published_or_final_version / Medicine / Master / Doctor of Medicine

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The thesis presents a comparison of four techniques used for stereotactic radiosurgery, consisting of the static conformal beam, static cone-based, proton therapy, and the Gamma Knife techniques. The comparisons involved six test cases in which phantom target lesions were created in the center of the modified anthropomorphic RandoRTM head. The phantom lesions presented in the study were extreme irregular cases that ranged in shape and volume and were near a critical structure to receive minimal dose during treatment planning. The best treatment plans from each technique for all studies were selected and the extracted data was analyzed using physical and biological parameters. Correlations between integral biological effective dose (normal brain) and normal tissue complication probability were analyzed as a function of dose conformity (PITV), and correlations between tumor control probability and integral biological effective dose (tumor) as a function of dose homogeneity (MDPD) were analyzed, as well. These parameter pairings showed strong links. The static conformal beam and the proton SOBP techniques consistently provided low PITV and MDPD values for all cases, including the most irregular and complicated cases. Higher PITV and MDPD values, typically associated with static cone-based and the Gamma Knife techniques, were due to normal tissue and tumor tissue, respectively, being irradiated at higher dose levels than the prescribed dose. For these cases, as the PITV increased, the NTCP increased, as well, due to high doses created within the normal tissue found within the prescription isodose surface.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 5 uppsatser.

Thesis (M.Sc.). / Written for the Medical Physics Department. Title from title page of PDF (viewed 2008/12/09). Includes bibliographical references.

Thesis (M.S.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Originally presented as the author's Thesis (Ph. D.)--"Otto von Guericke" Universität Magdeburg, 2003. / "Elektrotechnik"--Cover. Includes bibliographical references (p. 145-149).

Radiotherapy can be highlighted as one possible treatment of cancer. From this point of view, the planning system for radiotherapic treatment is crucial. In order to check the software for the computerized planning of the Cobalt-60 equipment, a series of tests was defined following the standards given by the: TEC DOC 1151 protocol " Aspectos Físicos da Garantia de Qualidade em Radioterapia, Protocolo de Controle de Qualidade (TEC DOC 1151, 2000), o Technical Reports Series Number 430 (TRS 430) (IAEA, 2004), o TRS 398 Absorbed Dose Determination in External Beam Radiotherapy: An International Code of Practice for Dosimetry based on Standards of Absorbed Dose to Water (TRS 398, 2004). The depth dose of interest of the acrylic simulators used to control the quality of computerized tomography were evaluated, tests of the software and hardware as well as the input and output of data were analyzed, tests of the boundary conditions, of the percetual dose and of the field profile were also performed. An analysis of the results show that the performance of the software results was satisfactory. The only deviattions appeared in the field profile tests that do not fulfilled the expectations due to the limitations of the system. / A radioterapia pode ser destacada como uma possibilidade de tratamento de câncer. Partindo deste propósito, o sistema de planejamento para o tratamento radioterápico é muito importante. Com a finalidade de averiguar o software de planejamento computadorizado do equipamento de Cobalto-60, definiu-se um conjunto de testes retirados dos protocolos TEC DOC 1151 Aspectos Físicos da Garantia de Qualidade em Radioterapia, Protocolo de Controle de Qualidade (TEC DOC 1151, 2000), o Technical Reports Series Number 430 (TRS 430) (IAEA, 2004), o TRS 398 Absorbed Dose Determination in External Beam Radiotherapy: An International Code of Practice for Dosimetry based on Standards of Absorbed Dose to Water (TRS 398, 2004). Avaliamos a dose na profundidade de interesse dos simuladores de acrílico utilizados para controle de qualidade em tomografia computadorizada, realizamos testes de software e hardware bem como a entrada e saída de dados, testes de contorno, percentual de dose profunda e perfil de campo. Verificou-se que os resultados foram satisfatórios, apenas o teste de perfil de campo não satisfez as expectativas devido a limitações no sistema.

