Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2007. / Dr. Armin J. Ansari, Committee Member ; Dr. Farzad Rahnema, Committee Member ; Dr. Rebecca Howell, Committee Member ; Dr. Nolan E. Hertel, Committee Chair.

Thesis (Ph. D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 14, 2007) Vita. Includes bibliographical references.

A especialidade de Prótese Buco-Maxilo-Facial é responsável por reconstruções complexas da face e do crânio. Entretanto, com a utilização de impressões convencionais, é difícil se alcançar uma adequada adaptação clínica para a reabilitação do paciente. Assim, algumas vêzes, faz-se necessária a obtenção de modelos tridimensionais (3D) que reproduzam a realidade clínica. O objetivo deste estudo é comparar os protótipos obtidos com diferentes protocolos de aquisição de imagem provenientes de distintos aparelhos de tomografia computadorizada com relação à rugosidade superficial, área reconstruída e dose de exposição gerada, procurando estabelecer o mais adequado para a confecção de protótipos de crânio. Para isso, nove protótipos de um fragmento craniofacial seco foram confeccionados. A comparação entre os protótipos quanto à lisura superficial e à área reconstruída foi realizada por meio da Análise de Variância (ANOVA). Nos casos em que a avaliação indicou diferença significativa, foi aplicado como complemento o Teste de Comparações Múltiplas de Tukey. O nível de significância adotado foi de 5%. Em relação à análise de rugosidade as diferenças encontradas não demonstraram correlação com a área reconstruída. Já em relação aos diferentes protocolos, diferenças significativas foram observadas nos protótipos com respeito à área reconstruída e dose de radiação gerada. Pode-se concluir, frente aos resultados encontrados, que as imagens geradas pelos tomógrafos de feixe cônico e feixe em leque, utilizando os protocolos com as resoluções máximas estudadas, estão indicadas para a confecção de protótipos. Contudo, o que deve nortear a seleção do melhor protocolo tomográfico deve ser o propósito da indicação clínica correlacionado com o princípio ALARA (As Low As Reasonably Achievable). / Oral-maxillo-facial prosthodontics is the study of complex face and skull reconstructions. In view of the insufficient degree of adjustment of conventional impression to enable proper clinical rehabilitation, among other reasons, practitioners increasingly resort to 3D models that accurately reproduce the clinical reality. The aim of this study is to determine the optimal selection of imaging device and protocol for use in skull prototyping. The surface roughness and reconstructed area of nine prototypes obtained from a dried craniofacial specimen using different image acquisition protocols and CT devices were measured, in addition to measurements of the radiation dose potentially received by the patient. ANOVA of the surface roughness, reconstructed area and radiation dose data enabled statistical comparisons among the prototypes. Where significant differences were found, Tukey’s multiple-comparison test was conducted, using a significance level of 5%. No correlation was found between surface roughness and reconstructed area. However, significant differences in reconstructed area and radiation dose were found among the different protocols. These results support the use of images generated by CBCT or fan beam CT for the construction of prototypes, using the protocols with the highest resolution. Nevertheless, the selection of the most appropriate TC protocol should be based on the particular clinical indication along with the ALARA (as low as reasonably achievable) principle.

