by Chan Pui-King. / Bibliography: leaf 45 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1984

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 132-138). Available also in a digital version from Dissertation Abstracts.

The characterization and measurement of the spatial, temporal and energy emission of air-scattered photons, electrons and neutrons generated near 10 MV or greater accelerator-based bremsstrahlung photon sources is becoming important in many applications. The national and homeland security research community is interested in developing technologies which can detect illicit materials at substantial standoff distances in outdoor environments. These systems are referred to as "active" interrogation systems and are defined as inspection systems that take advantage of an externally applied "source" to perform traditional imaging of, or to stimulate characteristic emissions from, an inspected object. A key concern in the development of these systems is the ability to effectively predict the dose equivalents at long standoff distances from these sources in order to ascertain the operational radiation safety of said systems. Current computational radiation transport simulation tools have the ability to effectively model these systems; however, a paucity of experimental data exists in comparing the results of these simulations. A methodology to assess the radiation dose surrounding a high-energy bremsstrahlung-based accelerator system for national defense applications was developed. Fluence-to-dose conversion coefficients for the International Commission on Radiation Units and Measurements operational quantity ambient dose equivalent were calculated for photons and electrons up to 25 MeV utilizing the Los Alamos National Laboratory Monte Carlo N-Particle code, MCNP5 Version 1.51. Special consideration was given to the treatment of secondary charged particle equilibrium in all simulations. An extensive set of system simulations was performed to model a prototype high-energy bremsstrahlung-based accelerator system to obtain photon, electron and neutron fluence spectra. These fluence data were folded with the calculated ambient dose equivalent conversion coefficients as well as previously published effective dose conversion coefficients. A set of integral air-scatter measurements for accelerator-generated primary and secondary radiations (photon and neutron) were performed around the prototype system in order to provide a comparative data set from which to determine the total dose equivalent both in the beam (on-axis) and outside of the beam (off-axis).

More than hundred years after the discovery of X-rays different kinds of ionizing radiation are ubiquitous in medicine, applied to clinical diagnostics and cancer treatment as well. Irrespective of their nature, the widespread application of radiation implies its precise dosimetric characterization and detailed knowledge of the radiobiological effects induced in cancerous and normal tissue. Starting with in vitro cell irradiation experiments, which define basic parameters for the subsequent tissue and animal studies, the whole multi-stage process is completed by clinical trials that translate the results of fundamental research into clinical application. In this context, the present dissertation focuses on the establishment of radiobiological in vitro cell experiments at unconventional, but clinical relevant radiation qualities. In the first part of the present work the energy dependent biological effectiveness of photons was studied examining low-energy X-rays (≤ 50 keV), as used for mammography, and high-energy photons (≥ 20 MeV) as proposed for future radiotherapy. Cell irradiation experiments have been performed at conventional X-ray tubes providing low-energy photons and 200 kV reference radiation as well. In parallel, unconventional quasi-monochromatic channeling X-rays and high-energy bremsstrahlung available at the radiation source ELBE of the Forschungszentrum Dresden-Rossendorf were considered for radiobiological experimentation. For their precise dosimetric characterization dosimeters based on the thermally stimulated emission of exoelectrons and on radiochromic films were evaluated, whereas just the latter was found to be suitable for the determination of absolute doses and spatial dose distributions at cell position. Standard ionization chambers were deployed for the online control of cell irradiation experiments. Radiobiological effects were analyzed in human mammary epithelial cells on different subcellular levels revealing an increasing amount of damage for decreasing photon energy. For this reason, the assumed photon energy dependence was reconfirmed for a cell line other than human lymphocytes, an important finding that was discussed on the 2007 Retreat of the German Commission on Radiological Protection. After successful finalization of the photon experiments the focus of the present dissertation was directed to the realization of in vitro cell irradiation experiments with laser-accelerated electrons. This research was carried out in the frame of the project onCOOPtics that aims on the development of laser-based particle accelerators, which promise accelerators of potentially compact size and more cost-effectiveness suitable for a widespread medical application, especially for high precision hadron therapy. The unique properties, i.e., the ultrashort bunch length and resultant ultrahigh pulse dose rate, of these unconventional particle accelerators demand for extensive investigations with respect to potential effects on the dosimetric and radiobiological characterization. Based on the experiences gained at ELBE first experiments on the radiobiological characterization of laser-accelerated electrons have been performed at the Jena Titanium:Sapphire laser system. After beam optimization, a sophisticated dosimetry system was established that allow for the online control of the beam parameters and for the controlled delivery of dose to the cell sample. Finally, worldwide first systematic in vitro cell irradiation experiments were carried out resulting in a reduced biological effectiveness for laser-accelerated electrons relative to the 200 kV X-ray reference, irrespectively on the biological effect and cell lines examined. These successful results are the basis for future in vivo studies and experiments with laser-accelerated protons.