O controle de qualidade do feixe é fundamental para garantir os requisitos mínimos de operação aos serviços de radioterapia, visto que a avaliação de parâmetros como simetria, planura, penumbra, fatores filtro e bandeja além de outros parâmetros dosimétricos é imprescindível para garantir constância aos tratamentos radioterápicos minimizando erros na entrega da dose. A avaliação destes parâmetros em radioterapia normalmente é realizada através de câmaras de ionização, filmes radiográficos ou detectores semicondutores sendo eles diodos e MOSFETs. Nos últimos anos o crescimento da utilização da dosimetria opticamente estimulada (OSL) na dosimetria individual externa em diversos países da Europa, USA e America latina como México e Peru proporcionou a aplicação de detectores OSL também na dosimetria em radioterapia visando à avaliação de parâmetros de feixe. A técnica de OSL une características técnicas encontradas em filmes e TLD, acrescidas de novas propriedades não possíveis nas tecnologias utilizadas anteriormente, por exemplo: possibilidade de re-leitura do dosímetro, integração de dose com avaliação de doses intermediárias entre exposições no mesmo dosímetro e simplicidade no processo de leitura. Recentemente a Landauer Inc lançou no mercado americano fitas dosimétricas de OSL para a análise do perfil de dose em Tomografia Computadorizada (TC). Neste trabalho foi avaliada a utilização deste detector OSL em forma de fita, na determinação de parâmetros de qualidade em radioterapia tais como simetria e planura, fatores filtro e bandeja, porcentagem e dose profunda (PDP) e penumbra. Os resultados obtidos permitem concluir que o detector estudado se apresenta eficaz na determinação dos parâmetros de qualidade, porém a metodologia de análise de dados bem como o setup utilizado na irradiação inicial devem ser reformulados buscando obter resultados mais precisos de forma a validar a utilização deste método na rotina de trabalho em radioterapia. / Beam´s quality control is fundamental to ensure minimum operation requirements to radiotherapy services, since parameters evaluation, such as symmetry, planura, shade, filter factors and tray, amongst other ones, is necessary to guarantee stability to radiotherapy treatments, which minimize errors at dose delivery. The evaluation of those parameters in radiotherapy is normally executed through ionization compartments, radiographic films or semiconductor detectors, specifically diode and MOSFETs. Through the last years, the utilization of optically stimulated dosimetry at external individual dosimetry increased in several Europe countries, USA and Latin America countries, such as Mexico and Peru, which made it possible to apply OSL detectors at dosimetry to radiotherapy as well, in order to evaluate clusters parameters of quality. The OSL technique incorporate technical characteristics, found in films and TLD, to new proprieties, which were not available at preceding technologies, such as: possibility of dosimetry rereading, dose integration with intermediary doses evaluation between exposure at the same dosimeter and simplicity at the reading process. Recently, Launder Inc launched in the American market OSL dosimetric ribbons to dose profile analysis in computed tomography (TC). In this paper, it was analyzed this OSL tape shaped detector utilization, in order to determine parameters of quality in radiotherapy, such as symmetry and beam flatness, filter factors and tray, depth dose percentage and dose and shade. The results allowed to conclude that the studied detector is effective to determine parameters of quality. However, analysis methodology, as well as the used setup at initial irradiation, must be reformulated in order to get more accurate results, which it will allow to validate this method utilization at daily work routine in radiotherapy.

Abstract The use of image-guidance in surgery and radiotherapy has significantly improved patient outcome in neurosurgery and radiotherapy treatments. This work developed volume definition and verification techniques for image-guided applications, using a number of algorithms ranging from image processing to visualization. Stereoscopic visualization, volumetric tumor model overlaid on an ultrasound image, and visualization of the treatment geometry were experimented with on a neurosurgical workstation. Visualization and volume definition tools were developed for radiotherapy treatment planning system. The magnetic resonance inhomogeneity correction developed in this work, possibly the first published data-driven method with wide applicability, automatically mitigates the RF field inhomogeneity artefact present in magnetic resonance images. Correcting the RF inhomogeneity improves the accuracy of the generated volumetric models. Various techniques to improve region growing are also presented. The simplex search method and combinatory similarity terms were used to improve the similarity function with a low additional computational cost and high yield in region correctness. Moreover, the effects of different priority queue implementations were studied. A fast algorithm for calculating high-quality digitally reconstructed radiographs has been developed and shown to better meet typical radiotherapy needs than the two alternative algorithms. A novel visualization method, beam's light view, is presented. It uses texture mapping for projecting the fluence of a radiation field on an arbitrary surface. This work suggests several improved algorithms for image processing, segmentation, and visualization used in image-guided treatment systems. The presented algorithms increase the accuracy of image-guidance, which can further improve the applicability and efficiency of image-guided treatments.