A especialidade de Prótese Buco-Maxilo-Facial é responsável por reconstruções complexas da face e do crânio. Entretanto, com a utilização de impressões convencionais, é difícil se alcançar uma adequada adaptação clínica para a reabilitação do paciente. Assim, algumas vêzes, faz-se necessária a obtenção de modelos tridimensionais (3D) que reproduzam a realidade clínica. O objetivo deste estudo é comparar os protótipos obtidos com diferentes protocolos de aquisição de imagem provenientes de distintos aparelhos de tomografia computadorizada com relação à rugosidade superficial, área reconstruída e dose de exposição gerada, procurando estabelecer o mais adequado para a confecção de protótipos de crânio. Para isso, nove protótipos de um fragmento craniofacial seco foram confeccionados. A comparação entre os protótipos quanto à lisura superficial e à área reconstruída foi realizada por meio da Análise de Variância (ANOVA). Nos casos em que a avaliação indicou diferença significativa, foi aplicado como complemento o Teste de Comparações Múltiplas de Tukey. O nível de significância adotado foi de 5%. Em relação à análise de rugosidade as diferenças encontradas não demonstraram correlação com a área reconstruída. Já em relação aos diferentes protocolos, diferenças significativas foram observadas nos protótipos com respeito à área reconstruída e dose de radiação gerada. Pode-se concluir, frente aos resultados encontrados, que as imagens geradas pelos tomógrafos de feixe cônico e feixe em leque, utilizando os protocolos com as resoluções máximas estudadas, estão indicadas para a confecção de protótipos. Contudo, o que deve nortear a seleção do melhor protocolo tomográfico deve ser o propósito da indicação clínica correlacionado com o princípio ALARA (As Low As Reasonably Achievable). / Oral-maxillo-facial prosthodontics is the study of complex face and skull reconstructions. In view of the insufficient degree of adjustment of conventional impression to enable proper clinical rehabilitation, among other reasons, practitioners increasingly resort to 3D models that accurately reproduce the clinical reality. The aim of this study is to determine the optimal selection of imaging device and protocol for use in skull prototyping. The surface roughness and reconstructed area of nine prototypes obtained from a dried craniofacial specimen using different image acquisition protocols and CT devices were measured, in addition to measurements of the radiation dose potentially received by the patient. ANOVA of the surface roughness, reconstructed area and radiation dose data enabled statistical comparisons among the prototypes. Where significant differences were found, Tukey’s multiple-comparison test was conducted, using a significance level of 5%. No correlation was found between surface roughness and reconstructed area. However, significant differences in reconstructed area and radiation dose were found among the different protocols. These results support the use of images generated by CBCT or fan beam CT for the construction of prototypes, using the protocols with the highest resolution. Nevertheless, the selection of the most appropriate TC protocol should be based on the particular clinical indication along with the ALARA (as low as reasonably achievable) principle.

Carbon-doped aluminium oxide, α-Al₂O₃:C, is a ultra-sensitive dosimeter of topical research interest. The aim of this project was to investigate the dynamics of luminesce in this material. The methods of investigation consisted of thermoluminescence and time-resolved optical stimulation. Thermoluminescence measurements provide information on trap distribution and kinetic parameters of the traps involved in luminescence whereas time-resolved optical stimulation is a handy technique in investigation of luminescence lifetimes and provides an insight into the charge transitions between traps and recombination centres. Measurements were made on samples annealed at a nominal temperature of 900⁰C for 15 minutes. The material shows the presence of five thermoluminescence peaks at 37⁰C, 160⁰C, 300⁰C 410⁰C, and 480⁰C at a heating rate of 0.03k/s when irradiated to 6.0 Gy of beta. The main peak at 160⁰C, shows a linear dose response for doses between 0.1 Gy and 10 Gy and then goes sublinear above 10 Gy, the peak at 37⁰C shows a sublinear dose response for doses between 0.1 Gy and 10 Gy and appears to saturate thereafter, whereas the dose response of the peak at 300⁰C goes from linear to supralinear then apparently quadratic behaviour in the dose range of 0.1 Gy to 16.0 Gy. The trap depth of the main peak, that is, its activation energy as determined below the conduction band, has been approximated at 1.3 eV with a kinetic order of approximately 1.2. Time-resolved optical stimulation has been used to investigate luminescence lifetimes. The mean luminescence lifetime obtained for the sample at ambient temperatures is 35.0±1.0 ms. The investigations of the dependence of luminescence lifetimes on measurement temperature show that the material suffers from thermal quenching effects at measurement temperatures above 140⁰C with the activation energy of thermal quenching estimated at 1.045±0.002 eV. Shallow traps i.e. traps lying close to the conduction band, seem to elongate the lifetimes of optically stimulated luminescence in the material at temperatures between 30⁰C - 80⁰C due to charge retrapping. The material exhibits both fading and recuperation of the optically stimulated luminescence signal with storage time.

