Depuis deux décennies, les nombreux développements des techniques de radiothérapie par modulation d’intensité (RCMI) ont permis de mieux conformer la dose au volume cible et ainsi, d’augmenter les taux de réussite des traitements des cancers. Ces techniques ont souvent l’avantage de réduire la dose aux organes à risque proches de la zone traitée, mais elles ont l’inconvénient d’apporter un niveau de dose périphérique plus important que les techniques basiques sans modulation d’intensité. Dans ce contexte, l’augmentation du taux de survie des patients qui en résulte, accroît également la probabilité de manifestation d’effets iatrogènes dus aux doses périphériques (tels que les cancers secondaires). Aujourd’hui, la dose périphérique n’est pas considérée lors de la planification du traitement et il n’existe aucun outil numérique fiable pour sa prédiction. Il devient cependant indispensable de prendre en compte le dépôt de dose périphérique lors de la planification du traitement, notamment dans les cas pédiatriques. Cette étude doctorale a permis la réalisation de plusieurs étapes du développement d’un outil numérique, précis et rapide, de prédiction de la dose hors-champ fondé sur le code Monte Carlo PENELOPE. Dans cet objectif, nous avons démontré la capacité du code PENELOPE à estimer la dose périphérique en comparant ses résultats avec des mesures de référence réalisées à partir de deux configurations expérimentales (métrologique et pré-clinique). Ces travaux expérimentaux ont notamment permis la mise en place d’un protocole d’utilisation des dosimètres OSL pour la mesure des faibles doses. En parallèle, nous avons pu mettre en évidence la convergence lente et rédhibitoire du calcul en vue d’une utilisation clinique. Par conséquent nous avons réalisé un travail d’accélération du code en implémentant une nouvelle technique de réduction de variance appelée transport pseudo-déterministe spécifiquement dédiée à l’amélioration de la convergence dans des zones lointaines du faisceau principal. Ces travaux ont permis d’améliorer l’efficacité des estimations dans les deux configurations de validation définies (gain d’un facteur 20) pour atteindre des temps de calcul raisonnables pour une application clinique. Des travaux d’optimisation du code restent à entreprendre de façon à améliorer encore la convergence de l’outil pour ensuite en envisager une utilisation clinique. / Over the last two decades, many technical developments have been achieved on intensity modulated radiotherapy (IMRT) and allow a better conformation of the dose to the tumor and consequently increase the success of cancer treatments. These techniques often reduce the dose to organs at risk close to the target volume; nevertheless they increase peripheral dose levels. In this situation, the rising of the survival rate also increases the probability of secondary effects expression caused by peripheral dose deposition (second cancers for instance). Nowadays, the peripheral dose is not taken into account during the treatment planification and no reliable prediction tool exists. However it becomes crucial to consider the peripheral dose during the planification, especially for pediatric cases. Many steps of the development of an accurate and fast Monte Carlo out-of-field dose prediction tool based on the PENELOPE code have been achieved during this PhD work. To this end, we demonstrated the ability of the PENELOPE code to estimate the peripheral dose by comparing its results with reference measurements performed on two experimental configurations (metrological and pre-clinical). During this experimental work, we defined a protocol for low doses measurement with OSL dosimeters. In parallel, we highlighted the slow convergence of the code for clinical use. Consequently, we accelerated the code by implementing a new variance reduction technique called pseudo-deterministic transport which is specifically with the objective of improving calculations in areas far away from the beam. This step improved the efficiency of the peripheral doses estimation in both validation configurations (by a factor of 20) in order to reach reasonable computing times for clinical application. Optimization works must be realized in order improve the convergence of our tool and consider a final clinical use.

