Este trabalho visa aprimorar e tornar mais precisa a utilização do dosímetro gel polimérico MAGIC-f no estudo da distribuição de dose para fonte radioativas utilizadas na terapia e diagnóstico em medicina nuclear. Para isso foram avaliados os parâmetros de leitura do gel em equipamentos de ressonância magnética e sua resposta quando comparado a resultados obtidos através da utilização do código PENELOPE de simulação Monte Carlo. Dentre as incertezas observadas no processo global da utilização do gel MAGIC-f, sua manufatura foi a que demonstrou uma maior preocupação uma vez que erro na frações de componentes químicos adicionados ocasiona grande diferença na resposta do dosímetro. A aquisição da informação dosimétrica em um equipamento de imagem por ressonância magnética demonstrou que tempos ao eco mais curtos são mais eficientes na diferenciação do sinal gerado no processo de polimerização devido a utilização de fontes de medicina nuclear do que ajustes na resolução da imagem e que a homogeneidade de campo magnético pode ocasionar grande alteração nos valores obtidos. Experimentos realizados com o gel MAGIC-f, demonstraram um baixa dependência energética e um grande dependência com a taxa de dose, dois fatores importantes em medicina, mas resultados simulados e experimentais comparativos utilizando fontes de I-131, Tc-99m e F-18, demonstraram uma grande precisão nos resultados apresentados, tornando assim o gel MAGIC-f uma excelente ferramenta na verificação volumétrica da dose absorvida na terapia com fontes de medicina nuclear. / This work aims to improve and make more accurate use of the gel dosimeter MAGIC-f polymer in the study of dose distribution for radioactive source used in therapy and diagnosis in nuclear medicine. For this, MRI parameters reading of the gel were evaluated and its response when compared to results obtained using a Monte Carlo simulation PENELOPE code. Among the uncertainties observed in the overall use of MAGIC-f gel, its manufacturing demonstrated a greater concern since error in chemical fractions added causes big difference in the response of the dosimeter. The acquisition of dosimetric equipment information in a magnetic resonance imaging showed that the shorter eco times are more efficient in differentiating the signal generated in the polymerization process due to the use of sources of nuclear medicine than image resolution changes and the homogeneity of the magnetic field can cause large difference in the results. Experiments performed with the MAGIC-f gel, demonstrated a low energy dependence and a large dependence on the dose rate, two important factors in nuclear medicine, but comparative results with simulated and experimental processes using sources of I-131, Tc-99m and F-18 showed a great accuracy in results, thus making the MAGIC-f gel an excellent tool for volumetric verification of absorbed dose therapy with sources of nuclear medicine.

A presença de material de alto número atômico adjacente ao tecido mole aumenta localmente a dose absorvida pelo tecido quando submetido à radiação. Este efeito ocorre devido aos fotoelétrons ejetados do material de alto número atômico. Dosímetros de gel polimérico com partículas de ouro foram utilizados para investigar este efeito. Foram realizados cálculos analíticos para estimar o aumento de dose e simulações com o método de Monte Carlo. A irradiação de amostras de gel polimérico (GP) puro e com 0,005 gAu/gGP utilizando um feixe de raios X produzido por um potencial de 150 kV filtrado com 4 mmAl e 5 mmCu resultou em uma dose absorvida pelas amostras com ouro aproximadamente 20% maior que a dose absorvida pelas amostras de gel polimérico puro. Os cálculos analíticos e a simulação com o método de Monte Carlo resultaram em um aumento de aproximadamente 30% na dose absorvida. / The presence of high-Z material adjacent to soft tissue, when submitted to irradiation, enhances locally the absorbed dose in these soft tissues. Such effect occurs due to the outscattering of photoelectrons from the high-Z material. Polymer gel dosimeters have been used to investigate this effect. Analytic calculations to estimate the dose enhancement and Monte Carlo simulations have been performed. Samples containing polymer gel (PG) with 0.005 gAu/gPG and pure polymer gel have been irradiated using an X-rays beam produced by 150 kV, filtered with 4 mm Al and 5 mm Cu, which resulted in an approximately 20% higher absorbed dose in the samples with gold in comparison to those with pure polymer gel. The analytic calculations and the Monte Carlo simulation resulted in a dose enhancement factor of approximately 30%.