Magister Scientiae - MSc / The Environmental Radioactivity Laboratory (ERL) at iThemba LABS undertakes experimental work using a high purity germanium (HPGe) detector for laboratory measurements. In this study the Monte Carlo transport code, MCNPX, which is a general-purpose Monte Carlo N − Particle code that extends the capabilities of the MCNP code, developed at the Los Alamos National Laboratory in New Mexico, was used. The study considers how various parameters such as (1) coincidence summing, (2) volume, (3) atomic number (Z) and (4) density, affects the absolute photopeak efficiency of the ERL’s HPGe detector in a close geometry (Marinelli beaker) for soil, sand, KCl and liquid samples. The results from these simulations are presented here, together with an intercomparison exercise of two MC codes (MCNPX and a C++ program developed for this study) that determine the energy deposition of a point source in germanium spheres of radii 1 cm and 5 cm. A sensitivity analysis on the effect of the detector dimensions (dead layer and core of detector crystal) on the photopeak detection efficiency in a liquid sample and the effect of moisture content on the photopeak detection efficiency in sand and soil samples, was also carried out. This study has shown evidence that the dead layer of the ERL HPGe detector may be larger than stated by the manufacturer, possibly due to warming up of the detector crystal. This would result in a decrease in the photopeak efficiency of up to 8 % if the dead layer of the crystal were doubled from its original size of 0.05 cm. This study shows the need for coincidence summing correction factors for the gamma lines (911.1 keV and 968.1 keV) in the 232Th series for determining accurate activity concentrations in environmental samples. For the liquid source the gamma lines, 121.8 keV, 244.7 keV, 444.1 keV and 1085.5 keV of the 152Eu series, together with the 1173.2 keV and 1332.5 keV gamma lines of the 60Co, are particularly prone to coincidence summing. In the investigation into the effects of density and volume on the photopeak efficiency for the KCl samples, it has been found that the simulated results are in good agreement with experimental data. For the range of sample densities that are dealt with by the ERL it has been found that the drop in photopeak efficiency is less than 5 %. This study shows that the uncertainty of the KCl sample activity measurement due to the effect of different filling volumes in a Marinelli beaker is estimated in the range of 0.6 % per mm and is not expected to vary appreciably with photon energy. In the case of the effect of filling height on the efficiency for the soil sample, it was found that there is a large discrepancy in the trends of the simulated and experimental curves. This discrepancy could be a result of the use of only one sand sample in this study and therefore the homogeneity of the sample has to be investigated. The effect of atomic number has been found to be negligible for the soil and sand compositions for energies above 400 keV, however if the composition of the heavy elements is not properly considered when simulating soil and sand samples, the effect of atomic number on the absolute photopeak efficiency in the low energy (< 400 keV) region can make a 14 % difference. / South Africa

Magister Scientiae - MSc / The natural 238U, 232Th and 40K radioactive content of vineyard soil was measured with an in-situ gamma-ray detector. The activity concentrations measured with the in-situ detector are normalized using the laboratory-determined activity concentrations of several samples from the vineyard site. To determine the activity concentration of a particular soil sample, the gamma-ray photopeak detection efficiencies are required. In this work, the detection efficiencies were derived for each soil sample using gamma-ray photopeaks associated with the radionuclides of 238U and 232Th present in the sample, and the 40K, 1460.8 keV gamma-ray peak, from KCl salt. The systematic effects related to the gamma ray photopeaks used, the sample moisture and sealing, sample volume or filling height, and sample density, were determined and applied in order to obtain the accurate sample activity concentrations. Assessment of the effect of using specific gamma photopeaks on the activity concentrations was done to confirm that the gamma-ray photopeaks highly prone to coincidence summing were omitted from the efficiency analysis. The effect of sample moisture and sealing suggested that in order to optimize the accuracy of each radioactivity measurement each sample must be oven dried and then hermitically sealed. The effect of volume or filling height variations of 0.47 % per mm between the sample and KCl standard was derived and this figure was incorporated into the uncertainty in each of the sample activity concentrations. The effect of density variations of less than 5 %, for sample densities ranging from 0.7 g.cm-3 to 1.6 g.cm-3, was determined and incorporated in the efficiency analysis and activity concentration uncertainties. After taking into account all these systematic effects, the soil sample activity concentration uncertainty was found to be no more than 10.4 % at the 95 % confidence level. / South Africa