Ce travail de thèse a pour but de développer et de caractériser de nouveaux systèmes d'assurance qualité en curiethérapie, à base de sondes dosimétriques en Nitrure de Gallium (GaN). L'étude comprend d'une part la caractérisation et la simulation du transducteur GaN et de la sonde dosimétrique, et d'autre part la mise en œuvre et les tests de 2 systèmes d'assurance qualité.Les propriétés de radioluminescence du transducteur GaN ont été étudiées afin d'optimiser le signal dosimétrique des sondes. La sonde dosimétrique encapsulant un petit volume de cristal GaN a ensuite été caractérisée en vue de son intégration dans des systèmes d'assurance qualité. Des simulations Monte Carlo sur la sonde GaN ont également été effectuées et comparées aux mesures.Pour l'assurance qualité en curiethérapie, nous avons proposé une méthode utilisant plusieurs sondes GaN, pour permettre de déterminer en temps réel les principaux paramètres physiques d'un projecteur de source : la position, le temps de pause et l'activité de la source. Nous avons conçu et réalisé deux prototypes de systèmes d'assurance qualité mettant en œuvre cette méthode : un fantôme instrumenté pour le contrôle prétraitement et un applicateur gynécologique instrumenté pour le contrôle pendant le traitement. Ces deux prototypes ont été testés en conditions cliniques, et leurs principales caractéristiques sont satisfaisantes. Ils répondent aux besoins applicatifs et offrent une perspective intéressante pour de nouveaux outils de contrôle qualité en curiethérapie / This work aims to develop and characterize novel quality assurance systems based on Gallium Nitride (GaN) dosimeter probe for brachytherapy. It includes characterization and simulation studies of the GaN transducer and of the dosimeter probe as well as the implementation and testing of two quality assurance system prototypes.The radioluminescence properties of the GaN transducer have been studied for optimization of the dosimeter response. Characterization studies of dosimeter probes incorporating miniaturized GaN transducers have been carried out in the frame of the quality assurance systems development. Monte Carlo simulations of the GaN probe under irradiation has also been performed and compared with measurements.A method which processes simultaneously the output signals from several GaN probes has been proposed for real time determination of the projector’s physical parameters (dwell position, dwell time and activity of the source). Two quality assurance system prototypes implementing this method have been designed and fabricated: an instrumented phantom for pre-treatment quality assurance and an instrumented gynecological applicator for in vivo quality control. These two prototypes have been tested and evaluated in clinical conditions and their main characteristics are satisfactory. Both systems are in line with the application requirements and offers new perspectives for quality assurance in brachytherapy

Measurement of urine absorbance which has been irradiate by a dose of ionising radiation with addition of Mn2+ should serve to find the dose of radiation. This method could work quickly and reliably for homogeneous irradiation of person or as a rough estimate of the dose which the person received during a radiation accident. This method should serve for quick classification of the person. The target of this thesis is to find out if the irradiated urine with the addition of a solution of manganese chloride will change absorbance according to radiation dose. And if urine can be used as a biological dosimeter. In the theoretical part I describe the basic areas related to the topic and target of my thesis. This part is divided to seven subchapters: ionising radiation, radiation protection, radiotherapy, particle accelerators, spectrophotometry, excretion and urine, and dosimetry and its methods. Methods of this thesis are not clear. I tried different procedures during experiments with different results. First, I always prepared samples of urine in tubes and irradiated it in a linear accelerator Clinac 2100C/D in České Budějovice, a.s. hospital with doses from 1 to 25 Gy. Before each measurement I had two sets of tubes with these doses: 0, 1, 2, 3, 5, 7, 10, 15, 20 and 25 Gy. The following procedure was different in each experiment. Sometimes I tried adding a solution of manganese chloride to all tubes at once. Sometimes I tried to adding a solution of manganese chloride to each tube separately. I added the solution to irradiated urine at various concentrations of solution (from 1 do 5 mols) and different