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

Este trabalho visa aprimorar e tornar mais precisa a utilização do dosímetro gel polimérico MAGIC-f no estudo da distribuição de dose para fonte radioativas utilizadas na terapia e diagnóstico em medicina nuclear. Para isso foram avaliados os parâmetros de leitura do gel em equipamentos de ressonância magnética e sua resposta quando comparado a resultados obtidos através da utilização do código PENELOPE de simulação Monte Carlo. Dentre as incertezas observadas no processo global da utilização do gel MAGIC-f, sua manufatura foi a que demonstrou uma maior preocupação uma vez que erro na frações de componentes químicos adicionados ocasiona grande diferença na resposta do dosímetro. A aquisição da informação dosimétrica em um equipamento de imagem por ressonância magnética demonstrou que tempos ao eco mais curtos são mais eficientes na diferenciação do sinal gerado no processo de polimerização devido a utilização de fontes de medicina nuclear do que ajustes na resolução da imagem e que a homogeneidade de campo magnético pode ocasionar grande alteração nos valores obtidos. Experimentos realizados com o gel MAGIC-f, demonstraram um baixa dependência energética e um grande dependência com a taxa de dose, dois fatores importantes em medicina, mas resultados simulados e experimentais comparativos utilizando fontes de I-131, Tc-99m e F-18, demonstraram uma grande precisão nos resultados apresentados, tornando assim o gel MAGIC-f uma excelente ferramenta na verificação volumétrica da dose absorvida na terapia com fontes de medicina nuclear. / This work aims to improve and make more accurate use of the gel dosimeter MAGIC-f polymer in the study of dose distribution for radioactive source used in therapy and diagnosis in nuclear medicine. For this, MRI parameters reading of the gel were evaluated and its response when compared to results obtained using a Monte Carlo simulation PENELOPE code. Among the uncertainties observed in the overall use of MAGIC-f gel, its manufacturing demonstrated a greater concern since error in chemical fractions added causes big difference in the response of the dosimeter. The acquisition of dosimetric equipment information in a magnetic resonance imaging showed that the shorter eco times are more efficient in differentiating the signal generated in the polymerization process due to the use of sources of nuclear medicine than image resolution changes and the homogeneity of the magnetic field can cause large difference in the results. Experiments performed with the MAGIC-f gel, demonstrated a low energy dependence and a large dependence on the dose rate, two important factors in nuclear medicine, but comparative results with simulated and experimental processes using sources of I-131, Tc-99m and F-18 showed a great accuracy in results, thus making the MAGIC-f gel an excellent tool for volumetric verification of absorbed dose therapy with sources of nuclear medicine.

