Dissertations / Theses on the topic 'TLD dosimeter'

Os órgãos de saúde internacionais e nacionais, como o Ministério da Saúde na portaria 453/98 da Vigilância Sanitária, exigem que a Dose de Entrada na Pele seja avaliada para cada equipamento mamográfico através da leitura de um sistema câmara de ionização-eletrómetro corrigida pelo fator de retroespalhamento. Ao não existir menção explícita na portaría de valores utilizáveis para o fator de retroespalhamento, este trabalho visa à determinação experimental do fator de retroespalhamento, através da utilização dos dosímetros termoluminescentes TLD-100. No estudo são verificadas as dependências geométricas e espectrais do fator de retroespalhamento, assim como do valor da Dose de Entrada na Pele, e da Dose em Profundidade, correspondentes com as técnicas radiográficas empregadas nos exames mamográficos convencionais de rotina. Foram avaliados feixes na faixa de 0,35 mmAl até 0,43 mmAl, tensões do tubo de 25kV, 28kV, 30kV, e 32kV, assim como os três tamanhos de campo disponíveis no Mamógrafo Senographe DMR utilizado, e distancias focofilme iguais a 56cm, 61cm e 66cm. Os resultados obtidos foram comparados com publicações existentes, as quais apresentam resultados obtidos através de Simulação Monte Carlo, câmaras de ionização, e dosímetros TLD-100. Os resultados obtidos neste trabalho permitem estabelecer e discutir as dependências das grandezas dosimétricas estudadas com a Camada Semi-Redutora, tensão do tubo, combinação ânodo-filtro, tamanho de campo, distância foco-filme e espessura da mama.
National and international health organizations such as the Brazilian Ministry of Health, through its Secretary of Health Surveillance establishes in the publication Nº 453/98 that in all mammographic equipments must be evaluated the entrance-skin dose through the readings of an ionization chamber-electrometer system corrected by the backscatter factor, among others factors. Nevertheless, there is no explicit mention for useful values of backscatter factor in this document; the main aim of this work is the experimental determination of backscatter factor through the use of TLD-100 dosimeters. In this study, the geometric and spectral dependencies of the backscatter factor, entrance-skin dose and the in-depth dose were evaluated, corresponding to the most radiographic techniques employed in conventional mammographic procedures, i.e., beam qualities in the range of 0.35 mmAl to 0.43 mmAl, tube voltages from 25kV to 32kV, focus-film distances from 56cm to 66cm, and three field sizes were evaluated. Our results were compared with those previously published obtained through Monte Carlo simulation, ionization chambers and TLD dosimeters. The results obtained in this work allow studying the dependency of the mentioned dosimetric quantities with the half-value layer, tube voltage, anode-filter combination, field size, focusfilm distance and breasting thickness of the breast.

Many radiation detection programs use bio-assays, whole-body counters, or air sampling to estimate internal doses. This study examines the possibility of using a common external thermoluminescent dosimeter (TLD) badge as a device for detecting inhaled radionuclides through radiation those radionuclides emit which escape the body. The three common radionuclides chosen for modeling due to their varying decay modes and use or production in the nuclear industry were Cs-137, U-238, and Sr-90. These three radionuclides were modeled for biological and radiological removal in the dynamic systems modeling program of STELLA II and modeled for TLD dose per organ in the geometry and radiation simulation program of MCNP. The results show that none of the nuclides in the study can be detected at air concentrations below regulatory limits for acute inhalation exposures. To achieve a detectable dose from an 8-hour work exposure, with a 90-day wait until the TLD is read, the airborne concentrations for the inhalation classes that produced the most dose per Bq would be 37.9 kBq/m3, 146 MBq/m3, and 1.67 MBq/m3 for Cs-137, U-238, and Sr-90, respectively.

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.