La simulation numérique est un outil indispensable pour la résolution de problèmes électromagnétiques. Le temps de calcul ainsi que la précision des résultats dépendent du niveau de description utilisé et des dimensions électriques du problème analysé. Dans le cas de figure où il est nécessaire de modéliser un environnement électriquement grand, l'emploi de méthodes classiques comme la méthode des différences finies dans le domaine temporel (FDTD) se heurte à des difficultés en termes de temps de simulation. Cet aspect devient particulièrement problématique quand l'analyse doit être menée pour plusieurs valeurs d'un ou plusieurs paramètres définissant le problème étudié. Face à cette variabilité et afin d'éviter la multiplication de simulations coûteuses, Il est nécessaire d'opter pour des méthodes appropriées. Les travaux de cette thèse sont consacrés au développement d'une nouvelle approche permettant de résoudre de manière efficace l'aspect variable rencontré dans un problème multiéchelle. Cette nouvelle méthode issue de l'association de la FDTD à Grille Double (DG-FDTD) avec un modèle de substitution se nomme la MM-DG-FDTD (Macro-Modèle basé sur la DG-FDTD). L'emploi de la DG-FDTD vise à traiter l'aspect multi-échelle en divisant le problème étudié en sous-volumes FDTD possédant chacun ses propres paramètres de simulation. L'utilisation d'un modèle de substitution rapide construit en peu de simulations électromagnétiques permet de remplacer rigoureusement et rapidement la dernière simulation de la DGFDTD. Après avoir validé le bon fonctionnement du modèle de substitution sur des cas simples, une utilisation de la MM-DGFDTD est effectuée sur deux applications inscrites dans deux contextes : la dosimétrie numérique et le couplage entre antennes. La première propose d'estimer la valeur du champ électrique à l'intérieur de l'oeil gauche d'un modèle de corps humain. Ce dernier est soumis au rayonnement électromagnétique d'une antenne localisée sur un véhicule. Cette étude est effectuée pour un grand nombre de positions du corps autour du véhicule. La seconde application consiste à évaluer la valeur du coefficient de transmission entre deux antennes ULB (Ultra-Large Bande). La position de l'antenne de réception évolue au sein d'un grand environnement. Pour ces deux études, la MM-DG-FDTD montre sa capacité à donner des résultats rapides et précis en comparaison d'une utilisation classique de la DG-FDTD. / Numerical modelling is an essential tool for solving electromagnetic problems. The computation time and the accuracy of the results depend on the description level used and electrical dimensions of the analyzed problem. When it is necessary to model an electrically large environment, the use of conventional methods such as the finite difference time domain (FDTD) face difficulties in terms of simulation time. This becomes particularly problematic when the analysis must be carried out for several values of one or more parameters defining the studied problem. Considering this variability aspect and in order to avoid multiplication of costly simulations, it is necessary to choose suitable methods. This thesis aims to develop a new approach to solve effectively the variable feature encountered in some multi-scale problems. This new method called the MM-DG-FDTD (MacroModel based Dual Grid-FDTD) results from the association of the Dual Grid- FDTD (DG-FDTD) method with a substitution model. The use of the DG-FDTD permits to treat multiscale aspect dividing the studied problem into FDTD sub-volumes. Each step has its own simulation parameters. The fast substitution model built in few electromagnetic simulations replaces in a rigorous and efficient way the last expensive DG-FDTD simulation. The proper operation of the substitution model is firstly validated using simple cases. Next, a use of the MM-DG-FDTD is performed on two applications belonging to two contexts: numerical dosimetry and antennas coupling. The first one proposes to estimate the value of the electric field inside the left eye of a human body model. It receives electromagnetic radiation from an antenna located onboard a vehicle. This study is carried out for a large number of positions of the body around the vehicle. The second application is to assess the value of the transmission coefficient between two UWB (Utra-Wide Band) antennas. The position of the receiving antenna changes in a large environment. For both studies, MM-DG-FDTD shows its ability to give fast and accurate results compared to a classic use of the DG-FDTD.