New radiation therapy (RT) techniques for treating cancer are continually under development. Our ability to demonstrate the safe and accurate implementation of new RT treatment techniques is dependent on the information provided by current dosimetric tools. Advanced dosimetric tools will become increasingly necessary as treatments become more complex. This work examines the readout of an advanced dosimeter --- the polyacrylamide, gelatin, and tetrakis (hydroxymethyl) phosphonium chloride (PAGAT) dosimeter --- using a prototype fan-beam optical computed tomography (CT) scanner. A number of developments sought to improve the performance of the optical CT device. A new fan-creation method (laser diode module) and new matching tank were introduced. Artefact removal techniques were developed to remove flask seam artefacts and ring artefacts via sinogram space. A flask registration technique was established to achieve reproducible placement of flasks in the optical CT scanner. A timing-correction technique was implemented to allow for the scanning of continuously rotating samples. A number of experiments examined factors related to the PAGAT dosimeter. Comparisons of post-irradiation scans to pre-irradiation scans improved dosimeter readout quality. Changes to the PAGAT dosimeter cooling/scanning routine provided further improvements to dosimeter readout. Evaluations of calibration curves showed that a linear calibration curve was less capable of describing PAGAT dose response than a quadratic calibration curve. Intra-gel calibration using another dose distribution was shown to be no less accurate than self calibration, but inter-gel calibrations saw a statistically significant increase in absolute readout errors. A set of investigations examined how optical CT scanning protocols affected readout quality for PAGAT dosimeters. Doubling the dose delivered to the dosimeter doubled the signal-to-noise ratio. Acquiring and averaging additional light profiles at each projection angle provided only slight reductions in readout noise. Sampling a higher number of projection angles provided substantial reductions in readout noise. Those reductions in readout noise were not lost when sinograms with many projections were encapsulated into sinograms of fewer projection angles. Detector element binning (sinogram space) and pixel binning (image space) also provided substantial reductions in readout noise. None of these elements of the scanning protocol had statistically significant effects on readout errors. Finally, distinct imaging artefacts seen throughout this work were shown to be caused by radiation-induced refractive index changes in PAGAT dosimeters. Radiation-induced refraction (RIR) artefacts result when dose gradients caused the refraction of fan-beam raylines towards high dose regions. A filtering technique was developed to remove RIR artefacts in sinogram space, but this technique caused substantial blurring to the measured dose distribution. / Graduate / 0760 / 0756 / 0752 / warreng1983@gmail.com

Des membranes polymères catalytiques ont été préparées via la polymérisation photo-amorcée de monomères acryliques à la surface de membranes support MicroPES(r). Des nanoparticules de palladium (PdNP) avec diamètre moyen compris entre 4 et 10 nm sont ensuite synthétisés et immobilisées dans ces gels polymères greffés. Cette thèse se focalise sur le greffage d'un gel de polymère neutre : (2-hydroxyethyl acrylate) (PHEA), pour négliger les contributions ioniques du réseau polymère sur la synthèse in-situ des PdNP. La stabilisation de PdNP dans le gel de PHEA greffé est possible par des moyens stériques étant donné que la distance entre des chaînes de polymère réticules (entre 0.3 à 2.5 nm) est plus petite que le diamètre moyen de PdNP. Une approche à la fois théorique et expérimentale, sur la base des mecanismes de nucléation et de croissance, permet la conception de PdNP de taille spécifique. La performance catalytique des membranes a été évaluée avec une configuration en filtration traversée. Sur la réaction de couplage de Suzuki-Miyaura, des conversions et sélectivités de 100 % ont été obtenues pour des temps de séjour de 10 secondes avec des membranes planes. Les réactions d'hydrogénation de plusieurs composés aromatiques ont également été testées. Des taux de conversion élevés ont été obtenus en quelques secondes avec des membranes planes en filtration avec des solutions saturés d'H2. Des taux de conversion élevés sont obtenus en seulement quelques minutes avec des membranes fibres creuses catalytiques en mode contacteur permettant une importante intensification du procédé. / Catalytic polymeric membranes are prepared via photo-grafting polymerization of neutral acrylic monomers onto the surface of a MicroPES(r) membrane support. Palladium nanoparticles (PdNP) of mean diameter of 4-10 nm are synthetized and immobilized within the grafted polymer gels. The research is focused on grafting a neutral polymer gel: poly (2-hydroxyethyl acrylate) (PHEA), to avoid any ionic contribution of the polymer network on the in-situ synthesis of PdNP. The stabilization of PdNP within the grafted PHEA is achieved by steric means as the distance between polymeric crosslinked chains (ca. 0.3 to 2.5 nm) is smaller than the mean diameter of PdNP. Both theoretical and experimental approaches are presented on the PdNP synthesis as an approach to conceive PdNP of specific sizes using nucleation and growth theories. Catalytic performance of the membranes is evaluated in flow-through configuration. Catalytic tests are performed on Suzuki-Miyaura cross-coupling reactions. Full conversion and selectivity within 10 seconds of residence time using flat sheet membrane are obtained. Hydrogenation of several aromatic compounds are also tested and high conversions were achieved within seconds of residence time using flat sheet membranes in flow-through configuration with H2-saturated solutions and within minutes using catalytic hollow fibers in contactor mode.

