Thesis (doctoral)--University of Göteborg, 1998. / Added t.p. with thesis statement inserted.

Thesis (M.S.)--University of Michigan, 2007. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 90-93).

Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 191-200).

Thesis (Ph.D.) - Carleton University, 2007. / Includes bibliographical references (p. 154-171). Also available in electronic format on the Internet.

Thesis (M. Sc.)--Carleton University, 2001. / Includes bibliographical references (p. 86-96). Also available in electronic format on the Internet.

<p>Patients undergoing cardiac catheterization are potentially at risk of radiation-induced health effects from the interventional fluoroscopic X-ray imaging used throughout the clinical procedure. The amount of radiation exposure is highly dependent on the complexity of the procedure and the level of optimization in imaging parameters applied by the clinician. For cardiac catheterization, patient radiation dosimetry, for key organs as well as whole-body effective, is challenging due to the lack of fixed imaging protocols, unlike other common X-ray based imaging modalities. </p><p>Pediatric patients are at a greater risk compared to adults due to their greater cellular radio-sensitivities as well as longer remaining life-expectancy following the radiation exposure. In terms of radiation dosimetry, they are often more challenging due to greater variation in body size, which often triggers a wider range of imaging parameters in modern imaging systems with automatic dose rate modulation. </p><p>The overall objective of this dissertation was to develop a comprehensive method of radiation dose estimation for pediatric patients undergoing cardiac catheterization. In this dissertation, the research is divided into two main parts: the Physics Component and the Clinical Component. A proof-of-principle study focused on two patient age groups (Newborn and Five-year-old), one popular biplane imaging system, and the clinical practice of two pediatric cardiologists at one large academic medical center. </p><p>The Physics Component includes experiments relevant to the physical measurement of patient organ dose using high-sensitivity MOSFET dosimeters placed in anthropomorphic pediatric phantoms. </p><p>First, the three-dimensional angular dependence of MOSFET detectors in scatter medium under fluoroscopic irradiation was characterized. A custom-made spherical scatter phantom was used to measure response variations in three-dimensional angular orientations. The results were to be used as angular dependence correction factors for the MOSFET organ dose measurements in the following studies. Minor angular dependence (< ±20% at all angles tested, < ±10% at clinically relevant angles in cardiac catheterization) was observed.</p><p>Second, the cardiac dose for common fluoroscopic imaging techniques for pediatric patients in the two age groups was measured. Imaging technique settings with variations of individual key imaging parameters were tested to observe the quantitative effect of imaging optimization or lack thereof. Along with each measurement, the two standard system output indices, the Air Kerma (AK) and Dose-Area Product (DAP), were also recorded and compared to the measured cardiac and skin doses – the lack of correlation between the indices and the organ doses shed light to the substantial limitation of the indices in representing patient radiation dose, at least within the scope of this dissertation.</p><p>Third, the effective dose (ED) for Posterior-Anterior and Lateral fluoroscopic imaging techniques for pediatric patients in the two age groups was determined. In addition, the dosimetric effect of removing the anti-scatter grid was studied, for which a factor-of-two ED rate reduction was observed for the imaging techniques. </p><p>The Clinical Component involved analytical research to develop a validated retrospective cardiac dose reconstruction formulation and to propose the new Optimization Index which evaluates the level of optimization of the clinician’s imaging usage during a procedure; and small sample group of actual procedures were used to demonstrate applicability of these formulations.</p><p>In its entirety, the research represents a first-of-its-kind comprehensive approach in radiation dosimetry for pediatric cardiac catheterization; and separately, it is also modular enough that each individual section can serve as study templates for small-scale dosimetric studies of similar purposes. The data collected and algorithmic formulations developed can be of use in areas of personalized patient dosimetry, clinician training, image quality studies and radiation-associated health effect research.</p> / Dissertation