Le cancer du sein est le cancer le plus fréquent chez la femme, touchant une femme sur dix, selon la zone géographique. L’irradiation partielle et accélérée du sein (IPAS) constitue un nouveau concept d’irradiation postopératoire du sein après chirurgie conservatrice pour cancer à faible risque de rechute locale. Dans le premier chapitre de cette thèse, nous discutons les rationnelles de l’utilisation de la méthode IPAS comme une alternative à l’irradiation totale du sein ainsi que ses principes et les avantages et inconvénients des différentes techniques utilisée. L’une de ces techniques est la curiethérapie interstitielle à haut débit de dose (HDD). La curiethérapie interstitielle de haut débit de dose est la technique d’irradiation partielle et accélérée du sein qui bénéficie du suivi le plus important, avec des résultats encourageants. La précision du système de planification de traitement (TPS) dans la localisation de la source et le calcul de la dose est absolument nécessaire pour assurer l’administration de la dose prévue. L’Intégrale de Sievert et le formalisme TG43 fournissent des méthodes rapides et simples pour vérifier la dose calculée par le TPS. Dans le deuxième chapitre, nous discutons un outil de vérification et d’optimisation de dose calculée pour l’IPAS en HDD. Cet outil permet de simuler une dose à partir des paramètres définis par le physicien. Souvent, le radiothérapeute effectue un recalage mental pour traduire les positions des cathéters, simulés sur les images CT de planification, en positions réelles dans le sein. Cette opération peut induire des erreurs à cause des différences de forme et de position du sein sur l’échographie per-opératoire, par rapport à celles du CT de planification. Dans le troisième chapitre de la thèse, nous proposons une méthode de recalage des données de planification et de l’échographie de guidage per-opératoire comme une solution qui permettra de reporter de manière automatique les données de planification sur la grille de curiethérapie installée, et visualiser le tout sur les moniteurs de contrôle. La technique IPAS est considérée comme une méthode invasive et coûteuse pour des raisons de radioprotection. La thermothérapie par laser interstitiel (LITT) est une technique ablative, mini-invasive, et en cours d’évaluation. La LITT provoque une zone de nécrose de coagulation dont le volume doit être contrôlé tout en réduisant les effets sur les tissus adjacents. Dans le quatrième chapitre, nous présentons les résultats préliminaires de la simulation de la distribution de la chaleur et de dommage thermique de l’application la méthode LITT pour la thérapie focale du cancer du sein. / Breast cancer is the most common in women, affecting one in ten women, by geographic area. Accelerated Partial Breast Irradiation (APBI) is a new concept of postoperative irradiation after breast conserving surgery for cancer at low risk of local recurrence. In the first chapter of this thesis, we present the rational use of the APBI method as an alternative to the whole breast irradiation and then we discuss the principles, the benefits, and the drawbacks of the different techniques used. One of these techniques is the multicatheters high dose rate (HDR) interstitial brachytherapy. Multicatheter interstitial brachytherapy was the originally employed APBI technique and as a consequence has generated clinical experience with the longest follow-up duration, and with encouraging results.The accuracy of treatment planning system (TPS) in the source location and the dose calculation is absolutely necessary to ensure the planned dose. Sievert Integral and TG43 formalism provide quick and easy methods to check and to verify the dose calculated by the TPS. In the second chapter, we discuss a dose calculation and optimization tool for the APBI method using HDR sources. This tool simulates the dose from the parameters defined by the physicist. Often, the radiotherapist performs during the procedure a mental re-adjustment of catheters positions simulated on the CT images. This operation could lead to errors due to differences in breast form and catheters positions on the intra-operative ultrasound images compared to the planed one on CT images. In chapter three of this thesis, we propose a registration method between data from planning and the one from intra-operative ultrasound images as a solution that will allow to the radiotherapist to report planning data automatically on the brachytherapy template to viualize all data on the computer monitor. The APBI technique is considered an invasive ans expensive method due to radiation protection reasons. Laser Interstitial Thermotherapy (LITT) is minimally invasive ablative technique, and under evaluation. The LITT produces a coagulation nerosis area where the target volume is controlled while minimizing effects on surrounding tissus. In chapter four, we present the preliminary results of simulation of heat and damage distribution from applying the LITT method for focal laser ablation of breast cancer.