Doubly cross-linked gels were fabricated based on tetra-poly(ethylene glycol) (Tetra-PEG) by shear strain. These are gels with two network structures present in the same polymeric network. The second network structure is introduced by applying a mechanical field to the first natural network structure. These doubly cross-linked gels indicated a negative energy elasticity supporting earlier findings where the energy elasticity was found significantly negative for Tetra-PEG gel. Acquired results indicate implications for past research on the elasticity of polymer gels where the energy contribution was approximated to zero. Obtained results also indicated that the modulus of rigidity for the doubly cross-linked gels is constant regardless of applied shear strain during fabrication. This would indicate that the same second network structure is formed for the interval of 25-800% applied shear strain. The residual strain for the fabricated gels can be well-described using an exponential fitting of the apparent shear modulus of the first network structure and an expression derived from the two-network theory and classic rubber theory. These theories also seem to predict the experimental residual strains for lower strain regions (<100%) quite well. However for larger strain regions (>100%) non-linear effects seem to affect the results causing a deviation. A slight increased modulus of rigidity was noted for the doubly cross-linked gels compared to the regular Tetra-PEG gel. However as the reproducibility of the concluded measurements could not be confirmed during this thesis the results are not conclusive and only indicate the conclusions mentioned above.

Der moderne Entwicklungsprozess von Bauteilen umfasst nicht nur Aspekte der funktionsgerechten Dimensionierung, sondern berücksichtigt auch Materialien, die auf Umgebungsbedingungen reagieren oder deren Verhalten sich von außen regeln lassen kann. Im Allgemeinen weisen diese Materialien mechanische Eigenschaften auf, die von mindestens einem weiteren physikalischen Feld, das zum Beispiel elektrischer, magnetischer oder chemischer Natur sein kann, aufgrund dem Material eigener innerer Wechselwirkungen beeinflusst werden. In der Literatur wird für diese Klasse von Materialien häufig der Begriff smart materials oder intelligent materials verwendet [Leo07]. Für die Forschung stellten diese Materialien in den letzten Jahren ein außerordentlich spannendes Aufgabenfeld dar, sodass eine Vielzahl von Materialien klassifiziert werden konnte [BC04] und auf Basis ihrer charakteristischen Eigenschaften neuartige Sensor- und Aktorsysteme entstanden sind [GA10]. Ein Beispiel ist das in Abbildung 1.1 dargestellte Modell eines Chemosensors auf Basis eines polyelektrolyten Gels, der am Institut für Festkörperelektronik der TU Dresden entwickelt wurde.