amounts (from 1 to 3 ml). Another difference was the use of centrifuges. A centrifuge was use in about half of experiments. Other measurements were made without centrifugation.In discussion I propose recommended methods. I recommend measuring only without centrifuges. Each cell should be measured as soon as possible after irradiation and simultaneously as soon as possible after adding the solution of manganese chloride. Results of the thesis are not clear. Only some experiments which were measuring with centrifuge were clear. I can say that this method does not work when a centrifuge is used at any tested concentration of solution of manganese chloride. The absorbance of single doses of ionising radiation does not change and the values were the same when using 1M, 3M and 5M solutions of MnCl2. The resulting graphs from all experiments have a constant absorbance value of all measured doses. (subchapter 3.1).In the remaining experiments measured without the centrifuge the results were much more interesting. In some experiments the measured absorbance really changed with the dose of ionising radiation so the hypothesis of this study was confirmed. But the differences were too small for this method to be used for measuring radiation doses (subchapter 3.2).The results were compared with the results of the thesis ?Measurement of urine extinction in depending on ionising radiation? from author Š. Radová. She performed a similar experiment, but with a different indicator - FeSO4. 7 H20. It was found that the indicator FeSO4. 7 H20 is preferable to measuring doses of ionising radiation in urine. In conclusion I can say that the hypothesis of this study was confirmed, but the method could not be used in practice and irradiated urine with added MnCl2 indicator does not function as a biological dosimeter.

The introductory part of the diploma thesis primarily focuses on the history of radiotherapy, i.e. what it emerged from and how it developed, as it is one of the most important fields in medicine, especially because thousands of people are irradiated every day due to different tumour and non-tumour diseases. Another reason why ionizing radiation is described is the fact that it is a necessary part of tumour disease irradiation. Ionizing radiation is also connected with radiation protection. This section presents a historical overview of radiation protection, as well as principles and quantities of this field. Furthermore, it focuses on Czech acts, decrees, and government regulations which define various measures governing this issue. Radiation protection forms the basis of patient, workplace, and personnel monitoring. All this is connected with the measurement and evaluation of received personal doses. This brings the thesis to the field of dosimetry, therefore various dosimeters used in practice are described. The aim of this diploma thesis is the measurement of patients? personal doses in head and neck irradiation using the electronic personal dosimeter at the radiotherapy centre of Nemocnice České Budějovice, a. s. The thesis is based on the question of whether irradiation doses that patients with head and neck tumours receive outside the primary radiation beam are negligible. The theoretical part of the thesis uses all available resources from both foreign and Czech literature. The practical part is based on numerical statistics, i.e. a quantitative method. The research was carried out at the radiotherapy centre of Nemocnice České Budějovice, a. s. Irradiation of patients with head and neck tumours was performed on a linear accelerator. Each patient had a mask to which an electronic personal dosimeter was attached during irradiation. Using this dosimeter, it was possible to measure doses received outside the central radiation beam. The measured values were then used to carry out assessment using formulas. Patients who undergo cancer treatment receive relatively high doses of radiation, so my main goal was to measure personal dose equivalents at the reference point. When comparing the percentage of the number of examinations with the web portal Epidemiology of Malignant Tumours in the Czech Republic, it was found that irradiation of the neck is more frequent than irradiation of the head. The total values of personal dose equivalents are relatively high in each patient, but because it is medical treatment, these values are not subject to radiation exposure limits. The comparison of the irradiated areas shows that irradiation of the neck has small values of personal dose equivalents to 1Gy compared to irradiation of the head.