O presente trabalho mostra as diferenças de dose encontradas em meios de diferentes densidades eletrônicas, simulando tecido adiposo, muscular, ósseo e cavidade aérea, comparando medidas experimentais com feixe de fótons de 6 MeV e valores resultantes de algoritmos de cálculo existentes em um sistema de planejamento radioterápico. Para isso foram utilizados dosímetros termoluminescentes posicionados acima, dentro e abaixo de cada objeto simulador e medidos os perfis de dose ao longo do eixo longitudinal e do eixo transversal. As simulações computacionais foram realizadas com dois algoritmos de cálculo presentes na versão 8.5 do sistema de planejamento Eclipse: o Pencil Beam Convolution e o Analytical Anisotropic Algorithm. Comparando doses em um mesmo ponto, com e sem heterogeneidades, foram encontradas diferenças percentuais de até 12%, quando os algoritmos de correção de heterogeneidades não foram aplicados. Analisando essas comparações, pode-se observar também qual dos algoritmos de cálculo mais se aproxima dos valores experimentais, propondo ser o algoritmo de maior confiabilidade. / This work presents the dose variations obtained when phantoms of different electronic densities were used, simulating fat tissue, muscle, bones and air cavities, comparing experimental data with a 6 MeV photon beams and the values calculated by the treatment planning system algorithms. Thermoluminescent dosimeters were positioned above, inside and below each phantom measuring the dose along the depth and along a profile. The computational simulation was done by two algorithms that are part of Eclipse version 8.5: Pencil Beam Convolution and Analytical Anisotropic Algorithm. Comparing doses at the same point, with and without heterogeneities, percentages of 12% were found when heterogeneity correction was not used. These results also show which of the algorithms approaches better to the experimental values, becoming more reliable.

During image guided interventional radiology (IR) procedures, acute X-ray induced skin injuries may occur due to high absorbed patient skin dose. These procedures are highly dependent on X-ray imaging both for guiding fluoroscopy and high quality diagnostic image acquisitions. A dose metric that quantifies the peak absorbed skin dose (PSD) is therefore of great importance, both in terms of patient specific follow-up and for imaging protocol optimization. Presently, the cumulative interventional reference point (IRP) air Kerma is the most common skin dose estimation metric in use. This metric lacks several important dose contributions, such as pre-patient attenuation, air-to-skin medium correction, scattering from the patient and the support table, and fluence correction for actual source-to-skin distance. In this manuscript, we present a novel methodology for estimating the maximum absorbed skin dose by using dose related X-ray equipment parameters, such as peak tube voltage, support table position and IRP air Kerma obtained from radiation dose structured reports (RDSR) generated by modern IR equipment. In particular, Siemens Artis Zee (Siemens Healthineers, Erlangen, Germany) and Philips Allura Clarity (Philips, Amsterdam, Netherlands). The calculation process was automated by the development of a series of programming scripts in the PythonTM programming language v3.6 (Python Software Foundation), together with a database storing correction factors and machine specific parameters such as half-value layer (HVL). The proposed calculation model enables the implementation of a dose metric which corresponds better to absorbed skin dose than IRP air Kerma in clinical settings. However, extensive future work is required for a complete PSD implementation, in particular, the development of a skin dose map in which the spatial location of each irradiation event is tracked.

