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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Linear accelerator multileaf collimator quality control methodologies in radiotherapy

Rule, Ayron Edward 14 September 2016 (has links)
A Dissertation submitted to the faculty of science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. May 2016 / The multileaf collimator (MLC) system introduction into clinical linear accelerators (Linacs), facilitated computer-control and verification of complex treatment, and results in an increase in patient set up speed. An MLC system thus requires a re-evaluation of the quality assurance (QA) requirements for beam collimation. This study investigated, developed, performed and evaluated QA effors for conventional MLCs with the aim to evaluate the efficacy and reproducibility of the quality control (QC) procedures with different detectors. The performance of MLCs for an Elekta (Livingstone hospital) and siemens (Charlotte Maxeke Johannesburg academic hospital) linac were examined. The major QC procedures studied were leaf matching, leaf position accuracy, intraleaf leakage and transmission through abutting leaves. Three portal imaging devices (radiographic film, radiochromic film and an electronic portal imaging device) and a PTW LA48 linear array were used as detectors. Record and verify data management systems were used to set up and execute the procedures. The calibration of all the potal imaging devices was also performed. The calibration procedure of the portal imaging devices is linac specific in execution. The profiles obtained indicated consistency across device and time. A combined single execution procedure is viable and reproducible on all platforms. The results show tha the calibration of imaging devices is of great importance. The MLC design influences the range and extent of QC that can be performed. This may impact on the accuracy with advanced technologies requiring high conformity and reproducible leaf movement, can be deliverd. Imaging devices each have specific resource requirement issues affecting the efficacy of their use.
2

Mitochondrial dynamics in the radiation response of cancer cells

Parker, Michelle January 2017 (has links)
Mitochondria are involved in the regulation of key cellular processes that determine the response of cells to damage. Mitochondrial fission and fusion are associated with cell cycle regulation, apoptosis, cellular bioenergetics and redox status, which contribute to cellular homeostasis and damage response. The study aimed to describe and correlate cancer cell mitochondrial features and inherent radiosensitivity, and to determine the effect of modulation of mitochondrial dynamics on radiation response using a fission inhibitor, Mdivi-1. Methods: Mitochondrial status in a number of cancer cell lines was characterised by assessment of mitochondrial morphology, respiration and membrane potential using MitoTracker® Red staining, respirometry and JC-1 ratiometric staining, respectively. Correlations with radiation sensitivity were performed. Radiation- and Mdivi-1-induced changes in mitochondrial morphology were also examined. Responses to various schedules of radiation and Mdivi-1 treatment were assessed using clonogenic survival. Microscopy was used to quantify apoptosis, micronuclei and mitotic features, while cell cycle dynamics were analysed using flow cytometry. Results: Notably, modulation of mitochondrial fission using Mdivi-1 significantly increased radiation response in A549 cancer cells. Mdivi-1 reduced fragmentation, increased membrane potential and induced cytotoxicity, cytogenetic damage, apoptosis and G2/M cell cycle arrest. However, with the exception of survival, sub-additive responses were consistently observed when Mdivi-1 was combined with radiation. Sub-lethal damage repair was unaffected by Mdivi-1. Characterisation of cancer cell lines revealed inherent diversity in radiation response and mitochondrial morphology, membrane potential and respiration, and several correlations were identified. Discussion and conclusions: Inhibition of mitochondrial fission was shown for the first time to enhance radiosensitivity in cancer cells, and to induce cytotoxicity. Mitochondrial modulators may therefore have therapeutic application. However, the sub-additive responses observed with Mdivi-1-radiation interactions suggest that optimisation of treatment scheduling may be important. The Mdivi-1-induced mitotic arrest may, in part, be responsible for the observed radiosensitisation, as cells accumulate in a radiosensitive cell cycle phase. In addition, the finding that Mdivi-1 treatment induced micronuclei suggested that the radiosensitisation may result from the interaction of cytogenetic damage induced by each agent. Overall, mitochondrial dynamics appears to significantly influence radiation response.
3

Optimal radiotherapy planning using digital computers

Cooper, Richard Edward Mounteney January 1969 (has links)
190 leaves : ill. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Computing Sciences, 1971
4

Optimal radiotherapy planning using digital computers.

Cooper, Richard Edward Mounteney. January 1969 (has links) (PDF)
Thesis (Ph.D.) -- University of Adelaide, Dept. of Computing Sciences, 1971.
5

A needs assessment approach to program development in radiotherapy

Wenzel, Lari B. January 1980 (has links)
Thesis (M.S.)--University of Wisconsin--Madison, 1980. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 49-52).
6

Video-based patient positioning for external beam radiation therapy /

Hadley, Scott W. January 2002 (has links)
Thesis (Ph. D.)--University of Chicago, Dept. of Radiation and cellular oncology, 2002. / Includes bibliographical references. Also available on the Internet.
7

A probabilistic approach to incorporating localization uncertainty into external beam radiotherapy treatment design /

Fontenla, Ernesto Daniel. January 1999 (has links)
Thesis (Ph. D.)--University of Chicago, Dept. of Radiology, June 1999. / Includes bibliographical references. Also available on the Internet.
8