A radiocirugia estereotáxica é uma técnica que fornece altas doses de radiação utilizando campos pequenos para conformação da dose no volume alvo do tratamento. Devido à complexidade desta técnica torna-se necessária a verificação da distribuição de dose no volume de tratamento. Neste trabalho, as distribuições tridimensionais (3D) de doses de casos clínicos de neoplasias cranianas foram estudadas utilizando-se um objeto simulador de cabeça. A reconstrução das distribuições de doses nos volumes alvo e nas regiões adjacentes a estes foram avaliadas com o código de simulação PENELOPE, o dosímetro MAGIC-f gel e com o sistema de planejamento iPlan. Filmes radiocrômicos também foram empregados para a determinação das distribuições de dose em planos do tratamento. As respostas obtidas com as ferramentas dosimétricas utilizadas foram analisadas através de distribuições de índices gama, comparando-se os mapas centrais das distribuições de dose obtidas com as quatro ferramentas dosimétricas utilizadas. Usando-se critérios de tolerância de 3% e 3mm, a análise realizada na região da prescrição de dose (isodoses de 95%) mostrou-se equivalente para todas as ferramentas dosimétricas utilizadas; resultado diferente foi observado para isodoses menores, com uma equivalência máxima de 76,5%. As distribuições volumétricas, obtidas através do PENELOPE, MAGIC-f gel e o iPlan, foram comparadas, ainda, através dos histogramas dose-volume, para cada caso estudado, mostrando que 95% da dose absorvida relativa encontra-se dentro do volume alvo para todos os planos estudados. A probabilidade de controle tumoral, TCP, foi avaliada para os casos de radiocirurgia estudados, a partir das distribuições volumétricas de dose, resultando em uma probabilidade de controle tumoral máxima de 72%, para todos os casos, conforme o modelo matemático de TCP utilizado. Das comparações realizadas pode-se inferir que o dosímetro MAGIC-f gel e o código de simulação PENELOPE-Monte Carlo podem ser utilizados para determinar as distribuições de dose em 3D para a técnica de radiocirurgia estereotáxica. Essas ferramentas dosimétricas podem, dessa forma, auxiliar no comissionamento de unidades de terapia e em verificações 3D de doses do tratamento dos pacientes, permitindo avaliações dentro e ao redor do volume alvo e podendo se tornar ferramentais de rotina nos serviços de radioterapia. / Stereotactic radiosurgery is a technique which delivers high radiation doses using small fields to conform the absorbed dose into the target volume. Due to the complexity of this technique it is necessary to verify the dose distribution in the treatment volume. Thus, in this study the three-dimensional (3D) dose distributions of selected clinical cases of cranial tumors were obtained using a head phantom. The the dose distributions of target volumes and adjacent regions were evaluated with PENELOPE Monte Carlo simulation code, MAGIC-f dosimeter and iPlan® treatment planning system. Radiochromic films were also used to determine the dose distribution on selected plans of the treatment. The obtained results for the proposed dosimetric tools were analyzed by the gamma index distributions, comparing the maps of the central dose distributions obtained with the four dosimetric tools. Using the dose criteria of 3% in 3 mm, the gamma index test showed equivalence in the region of dose prescription (95% isodose) and a different result was observed for lower isodoses, with maximum accordance of 76.5%. The volumetric dose distributions obtained with PENELOPE, MAGIC-f and iPlan were also compared using the dose-volume histograms for each studied case, showing that 95% of the absorbed dose yield within the target volume. The tumor control probability, TCP, was evaluated for the studied radiosurgery cases, from the dose distributions-volumetric, resulting in a maximum probability of tumor control of 72% for all cases, for the used mathematical model of TCP. From the results it can be inferred that the MAGIC-f gel dosimeter and the PENELOPE Monte Carlo simulation code can be used to determine 3D dose distributions for stereotactic radiosurgery. These dosimetric tools can assist the commissioning of treatment units and 3D dose verifications of patients treatments, allowing assessments in and around the target volume and may become routine in radiotherapy services.

This master’s thesis deals with the problematics of influence of ionizing radiation on semiconductor devices and their properties. The aim of the thesis is to analyze the different types of radiation that can occur in the areas of application of these components. In the second part, the degradation processes are explored, with emphasis on the influence caused by the radiation dose. Also, the displacement damage and SEE effects are described, but just slightly, because they are not part of this work. The third part describes the device design process and harmful effects, that have to be considered during the design phase. In the forth and the fifth parts of this work were done modeling of radiation effects (influence of dose rate, Single-Event Upset and Total Ionizing Dose) in PSpice program and was carried out the possibility of designing a simple dosimeter with silicon diode. In conclusion, the results of the thesis are summarized and evaluated.