Dans cette thèse, une solution de caoutchouc de styrène-butadiène (SBR) réticulé avec du peroxyde organique, a été transformé en un gel autodégradable par l’ajout d’hydropéroxyde comme agent de dégradation. La formulation a été caractérisée en rhéologie dynamique. Les spectres de temps de relaxation ont été calculés à partir des modules dynamiques de cisaillement, par une nouvelle méthode développée dans ces travaux présentée avec une revue complète de méthodes pour le calcul des spectres de relaxation à partir de données de rhéométrie de cisaillement. Des expériences in-situ et ex-situ ont été réalisées afin d’évaluer l’évolution de les réactions de réticulation et dégradation. Les changements de la structure du réseau polymérique sont mises en évidence dans les spectres de temps de relaxation. La cinétique de la dégradation de la solution de SBR a été étudiée dans des conditions anaérobies et caractérisée par diffusion de la lumière multi-angles couplée à la chromatographie d’exclusion stérique (SEC-MALS). En utilisant des équations de bilan de populations, nous avons pu calculer les constantes cinétiques de dégradation thermique et thermo-oxydative. Différentes formulations de ces gels auto-dégradables à base d’huile ont été évaluées en tant que potentiels agents de dérivation pour des opérations de traitement de puits. Le comportement rhéologique de ces gels a été mesuré en fonction du temps, pour vérifier la réticulation du polymère, la force de gel, et la dégradation ; ces variables peuvent être ajustées aux nécessités de l’opération de traitement en jouant sur la formulation. Des tests d’écoulement dans carotte simples ont été réalisés pour évaluer la résistance à la pression en fonction de la force du gel et de sa dégradation. Des tests d’écoulement dans carottes parallèles ont également été menés, afin d’évaluer l’efficacité de la dérivation et la restauration de mobilité. / In this work, a solution of peroxide crosslinked styrene-butadiene rubber (SBR) has been transformed to a self-degradable gel system by adding hydroperoxide as a degradation agent to the formulation. Dynamic rheometry was employed to calculate the relaxation time with a new method presented along with a full review of methods for calculation of the relaxation time spectrum from oscillatory rheometry. In-situ and ex-situ experiments were performed to evaluate the evolution of crosslinking and degradation reactions. Structural changes in the polymer network were visible within the relaxation time spectra. The degradation kinetics of styrene butadiene rubber (SBR) in solution was studied in anaerobic conditions and the characterization was performed by multiangle light scattering coupled to size exclusion chromatography (SEC-MALS). Using population balance equations, it was possible to calculate the kinetic constants for thermal and thermooxidative degradation. Different formulations of these oil-based self-degradable gels have been evaluated as possible diverting agents during oil wells operations. The time dependent rheological behavior of the gels was measured to verify polymer crosslinking, maximum gel strength and gel degradation, all of which can be adjusted by varying formulation depending on operation needs. Single core tests were performed to evaluate pressure resistance as a function of gel strength and gel degradation. Parallel cores tests were also carried out to validate diversion efficiency and mobility restoration.

A dynamic mathematical model was developed to simulate the response of polyacrylamide gel (PAG) dosimeters to a single spherical radioactive brachytherapy seed. Simulations were conducted for a high dose-rate (HDR) seed using 192Ir and a low dose-rate (LDR) seed using 125I. The model is able to predict the amount of polymer formed, the crosslink density, and the volume fraction of aqueous phase as a function of radial distance and time. Results show that PAG dosimeters can provide accurate HDR brachytherapy dosimetry at distances larger than 4 mm from the centre of the seed but will give poor results for LDR due to monomer diffusion. Experiments were conducted to evaluate the potential for using pentacosa-10,12-diynoic acid (PCDA) as the reporter molecule in micelle gel dosimeters for optical computed tomography (CT) readout. Several gels containing PCDA that was solubilized using sodium dodecyl sulfate (SDS) responded to radiation by changing from colourless to blue. Unfortunately, all phantoms that showed colour changes were turbid, making them unsuitable for optical CT scanning. Several techniques were used to produce transparent gels containing PCDA but none of these gels responded noticeably to radiation. Only turbid gels with precipitated PCDA responded, indicating that the colour change was due to oligomerization within PCDA crystals and that PCDA molecules solubilized in micelles did not undergo oligomerization. As a result, PCDA is not suitable for use in radiochromic micelle gel dosimeters. A new recipe for a radiochromic leuco crystal violet (LCV) micelle gel dosimeters with enhanced dose sensitivity was developed for optical CT readout. The recipe contains LCV, trichloro acetic acid (TCAA), Cetyl Trimethyl Ammonium Bromide (CTAB), 2,2,2-Trichloroethanol (TCE), and gelatin. Experiments were conducted to improve understanding about interactions between the different components of LCV micelle gel, highlighting the importance of pH on dose sensitivity and transparency. Results also showed the effectiveness of chlorinated compounds in improving dose sensitivity. Statistical techniques were used to build empirical models that were used to optimize the gel recipe. Additional testing in larger phantoms will be required to assess the effectiveness of the proposed gel for clinical dosimetry. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2014-03-27 11:11:47.655