Made available in DSpace on 2014-10-09T12:52:16Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:37Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:52:16Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:37Z (GMT). No. of bitstreams: 0 / Os Ensaios Não Destrutivos (END), são aplicados em testes de qualidade de componentes e de máquinas. Estes elementos não teriam um bom desempenho se fossem concebidos alheios à qualidade do projeto, aos materiais envolvidos, aos processos de fabricação e à metodologia de inspeção e manutenção. Um alto nível de tecnologia é aplicado com um objetivo específico, ou seja, à garantia da qualidade dos componentes e do bom funcionamento dessas máquinas, seja na indústria e na geração e conversão de energia, incluindo a nuclear. A globalização nos diversos ramos da indústria leva a um aumento na quantidade de projetos e produtos contextualmente multinacionais. Surgem, as seguintes questões: como assegurar que os componentes e os processos utilizados se disponhem de alto índice na qualidade? Como otimizar os métodos e os rocessos de teste de materiais para assegurar a isenção de defeitos que possam afetar o esempenho dos componentes? As respostas para as questões se encontram notadamente na aplicação dos END. A análise de materiais complexos (não homogêneos) por meio de END requer um estudo detalhado dos sinais de resposta dos sensores. Um sistema de medidas e controle de processos não destrutivos usando radiação gama ou beta, em função do material a ser analisado foi desenvolvido. Esse sistema envolve: (a) Interface de entrada/saída (Hardware) e (b) Interface gráfica (Software). Na análise não destrutiva faz-se a comparação do sinal proveniente do sensor com um sinal preestabelecido (Set Point) ou sinal de referência, o qual é ajustado na Interface de entrada/saída. Após o processamento geral, o sistema tomará a decisão de rejeitar ou não o material analisado. A Interface de entrada/saída é implementada por um equipamento eletrônico constituído pelo MCS51, com a finalidade de fornecer um meio físico para troca de nformações, via de comunicação serial RS232, entre o sensor e o microcomputador . A Interface gráfica (programa computacional) foi escrita em linguagem C++ visual. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The purpose of this study was to evaluate the effectiveness of the database system used at the South African Radiation Control Authority and compare it with RAIS (Regulatory Authority Information System). A radiation regulatory authority requires an adequate and effective data management system in order to carry out its regulatory control program efficiently and effectively. RAIS is a comprehensive system that includes all of the main functionality required to support a regulatory framework. A mixed methods approach, including a quantitative descriptive comparative evaluation research study was conducted to determine if the database system currently used by the South African Radiation Control Authority is effective as a data management tool for a regulatory body. Two analyses were conducted. Firstly, the specification records of the South African database system were compared with that of RAIS. Secondly, current database users were surveyed by means of a structured questionnaire. Both analyses reveal that RAIS performs better than the Radiation Control database in the main areas of the regulatory framework. The study results also highlight some of the shortcomings and strengths of the Radiation Control database / Medical Informatics / M.A. (Public Health)

The purpose of this study was to evaluate the effectiveness of the database system used at the South African Radiation Control Authority and compare it with RAIS (Regulatory Authority Information System). A radiation regulatory authority requires an adequate and effective data management system in order to carry out its regulatory control program efficiently and effectively. RAIS is a comprehensive system that includes all of the main functionality required to support a regulatory framework. A mixed methods approach, including a quantitative descriptive comparative evaluation research study was conducted to determine if the database system currently used by the South African Radiation Control Authority is effective as a data management tool for a regulatory body. Two analyses were conducted. Firstly, the specification records of the South African database system were compared with that of RAIS. Secondly, current database users were surveyed by means of a structured questionnaire. Both analyses reveal that RAIS performs better than the Radiation Control database in the main areas of the regulatory framework. The study results also highlight some of the shortcomings and strengths of the Radiation Control database / Medical Informatics / M.A. (Public Health)

No description available.

As lesões dermatológicas submetidas à terapia com fontes de radiação podem apresentar diferentes padrões de malignidade. Os tumores de pele mais comumente encontrados nos serviços de radioterapia são os carcinomas. A radioterapia de lesões dermatológicas é realizada com feixes de radiação de baixa penetração como os raios-X de ortovoltagem, feixes de elétrons e fontes radioativas (192Ir, 198Au, e 90Sr) arranjadas em moldes superficiais ou aplicadores metálicos. O presente trabalho teve como objetivo analisar o perfil de distribuição de dose terapêutica produzida por fontes de radiação utilizadas em procedimentos radioterápicos em lesões superficiais da pele. As medidas experimentais, para as análises dosimétricas das fontes de radiação, foram comparadas com cálculos obtidos no sistema computacional baseado no Método de Monte Carlo. Os resultados obtidos com os cálculos computacionais através do código MCNP-4C apresentaram uma boa concordância com as medidas experimentais. As comparações das medidas experimentais com os cálculos obtidos através do código MCNP-4C, foram utilizadas para validar os cálculos e assim possibilitar o uso de dados de simulação para aplicação em casos clínicos de rotina. A comparação entre diferentes modalidades podem fornecer um indicativo dos procedimentos mais adequados em cada caso clínico. / Skin lesions undergoing therapy with radiation sources may have different patterns of malignancy. Malignant lesions or cancer most commonly found in radiotherapy services are carcinomas. Radiation therapy in skin lesions is performed with low penetration beams and orthovoltage X-rays, electron beams and radioactive sources (192Ir, 198Au, e 90Sr) arranged on a surface mold or in metal applicator. This study aims to analyze the therapeutic radiation dose profile produced by radiation sources used in skin lesions radiotherapy procedures . Experimental measurements for the analysis of dosimetric radiation sources were compared with calculations obtained from a computer system based on the Monte Carlo Method. Computational results had a good agreement with the experimental measurements. Experimental measurements and computational results by the MCNP4C code were both physically consitent as expected. These experimental measurements compared with calculations using the MCNP-4C code have been used to validate the calculations obtained by MCNP code and to provide a reliable medical application for each clinical case.