Orientador: Carlos Frederico de Oliveira Graeff / Coorientador: Erika Soares Bronze-Uhle / Banca: Francisco Eduardo Gontijo Guimarães / Banca: Marco Antonio Rodrigues Fernandes / O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem carater institucional e integra as atividades de pesquisa em materiais de diversos campi / Resumo: Este trabalho teve como objetivo estudar as características dosimétricas do polímero "poly-[1,1-bis(ethynyl)-4,4-bipheny(bis-tributylphosphine)Pt(11)]" (Pt-DEBP) frente à radiação gama. Para realização dos experimentos dissolveu-se o polímero Pt-DEBP, contendo dez unidades monoméricas, em solventes orgânicos - clorofórmio e totueno. As amostras foram irradiadas em quatro concentrações (0,0500; 0,0375; 0,0250; 0,0113 mg/mL) e em duplicatas, com doses que variaram de 1 a 90 Gy. Os resultados foram avaliados com base em técnicas espectroscópias, como a espectroscopia de absorção óptica (UV-VIs), fluorescência (emissão), fluorescência com resolução temporal (FRT) e infravermelho com transformada de Fourier (FTIR). Para soluções de Pt-DEBP em clorofórmio, nota-se uma alteração na posição da banca principal (л-л *) de absorção óptica para menores comprimentos de onda (blue-shift), aliado a uma diminuição da intensidade de absorção, á medida em que se aumenta a dose de radiação. Na espectroscopia de fluorescência, observou-se um deslocamento para maiores comprimentos de onda (red-shift) aliado a um aumento de intensidade na banda de emissão com aumento da dose de radiação. Experimentos de FRT, das amostras irradiadas em clorofórmio indicam a presença de um novo centro emissor. Os espectros de infravermelho com transformada de Fourier (FTIR) comprovam a entrada de cloro na cadeia polimérica, justificando o blue-shift obervado nos espectros de absorção e o novo centro emissor responsável pela alteração nos espectros de emissão. Além disso, foi analisado o comportamento linear dos resultados obtidos nos estudos de absorção e fluorescência, tomando como base a relação entre comprimento de onda máxima de absorção com a dose e, para o segundo caso, a relação entre... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work aimed to study the dosimetric characteristics of the polymer of the polymer"poly-[1,1-bis (ethynyl) -4,4 biphenyl (bis-tributylphosphine) Pt (II)]" (Pt-DEBP) compared to radiation gamma. The Pt-DEBP polymer, containing ten monomer units, was then dissolved in organic solvents as chloroform and toluene. The samples were irradiated at four concentrations (0.0500, 0.250, 0.0113 mg / mL) in duplicate, with radiation doses ranging from 1 to 90 Gy. The results were evaluated based on spectroscopic techniques such as optical absorption spectroscopy (UV-Vis), fluorescence (emission), time resolved fluorescence (FRT) and Fourier transform infrared (FTIR). For DEBP-Pt solutions in chloroform, there is a shift in the position of the main optical absorption band (л-л *) to lower wavelength (blue-shift), allied to a decreasing absorption intensify with increasing radiation dose. In fluorescence spectroscopy, there was a shift to longer wavelengths (red-shift) allied to an increasing emission intensify with increasing radition dose. FRT experiments on irradiated samples dissolved in chloroform indicated the presence of a new emitter center. FTRI spectra show the incorporation of chlorine in polymer chain, justifying the blue-shift observed in the absorption spectra and the new emission center. In addition, the behavior of linear results in the aborption and fluorescence studies was investigated based on the relationship between the wavelength of maximum absorption/emission and the radiation dose. For both cases, a linear behavior was observed in relation to the sample concentration. Repeatability and stability tests were also performed. For the samples dissolved in tolluene, there was no significant shift of the spectrum of absorption or fluorescence for all doses. The results show that the Pt-DEBP polymer dissolved in chloroform can be used as a dosimer for y-ray doses between... (Complete abstract click electronic access below) / Mestre

Radiation therapy, one of the most common forms of cancer treatment, is continually evolving with the introduction of new technology, more complex treatments and more advanced radiation dose calculations. To ensure the effectiveness and safety of modern radiation therapy, dose measurement tools must improve to accommodate these advances. X-ray computed tomography (CT) polymer gel dosimetry is a unique type of dosimeter that has many advantages and the potential to address some of the challenges in the verification of dose delivery and calculation in radiation therapy. This dissertation investigates the advancement of an x-ray CT polymer gel dosimetry system for use in clinical applications and in particular for deformable dose verification. The first part of this work consists of a reproducibility study of an established x-ray CT polymer gel dosimetry system in an effort to determine the accuracy and precision of dose measurements made with this system and the feasibility of interbatch and generic calibration. Gel measurements were found to have excellent agreement with Monte Carlo dose calculation when using a generic calibration curve. The excellent dosimetric and spatial accuracy established in this study suggest that this dosimetry system is ideally suited for the measurement of high-dose fractionation treatments such as stereotactic radiosurgery (SRS) or stereotactic body radiation therapy (SBRT). The second stage was the development and characterization of the first deformable x-ray CT polymer gel dosimetry system. This study established the setup reproducibility, deformation characteristics and dose response of the new deformable system. The dose response was found to be similar to that of the non-deformable system with similar dosimetric and spatial accuracy when compared to Monte Carlo dose calculation. The system was also found to have sub-millimetre setup reproducibility and the deformable dosimeter was found to reproducibly deform and relax for external compression of up to 30 mm and over 100 consecutive compressions. This work established several important characteristics of the new deformable dosimetry system and it shows excellent potential for use in the evaluation of deformable dose accumulation algorithms. The final component of this dissertation was the use of the newly developed deformable dosimetry system in the evaluation of a novel deformable dose accumulation algorithm, defDOSXYZ. Gel measurements and defDOSXYZ showed excellent agreement in the case of a static control case and this set a benchmark for deformable dose measurements. Measurements of deformed dose by the gel dosimeter showed significant disagreement with dose deformed by defDOSXYZ and the dosimetric differences were well outside the uncertainties established in the first two studies of this dissertation. The results from this study provided some insight into potential avenues of improvement for both the deformable dose calculation and deformable dose measurements. These results were also the first example of deforming dose measured by an x-ray CT read out gel dosimetry system. Overall, the results in this dissertation represent a significant advancement in x-ray CT polymer gel dosimetry and establish its suitability for several clinical applications. / Graduate / 2019-12-06