Orientadores: Eduardo Tavares Costa, André Oliveira Sawakuchi / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-27T00:20:49Z (GMT). No. of bitstreams: 1 Mineli_ThaysDesiree_M.pdf: 1544477 bytes, checksum: 80869854299a120a6e91842425c1e644 (MD5) Previous issue date: 2015 / Resumo: O uso de radiação ionizante é cada vez mais intenso, seja na indústria seja na área médica. Os efeitos nocivos da radiação ionizante exigem medidas de segurança na sua utilização e um dos meios mais comuns para proteção da saúde do operador de equipamentos que usam esta radiação é o controle da dose que este pode receber em determinado período de tempo. Para tal controle, são normalmente utilizados dosímetros pessoais. Estudos sobre datação de sedimentos costeiros e fluviais do Brasil têm encontrado tipos específicos de quartzo com excelentes características dosimétricas. Com o objetivo de analisar as propriedades dosimétricas de amostras de quartzo de elevada sensibilidade de luminescência e avaliar a sua possível utilização na dosimetria pessoal, foram feitos testes comparativos com amostra do principal e mais utilizado dosímetro pessoal do tipo OSL (Optically Stimulated Luminescence), o Al2O3:C. Este trabalho apresenta as características de luminescência de amostras de quartzo. Essas características foram determinadas por testes de recuperação de dose conhecida (dose recovery) por meio de protocolo de alíquota única (Single-Aliquot Regenerative ¿ SAR) em amostras irradiadas por fonte de radiação beta. Foram realizados testes de sensibilidade e de estabilidade do sinal OSL e testes com radiação gama. Os resultados mostraram que as amostras de quartzo estudadas foram capazes de recuperar com exatidão doses de 50 mGy a 50Gy. Estimou-se que as amostras de quartzo saturam em doses (114-175 Gy) superiores à dose de saturação da amostra de Al2O3:C (35 Gy). A dose mínima capaz de ser medida pelas amostras de quartzo variou de 0,2 mGy (para radiação gama) a aproximadamente 20 mGy (para radiação beta). As amostras de quartzo não apresentaram fading do sinal OSL. O sinal OSL ultravioleta da amostra de Al2O3:C cresceu com o tempo. A amostra de Al2O3:C apresentou maior sensibilidade em comparação às amostras de quartzo no teste com radiação beta. A sensibilidade da amostra de quartzo TE65B no teste com radiação gama foi superior à sensibilidade da amostra Al2O3:C. Estes resultados indicam que as amostras de quartzo estudadas têm potencial como material para dosímetros e incentivam estudos mais aprofundados para avaliar o uso destes tipos de quartzo como elementos sensores em dosímetros pessoais / Abstract: The use of ionizing radiation is becoming more intense, whether in industry or in the medical field. The harmful effects of ionizing radiation require safety measures in its use. One of the most common ways to protect the health of the operator of ionizing radiation equipment is the dose control that he/she can receive in a given time period. Personal dosimeters are used for this purpose. Studies on dating of coastal and fluvial sediments in Brazil have found quartz types with very high luminescence signal and excellent dosimetric characteristics. In order to analyze the dosimetric properties of very bright Brazilian quartz samples and evaluate their use in personal dosimetry, comparative tests with the most used personal OSL (Optically Stimulated Luminescence) dosimeter, Al2O3:C, were made. This work presents the luminescence characteristics of quartz samples. These characteristics were determined by dose recovery tests using a Single-Aliquot Regenerative dose protocol (SAR) in samples irradiated by beta radiation. Sensitivity and stability tests and gamma radiation tests were made. The results have shown that the studied quartz samples were able to recover at least a dose range from 50 mGy to 50 Gy. It was estimated that the quartz samples saturate in doses (114-175 Gy) above the saturation dose of Al2O3:C sample (35 Gy). The minimum dose capable of being measured by the quartz samples ranged from 0.2 mGy (for gamma rays) to about 20 mGy (for beta radiation). The quartz samples showed no fading of the OSL signal. The ultraviolet OSL signal of Al2O3:C sample increased with time. The Al2O3:C sample showed higher sensitivity compared to quartz samples in beta radiation test. However, the sensitivity of TE65B quartz sample for the gamma radiation test was higher than the sensitivity of the Al2O3:C sample. These results indicate that the studied quartz samples have potential as dosimeter material and encourage further studies to evaluate the use of this type of quartz as sensor element in personal dosimeters / Mestrado / Engenharia Biomedica / Mestra em Engenharia Elétrica