<p>Radiotherapy is used in many clinics to deliver a sufficient and uniform dose to the cancerous tumours while the dose to normal tissues is minimized. However, there is a possibility of missing the target volume due to patient set up/motion errors, or any fluctuation in treatment delivery. Therefore, accurate dose verification tools are essential to evaluate the delivered dose distribution of the designed treatment plan under realistic treatment conditions.</p> <p>Current research is focused on developing 3D dose verification tools to record the complex dose distributions for quality assurance purposes and the evaluation of new treatment techniques. New and novel materials and read-out techniques suitable for use in hospitals are desirable. The objective of this research is to fabricate a transparent radiochromic gel dosimeter that may be used as quality assurance tool. Also, the fabricated gel must be analyzed using a simple optical read-out technique.</p> <p>Gel dosimeters are gels that undergo some chemical changes upon irradiation as a function of absorbed dose. The absorbed dose may be recorded in three dimensions depending on the type of gel dosimeter. Radiochromic gels are dosimeters that change colour upon irradiation. A radiosensitive dye, leucomalachite green (LMG) is dissolved in a matrix material to record the dose distribution in 3D. LMG changes its colour upon irradiation, and has an absorbance band of 629nm.</p> <p>In this research two different matrix materials were investigated: poly (vinyl alcohol) and gelatin. PVA was studied as the primary agent due to its adjustable mechanical strength and high transparency. PVA has also been studied to have a low diffusion rate when it was used as the matrix material in Fricke gel dosimeters [41]. Even though PVA had all the desired characteristics, fabricating a PVA based radiochromic dosimeter was not successful. Consequently, gelatin was used as the matrix material to fabricate a gelatin-based radiochromic dosimeter.</p> <p>Using gelatin, highly transparent radiosensitive gels were successfully fabricated. The absorbencies of the irradiated gels were measured as a function of absorbed dose, using a 1D set up. After, the gels were formed into 5mm thick films and used as two-dimensional dose verification tools. The relationship between absorbance and absorbed dose for 1D measurement was obtained to be 0.00241± 0.00004 , and 0.0022 ± 0.00007 for 2D gels scaled to a thickness of 1 cm.</p> <p>In all of the experiments the absorbance-dose relationships were similar in slopes, but there was an offset between different batches. The offset was 20% between the different experiments. Moreover, there was less than 5% error associated with the physical set up; the major source of error was due to the production and handling of the mixture, possibly due to the effects of inconsistent heating and UV light exposure.</p> <p>The 2D gels were used to verify the dose distribution for the purpose of quality assurance. Six different complicated beams were delivered to the gels and their dose distributions were compared to their respective Pinnacle Calculated Planar (PCP) dose maps. The difference was found to be about 35% at worst; however, this error may be reduced by utilizing more sophisticated data processing methods. Nevertheless, the images were quite similar above 20Gy. Furthermore, the dose distributions recorded by the gels are qualitatively and quantitatively similar to the (PCP) dose map. Although the fabricated gel dosimeters show some promise as future tools for quality assurance purposes, they must go through many more stages of research to be used clinically.</p> / Master of Science (MSc)

Solving radiation shielding problems, i.e. deep penetration problems, is a challenging task from both computation time and resource aspects in field of nuclear engineering. This is mainly because of the complexity of the governing equation for neutral particle transport - Linear Boltzmann Equation (LBE). The LBE includes seven independent variables with presence of integral and differential operators. Moreover, the low successive rate of radiation shielding problem is also challenging for solving such problems. In this dissertation, the Detector Response Function (DRF) methodology is proposed and developed for real-time and accurate radiation shielding calculation. The real-time capability of solving radiation shielding problem is very important for: (1) Safety and monitoring of nuclear systems; (2) Nuclear non-proliferation; and (3) Sensitivity study and Uncertainty quantification. Traditionally, the difficulties of solving radiation problem are: (1) Very long computation time using Monte Carlo method; (2) Extremely large memory requirement for deterministic