Dose calculations relating to the use of negative pi-mesons for radiotherapy

Henry, Marguerite Irene January 1973 (has links)
Physical (or absorbed) dose distributions and biologically effective distributions are calculated in this thesis for (a) monoenergetic beams (b) "shaped" continuous energy spectra of negative pi-mesons. The results of these calculations confirm qualitatively the claims made for the advantages of negative pi-mesons for radiotherapy and give some quantitative measures of these advantages. The first and most detailed calculations include only dose contributions from primary pions and from the charged particles released in the nuclear disintegrations which occur at the end of the negative pion tracks. The physical dose calculations are based on published data on the number and energy of the charged particles from these disintegrations and on published range-energy-stopping power data for the primary pions and for the charged disintegration products. Two physical dose calculations are made, assuming (a) 29.0 MeV and (b) 35.6 MeV total kinetic energy per pion capture of the charged particles from the "stars". These calculations show that, for a monoenergetic beam having a 20 cm range, the dose at the Bragg peak is 10 to 12 times the entrance dose. Biologically effective dose distributions are calculated, both for aerobic and for anoxic conditions, using available (but uncertain) data for the dependence of (a) "relative biological effectiveness" (RBE) and (b) "oxygen enhancement ratio" (OER) on the stopping power of the medium. All calculations are repeated for two different assumptions with respect to dependence of "RBE" on stopping power. On the assumptions made, for a monoenergetic beam in the Bragg peak the effective RBE and the effective OER are approximately 1.9 and 1.65, respectively, for the lower RBE values used and about 2.5 and 1.55, respectively, for the higher RBE values. The calculations for continuous energy spectra of negative pions demonstrate the possibility of selecting a "shaped" spectrum which gives an essentially constant dose through a specified depth with a surface dose which is only 25 to 30% of this constant dose. For a spectrum chosen to give constant biologically effective dose from 12 to 20 cm depth, assuming the lower RBE values (referred to above), the effective RBE increases from about 1.35 at 12 cm to I.65 at 20 cm and the effective OER decreases from about 2.00 to 1.75 over the same depth interval. Assuming the higher RBE values, the corresponding range of effective RBE values is from 1.6 to 2.1 and the range of effective OER values I.85 to 1.65. An attempt is made to estimate corrections for the effects which were neglected in the detailed calculations, namely, (a) muon and electron contamination of the incident pion beam, (b) loss of pions from the beam by interactions with nuclei of the medium before coming to rest and (c) dose contributions from neutrons released in the "stars" at the end of the pion tracks. When these corrections are made, it is shown for a monoenergetic beam of 20 cm range that the ratio of the maximum dose in the Bragg peak to the surface dose is about 6.5 in good agreement with published experimental results. Also, it is shown that, when all corrections are taken into account, for a "shaped" spectrum which delivers a constant physical dose from 12 to 20 cm depth, about 30% of the total energy absorbed in the patient is absorbed within the constant dose region. Calculated values of RBE and OER are compared with published experimental values but the validity of the comparison is very questionable. / Science, Faculty of / Physics and Astronomy, Department of / Graduate
9

Intra-institutional end to end testing accuracy of modern technologies and techniques in radiotherapy

Ramaloko, Thuso MacDonald January 2017 (has links)
A dissertation submitted in partial fulfillment of the requirements for the degree Master of Science, Department of Medical Physics, school of Physics. Johannesburg 2017 / Objective: Intensity Modulated Radiation Therapy (IMRT) treatment techniques have evolved and the current level of interest in IMRT warrants a determination of the accuracy in delivering IMRT, in multiple institutions practicing IMRT. The aim of this study was to (a) perform inphantom end to end testing accuracy of 3D-Conformal Radiation Therapy (CRT) and different IMRT techniques, (b) check the dosimetric impact of dose delivered with deliberate offsets in the physical positioning of the phantoms using Cone-Beam Computed tomography (CBCT) and (c) use CBCT based IGRT to establish the extrinsic setup errors achieved between set-up and delivery of the planned dose on phantoms. Materials and Method: Studies were conducted in 3 institutions. An anthropomorphic phantom and a MatriXXEvolution with MULTICube were CTscanned and the CT slices were transferred to the treatment planning systems (TPSs). The transfered CT-slices were used to create a patient model and plans were created on hypothetical targets situated adjacent to an organ at risk (OAR). A virtual water phantom was also created in the same TPS and the same plans were created for verification purposes. The plans were transferred to a linear accelerator using a record and verify network system. The phantoms were positioned on the treatment couch and the dose delivered according to the treatment planning protocol. Statistical tools were used to analyse the delivered dose to the planed dose. Results and discussion: The end to end testing per institution was found to be less than 5% for dynamic IMRT and 2% for 3D-CRT when comparing planned to the measured dose. Comparison between institutions resulted in less than 7% dose difference for dynamic IMRT and 2% difference for 3D-CRT. Phantom setup errors were found to be less than 6 mm, 4 mm and 3 mm for the pretreatment, post-correction and post-delivery setups respectively. The dose difference delivered with a deliberate 3mm setup error was found to be less than 1%, 3% and 4% for the Catphan®, Pelvis and Head and Neck plans respectively. Conclusion: The overall accuracy of the treatment techniques at each institution was determined successfully. Independent phantom setups are likely to indicate the best possible setup precision as they are much easier to setup reproducibly than a patient with an internal margin for involuntary movement. Pre-treatment imaging was able to detect setup errors of 6 mm in Pelvis cases. Head and neck treatments delivered with advanced techniques are the most sensitive dosimetrically to small setup errors. / XL2018
10

A model for the physical optimization of external beam radiotherapy

Holmes, Timothy William. January 1900 (has links)
Thesis (Ph.D.)--University of Wisconsin--Madison, 1993. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 199-207).

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