field was done followed by a daisy chain process to determine the dose rate in a small field. Dose profiles and relative output factors were then measured and compared. The lack of lateral charge particle equilibrium and volume averaging effect was evident when using the PTW 31010 semiflex chamber in a 1 cm × 1 cm field. The PTW 31006 pinpoint and 31016 3D pinpoint were in close agreement for field sizes down to 1 cm × 1 cm with the 3D pinpoint performing as the best detector in this study. The optimal positioning of a detector should be determined from beam profile scans and not the engineering diagrams. The PTW 31016 3D pinpoint and PTW 31006 pinpoint are recommended for the determination of output factors in small field sizes. However, field output correction factors are required for both detectors in field sizes under 2 cm × 2 cm. Small field data published in the British Journal of Radiology (BJR) Supplement 25 (2) should not be used to benchmark dosimetry in modern 60Cobalt teletherapy units. / MT 2017

A dissertation submitted in accordance with the requirements for the degree of Master of Science in the Faculty of Science at theUniversity of Witwatersrand, Johannesburg, 2012. / AIM: This studied aimed at analysing the set-up error (margin) of head and neck cases, treated in a vacuum formed acrylic shell with an in-house immobilisation system. METHODS AND MATERIALS: Two population groups were studied, namely virtual simulated and intensity modulated radiotherapy (IMRT) cases. All cases were treated with the in-house immobilization system, which located centrally, but not longitudinally, to the treatment couch. Verification of the couch position, other than the isocentric angle, was not activated. The virtual simulated cases consisted of two lateral fields with a matched anterior neck field. The borders of these fields were chosen by the radiation oncologist. The IMRT cases were planned by a medical physicist and consisted of 6-9 fields of 3-4 intensity levels each. Digitally reconstructed radiographs (DRRs) of the 2 lateral fields and the anterior neck field for the virtual simulated cases, and the 2 lateral and anterior composite fields at the same isocentre for the IMRT cases, were printed and represented the ideal patient position. On the first day of treatment, megavoltage verification films were taken of the treated or positioning fields respectively. These verification films were compared to the DRRs and approved by a radiation oncologist. The absolute bed position in the vertical (Y), lateral (X) and longitudinal (Z) directions at the time of film approval, was used as the reference or ideal position. The absolute readings of the couch position that were captured daily over the course of treatment were then compared to the initial couch position to give an indication of the systematic and random errors. One linear accelerator was used in this study and weekly mechanical quality control (QC) was performed on it. RESULTS: The total number of daily fractions (F) studied in this thesis was 5644 and 600 for virtual simulated and IMRT cases respectively. The systematic error of this population was 4.7 and 4.4 mm for the virtual simulated and IMRT cases respectively. This compares well with published results using a similar immobilisation system. The random error of this population was 7 mm and 6.1 mm for the virtual simulated and IMRT cases respectively. This is three times larger than the results reported in the literature (using a similar immobilization device). CONCLUSION: Offline monitoring of couch position provides insight into setup margins and this can contribute to realistic institutional planning target volumes. Better results were obtained in the IMRT cases and this could be due to the requirement for weekly verification imaging. Lack of radiation therapist vigilance and insufficient training were most likely responsible for the individual cases with systematic variations of larger than 3 cm. The data confirm that the immobilisation system can be located to a fixed position on the tabletop; this will allow online verification of absolute bed position for treatment and further decrease the chance of incorrect setup.

Philosophiae Doctor - PhD / The study outlines five areas of intervention in the development of women studies and politics on the continent. Firstly, it examines the problematic construction and the inclusion of women in the narratives of the liberation struggle in South Africa. Secondly, the study identifies the sphere of intellectual debates as one of the crucial sites in the production of historical knowledge about the legacies of liberation struggles on the continent. Thirdly, it traces the intellectual trajectory of Charlotte Maxeke as an embodiment of the intellectual contributions of women in the struggle for liberation in South Africa. In this regard, the study traces Charlotte Maxeke as she deliberated and engaged on matters pertaining to the welfare of the Africans alongside the prominent intellectuals of the twentieth century. Fourthly, the study inaugurates a theoretical departure from the documentary trends that define contemporary studies on women and liberation movements on the continent. Fifthly, the study examines the incorporation of Maxeke's legacy of active intellectual engagement as an integral part of gender politics in the activities of the Women's Section of the African National Congress. In the areas identified, the study engages with the significance of the intellectual inputs of Charlotte Maxeke in South African history. / South Africa

<p>The study outlines five areas of intervention in the development of women&rsquo / s studies and politics on the continent. Firstly, it examines the problematic construction and the inclusion of women in the narratives of the liberation struggle in South Africa. Secondly, the study identifies the sphere of intellectual debates as one of the crucial sites in the production of historical knowledge about the legacies of liberation struggles on the continent. Thirdly, it traces the intellectual trajectory of Charlotte Maxeke as an embodiment of the intellectual contributions of women in the struggle for liberation in South Africa. In this regard, the study traces Charlotte Maxeke as she deliberated and engaged on matters pertaining to the welfare of the Africans alongside the prominent intellectuals of the twentieth century. Fourthly, the study inaugurates a theoretical departure from the documentary trends that define contemporary studies on women and liberation movements on the continent. Fifthly, the study examines the incorporation of Maxeke&rsquo / s legacy of active intellectual engagement as an integral part of gender politics in the activities of the Women&rsquo / s Section of the African National Congress. In the areas identified, the study engages with the significance of the intellectual inputs of Charlotte Maxeke in South African history.</p>

<p>The study outlines five areas of intervention in the development of women&rsquo / s studies and politics on the continent. Firstly, it examines the problematic construction and the inclusion of women in the narratives of the liberation struggle in South Africa. Secondly, the study identifies the sphere of intellectual debates as one of the crucial sites in the production of historical knowledge about the legacies of liberation struggles on the continent. Thirdly, it traces the intellectual trajectory of Charlotte Maxeke as an embodiment of the intellectual contributions of women in the struggle for liberation in South Africa. In this regard, the study traces Charlotte Maxeke as she deliberated and engaged on matters pertaining to the welfare of the Africans alongside the prominent intellectuals of the twentieth century. Fourthly, the study inaugurates a theoretical departure from the documentary trends that define contemporary studies on women and liberation movements on the continent. Fifthly, the study examines the incorporation of Maxeke&rsquo / s legacy of active intellectual engagement as an integral part of gender politics in the activities of the Women&rsquo / s Section of the African National Congress. In the areas identified, the study engages with the significance of the intellectual inputs of Charlotte Maxeke in South African history.</p>