method; and (3) Re-calculations using hybrid method. Among all of them, the hybrid method, typically Monte Carlo + deterministic, is capable of solving radiation shielding problem more efficiently than either Monte Carlo or deterministic methods. However, none of the aforementioned methods are capable of performing "real-time" radiation shielding calculation. Literature survey reveals a number of investigation on improving or developing efficient methods for radiation shielding calculation. These methods can be categorized by: (1) Using variance reduction techniques to improve successive rate of Monte Carlo method; and (2) Developing numerical techniques to improve convergence rate and avoid unphysical behavior for deterministic method. These methods are considered clever and useful for the radiation transport community. However, real-time radiation shielding calculation capability is still missing although the aforementioned advanced methods are able to accelerate the calculation efficiency significantly. In addition, very few methods are "Physics-based" For example, the mean free path of neutrons are typically orders of magnitude smaller than a nuclear system, i.e. nuclear reactor. Each individual neutron will not travel too far before its history is terminated. This is called the "loosely coupled" nature of nuclear systems. In principle, a radiation shielding problem can be potentially decomposed into pieces and solved more efficient. In the DRF methodology, the DRF coefficients are pre-calculated with dependency of several parameters. These coefficients can be directly coupled with radiation source calculated from other code system, i.e. RAPID (Real-time Analysis for Particle transport and In-situ Detection) code system. With this arrangement, detector/dosimeter response can be calculated on the fly. Thus far, the DRF methodology has been incorporated into the RAPID code system, and applied on four different benchmark problems: (1) The GBC-32 Spent Nuclear Fuel (SNF) cask flooded with water with a $^3$He detector placed on the cask surface; (2) The VENUS-3 experimental Reactor Pressure Vessel (RPV) neutron fluence calculation benchmark problem; (3) RPV dosimetry using the Three-Mile Island Unit-1 (TMI-1) commercial reactor; and (4) A Dry storage SNF cask external dosimetry problem. The results show that dosimeter/detector response or dose value calculations using the DRF methodology are all within $2sigma$ relative statistical uncertainties of MCNP5 + CADIS (Consistent Adjoint Driven Importance Sampling) standard fixed-source calculation. The DRF methodology only requires order of seconds for the dosimeter/detector response or dose value calculations using 1 processor if the DRF coefficients are appropriately prepared. The DRF coefficients can be reused without re-calculations when a model configuration is changed. In contrast, the standard MCNP5 calculations typically require more than an hour using 8 processors, even using the CADIS methodology. The DRF methodology has enabled the capability of real-time radiation shielding calculation. The radiation transport community can be greatly benefited by the development of DRF methodology. Users can easily utilize the DRF methodology to perform parametric studies, sensitivity studies, and uncertainty quantifications. The DRF methodology can be applied on various radiation shielding problems, such as nuclear system monitoring and medical radiation facilities. The appropriate procedure of DRF methodology and necessary parameters on DRF coefficient dependency will be discussed in detail in this dissertation. / Doctor of Philosophy / Since the beginning of nuclear era, enormous amount of radiation applications have been proposed, developed, and applied in our daily life. The radiation is useful and beneficial when they are under control. However, there will be some "unwanted radiation" from these applications, which have to be shielded. For this, radiation shielding has become a very important task. To effectively shield the unwanted radiations, studying the thickness and design of the shields is important. Instead of directly performing experiments, computation is a more affordable and safer approach. The radiation shielding computation is typically an extremely difffficult task due to very limited "communication" between the radiation within the shield and detector outside the shield. In general, it is impractical to simulate the radiation shielding problems directly because the extremely expensive computation resources. Most of interactions of radiation are within the shield while we are only interested in how many of them penetrate through the shield. This is typically called "deep penetration" problems in the radiation transport community.

