Thesis (M.S.)--Oregon State University, 2011. / Printout. Includes bibliographical references (leaves 56-58). Also available on the World Wide Web.

Thesis (M. Sc.)--University of Canterbury, 2006. / Typescript (photocopy). "August 2006." Includes bibliographical references (leaves 105-108). Also available via the World Wide Web.

Analytical and numerical models for reconstructing clinical bremsstrahlung spectra with maximum photon energies in the range 4 to 30 MeV from indirect measurements such as transmission or depth-dose curves are investigated and compared. The iterative and Laplace transform models of Huang et al and Archer and Wagner are extended to the energy region of interest and a further two models based on thin and thick target bremsstrahlung theory developed. Calculated transmission curves for a set of 21 simulated and measured bremsstrahlung spectra covering a broad range of filtration conditions are used to assess each model's ability to represent photon spectra. A model based on the Schiff expression for forward-directed thin-target bremsstrahlung differential in photon energy with added inherent filtration is shown to provide a promising method for reliably reconstructing megavoltage spectra in terms of 3 parameters. For this model, input data was reproduced to within 0.1 percent, this being the same order of magnitude as the accuracy of its generation and within expected uncertainties for measured input data. Inclusion of a fourth parameter in the model is shown to allow the effective maximum photon energy present in the spectrum to be derived. The considerations involved in the practical use of reconstruction models to derive clinical photon spectra from measured transmission and depth-dose data and likely applications of these spectra are discussed.

The work reported in this thesis investigates the possible use of thin film teflon electrets as X-ray dosimeters. Electrets were prepared by corona- and breakdown field-charging and found to exhibit a number of properties that would render them suitable for personnel dosimetry. The stability of the residual electret charge as a function of environment was also studied and it was found that hot, humid or unshielded conditions led to rapid charge decay. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, February 2017 / There has been increasing public concern regarding adverse health effects due to power frequency electric and magnetic fields. Safety guidelines/standards for electric and magnetic field exposures have been established by different public organizations. However, the link between low frequency (power frequency) electric and magnetic field exposure and adverse health effects is not yet well established. Limits on human exposure to low frequency electric and magnetic fields are fundamentally specified for in-situ fields in tissues/organs. These dosimetric limits are referred to as Basic Restrictions for protection against potentially adverse effects from electro-stimulation. In addition, secondary limits, the exposure Reference Levels in environmental electric and magnetic fields are also given for practical compliance purposes. These are generally derived from the Basic Restrictions based on uniform-fields with a provision that the Basic Restrictions must be observed for non-uniform cases. In practice, any structure influences the electric fields in High Voltage systems, and thus creates electric field non-uniformity. The human exposure of the general public to electric fields from Eskom’s 765 kV transmission network operating at 50 Hz, is addressed through physical measurements, theoretical predictions and 3-D human model dosimetry, which is presented in this dissertation. / MT 2017

Intracavitary high-dose-rate brachytherapy (HDRBT) is a treatment option for endometrial cancer, depending on the cancer stage. Because of the steep high dose gradient of HDRBT, very small differences in the treatment plans, surrounding organ’s anatomy, or procedures during the treatment could potentially cause significant dose variation to the tumor, as well as organs at risks (OAR) nearby the treatment area, which could result in unwanted radiobiological side effects. In this retrospective study, the radiobiological plan evaluation parameters Equivalent Uniform Dose (EUD), Normal Tissue Complication Probability (NTCP) are used as assessment tools to evaluate HDRBT plans. Furthermore, gynecological applicator position in the coordinate system, and possible dose variations to the tumor and critical organs from the initial fraction in comparison with subsequent fractions over the entire multi fractionated treatment are studied. The evaluations were performed for 118 HDR treatment plans for 30 patients by registration of the subsequent treatment plans into the initial CT-image guided plan. Dose fractionation regimens varied from 4Gy to 7Gy per fraction, 1 or 2 fractions per week, depending on the cancer stage. Our results demonstrate no significant radiobiological impacts on organs at risks (OAR). In addition, the results of the applicator positions’ study indicate that improvement of immobilization and localization devices are recommended. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Six radiation dosimetry and medical physics problems were analyzed using a beta version of MCNP 5 as part of an international intercomparison of radiation dosimetry computer codes, sponsored by the European Commission committee on the quality assurance of computational tools in radiation dosimetry. Results have been submitted to the committee, which will perform the inter-code comparison and publish the results independently. A comparison of the beta version of MCNP 5 with MCNP 4C2 is made, as well as a comparison of the new Doppler broadening feature. Comparisons are also made between the *F8 and F6 tallies, neutron tally results with and without the use of the S(a,b) cross sections, and analytically derived peak positions with pulse height distributions of a Ge detector obtained using the beta version of MCNP 5. The following problems from the study were examined: Problem 1 was modeled to determine the near-field angular anisotropy and dose distribution from a high dose rate 192Ir brachytherapy source in a surrounding spherical water phantom. Problem 2 was modeled to find radial and axial dose in an artery wall from an intravascular brachytherapy 32P source. Problem 4 was modeled to investigate the response of a four-element TLD-albedo personal dosimeter from neutrons and/or photons. Significant differences in neutron response with S(a,b) cross sections compared to results without these cross sections were found. Problem 5 was modeled to obtain air kerma backscatter profiles for 150 and 200 kVp X-rays upon a water phantom. Air kerma backscatter profiles were determined along the apothem and diagonal of the front face of the phantom. A comparison of experimental results is also made. Problem 6 was modeled to determine indirect spectral and energy fluences upon two neutron detectors within a calibration bunker. The largest indirect contribution was found to come from low energy neutrons with an average angle of 47o where 0o is a plane parallel to the floor. Problem 7 was modeled to obtain pulse height distributions for a germanium detector. Comparison of analytically derived peaks with peak positions in the spectra are made. An examination of the Doppler broadening feature is also included.

Thesis (M.S.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (p. 57-63).

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