Em tecidos biológicos lesados, a viscoelasticidade é a propriedade física que mais se modifica em relação ao tecido normal. Palpação manual é geralmente usada para identificar estas lesões, tais como nódulos e cistos. Recentemente, vários estudos envolvendo técnicas ultrassônicas e de ressonância magnética, denominadas elastografia, têm sido empregadas para avaliar as propriedades viscoelásticas dessas lesões. Uma das dificuldades neste tipo de estudo está relacionada ao desenvolvimento de simuladores de tecidos biológicos com inclusões equivalentes, uma vez que, essas estruturas lesadas originam-se a partir do próprio tecido biológico. Com base nessas motivações, técnicas quantitativas de elastografia por ressonância magnética e ultrassom foram exploradas para avaliar lesões simuladas em fantomas viscoelásticos. Estas lesões, com diferentes propriedades viscoelásticas, foram geradas no interior de um fantoma usando radiação ionizante. Os fantomas, também conhecidos como gel dosimétrico, foram desenvolvidos a base de pele animal, e irradiados utilizando um sistema de terapia de radiação convencional. Imagens de relaxometria por ressonância magnética (RRM) foram adquiridas nestes fantomas e usadas como referência padrão da dose absorvida e de sua distribuição. Os perfis da distribuição de dose avaliados nessas imagens de RRM e pelo sistema de planejamento radioterápico TPS 3D foram comparados aos de rigidez das imagens elastográficas. O estudo elastográfico nestes fantomas foi realizado utilizando os métodos de Vibroacustografia (VA), Vibrometria por Ultrassom (VU) e Elastografia por Ressonância Magnética (ERM). O segundo objetivo desta tese foi explorar a viabilidade de existência de speckle em imagens de vibroacustografia. Para testar essa idéia, um modelo tridimensional (3D) para a função de espalhamento de ponto (PSF) do sistema de VA foi simulada. O código da simulação foi desenvolvido em ambiente MATLAB e empregando sub-rotinas do programa Field II para simulação numérica dos transdutores. Imagens de ultrassom modo-B (IUSB) e vibroacustografia foram simuladas usando esse modelo de PSF-3D para um transdutor esférico e confocal, respectivamente. Essas IUSB foram simuladas para servir como um parâmetro comparativo com as imagens geradas por VA. As imagens de ultrassom foram exibidas em um plano tomográfico que corresponde ao plano de imagem da VA. As simulações foram realizadas utilizando um cluster de computadores de alto desempenho. Todas as imagens foram simuladas empregando um modelo de fantoma virtual não homogêneo com dimensões de (10 × 10 × 50) mm3. Os resultados preliminares mostraram um padrão de interferência nas imagens de VA, semelhantes à speckles, obtidas empregando o transdutor confocal. Estas imagens foram produzidas a partir de espalhadores localizados no interior do volume da célula de resolução da PSF-3D. / The viscoelasticity of injured biological tissues is the physical property that changes the most in relation to normal tissue. Manual palpation is commonly used to identify these lesions, such as nodules and cysts. Recently, several studies involving ultrasound and magnetic resonance imaging techniques, called elastography, have been employed to assess the viscoelastic properties of these lesions. One difficulty in this type of study is related to the development of biological tissues mimicking materials with similar inclusions, once these injured structures originate from anomalies within the biological tissue. Based on these motivations, quantitative elastographic techniques based on magnetic resonance and ultrasound modalities have been used to assess injuries in viscoelastic mimicking-tissue phantom materials. These lesions, with different viscoelastic properties, were generated within a phantom using ionizing radiation. The phantoms, also known as dosimeter gel, were developed based on animal skin powder, and irradiated using a conventional radiation therapy system. Magnetic resonance relaxometry images (MRR) were acquired in these phantoms, and were used as absorbed dose standard reference and its distribution. The estimated dose distribution profiles from these images and the ones provided by TPS 3D software radiotherapy planning system were compared to the elastograms. The elastographic studies were conducted using Vibro-acoustography (VA), Magnetic Resonance Elastography (MRE) and Shearwave Dispersion Ultrasound Vibrometry (SDUV) techniques. The second goal of this thesis was to explore the feasibility of speckle existence in vibro-acoustography images. To test that, a three-dimensional (3D) model for the systems point spread function (PSF) was simulated. The simulation code was implemented in MATLAB and using the program Field II subroutines. The numerical simulations were performed using a cluster of high performance computers. B-mode ultrasound and VA images were simulated using that PSF 3D model, for a spherically focused and a confocal transducer, respectively. These B-mode images were simulated as a comparative parameter to the images generated by VA. The B-mode ultrasound images were displayed in a tomographic plane corresponding to the VA imaging plane. All images were simulated using a virtual phantom with dimensions (10 × 10 × 50) mm3. Preliminary results showed a interference pattern in VA images taken with a confocal transducer. These images were produced from scatterers located inside the PSF resolution cell volume.

A Doença Enxerto Contra Hospedeiro Associada à Transfusão (DECH-AT) é uma reação transfusional rara, porém fatal, que ocorre devido à presença de células T no sangue doado e que pode ser prevenida por meio da irradiação do sangue do doador e de seus componentes antes da transfusão. Assim, o controle de qualidade associado à irradiação do sangue é necessário para se garantir a qualidade do produto transfundido. Neste trabalho é proposta a caracterização e a adaptação da resposta do dosímetro Fricke para uso na dosimetria da irradiação de sangue, mais especificamente o Fricke Xilenol Gel (FXG). Este é um dosímetro químico radiocrômico, que apresenta as vantagens de ser tecido equivalente e de permitir a inferência espacial da dose absorvida dentro da faixa de doses usados na prevenção DECH-AT. Dessa maneira, de modo a possibilitar a inferência de dose absorvida em todo o intervalo utilizado na prevenção da DECH-AT (25 a 50 Gy), o FXG foi caracterizado e adaptado para aplicações dosimétricas envolvendo a irradiação de sangue e derivados. Os resultados com o novo dosímetro apontaram adequabilidade para toda a faixa necessária de doses absorvidas, com sensibilidade e desvanecimento temporal satisfatórios para aplicações rotineiras. Além disso, pela metodologia proposta neste trabalho, foi possível determinar as distribuições espaciais das doses absorvidas com o dosímetro proposto de uma maneira rápida e simples, mostrando assim que este dosímetro apresenta características convenientes para o controle de qualidade para a dosimetria da irradiação de sangue e de hemocomponentes. / The Transfusion Associated Graft Versus Host Disease (TA-GVHD) is a rare transfusion reaction, however fatal, which develops due to the presence of donor T lymphocytes in the donated blood and that can be avoided by the irradiation of the donated blood blood and blood components prior to transfusion. Thus, the associated quality control of blood irradiation is necessary to guarantee the quality of the transfused product. In this work it is proposed the characterization and adaptation of the response of a Fricke dosimeter to be used for dosimetry of blood irradiation, more especiafically the Fricke Xylenol Gel (FXG). This is a radiochromic chemical dosimeter, which presents advantages to be tissue equivalent and allows the spatial absorbed dose inference. In this manner, in a way to possibilitate the absorbed dose inference in the full interval used for the prevention of the TA-GVHD (25 to 50 Gy) the FXG was characterized and adapted for dosimetry applications involving blood and blood components irradiation. The results with the new dosimeter showed adequability for the necessary absorbed doses, with satisfactory sensibility and time fading for routine applications. Furthermore, according to the methodology proposed in this work, it was possible to determine the spatial absorbed dose distributions with the new dosimeter in an fast and simple way, showing that this dosimeter presents convenient characteristics for dosimetry quality control of irradiated the blood and blood components.