A Terapia por Captura de Nêutrons, NCT (Neutron Capture Therapy) é uma técnica radioterápica em que a energia útil do tratamento vem da energia liberada em uma reação nuclear e não do feixe primário, como comumente utilizado em outros procedimentos radioterápicos. O Boro, por constituir-se em um elemento de baixa toxicidade e por apresentar um isótopo (10B) com alta seção de choque para a reação 10B(n,α)7Li tem sido o elemento mais utilizado nas pesquisas que visam o aprimoramento e a promoção desta técnica, derivando daí o termo BNCT (Boron Neutron Capture Therapy). Para fins de pesquisa em BNCT foi construída ao longo de um dos extratores de feixes (BH - Beam Hole) do reator IEA-R1 uma instalação, onde filtros e moderadores são posicionados entre o núcleo do reator e a posição de irradiação com o objetivo de modular o feixe de irradiação, otimizando a componente útil do feixe, os nêutrons térmicos, e reduzindo os contaminantes, raios gama e nêutrons em outras faixas energéticas. Tem-se realizado estudos visando a implementação de melhorias na caracterização e otimização do feixe obtido nesse arranjo instalado no BH-3. Atualmente a monitoração dos nêutrons é feita através de folhas de ativação, e a componente gama pelo TLD-400. Uma nova metodologia de monitoração tem sido estudada pelo grupo. A referida técnica consiste em usar TLDs de tipos diferentes, ou seja, que possuam sensibilidades distintas aos nêutrons térmicos, em virtude de diferenças na concentração dos isótopos de Lítio. No estudo dessa nova metodologia têm sido usados os TLD-600 e TLD-700. Este trabalho propõe uma metodologia usando o par TLD-100 e TLD-700. Inicialmente foi verificada a reprodutibilidade das respostas dos TLDs 700, 400 e 100 frente a campos gama puro e campos mistos, gama e nêutron. Campos estes obtidos em arranjos usando fontes de 60Co e 241AmBe. A partir de simulações usando o VI MCNP5 foi projetado e construído um Irradiador de campos mistos, que permitiu expor os dosímetros em campos mistos com diferentes espectros energéticos. As condições criadas no irradiador permitiram verificar, como a resposta do TLD é modificada pelas mudanças no espectro energético de um campo misto gama e nêutrons de baixo fluxo. O irradiador de campo misto permitiu condições para estabelecer uma relação entre o formato da curva termoluminescente e a composição do campo misto. A relação estabelecida relaciona o fluxo relativo e a razão entre a resposta das duas regiões de interesse dos TLDs 700 e 100. A partir de campos mistos com condições controladas, esse trabalho permitiu verificar a viabilidade do uso do par de TLD-100 e TLD-700 para monitoração de nêutrons térmicos na instalação de BNCT.
Neutron Capture Therapy (NCT), is a radiotherapy technique in which the useful treatment energy comes from the energy released in a nuclear reaction and not from the primary beam, as commonly used in other radiotherapc procedures. Boron, an element of low toxicity presents an isotope (10B) with high cross-section for the (n, α) reaction and therefore has been the element mostly used in research aimed at the improvement and promotion of this technique, deriving hence the term BNCT (Boron Neutron Capture Therapy). For BNCT research purposes, a facility was built along one of radiation extractors of the IEA-R1 reactor. In this facility filters and moderators are positioned between the reactor core and the irradiation position aiming to modulate the irradiation beam by optimizing the useful component of the beam, thermal neutrons, and reducing its contaminants, gamma rays and neutrons in higher energy bands. We have conducted studies aimed at implementing improvements in the characterization of and optimization of the beam. Currently, neutron flux monitorion is done through activation foils, and the gamma component by TLD-400. A new methodology has been studied by the group. The technique consists in using different types of TLD, having different sensitivities to thermal neutrons due to differences in the concentration of lithium isotopes. In the study of this new methodology TLD 600 and TLD-700 have been used. This work presents a series of studies in order to apply a methodology using the TLD-100 and TLD-700 pair. TLDs 700, 400 and 100 responses pure gamma and mixed irradiation fields, obtained in arrangements using a 60Co and AmBe sources, were evaluaterd. MCNP simulations were run in order to both discriminating the radiation components and designing one mixed fields irradiator, which allowed exposing dosimeters in mixed fields with different energy spectra. The conditions created in the irradiator allowed to verify, as the TLD response is modified by changes in the energy spectrum of a mixed gamma neutron fields. VIII This irradiator provided irradiation conditions so to establish a relationship between the shape of the LiF glow curves and the composition of the mixed field. This work has shown the feasibility of using the TLD-100 and TLD-700 pair for gamma and thermal neutrons monitoration in the BNCT facility.

A dosimetria in vivo é a verificação final da dose real administrada ao paciente e tornou-se atualmente necessária devido ao aumento da complexidade e da sofisticaçã das técnicas radioterápicas. A finalidade deste trabalho foi apresentar, verificar e avaliar alguns procedimentos básicos, práticos e viáveis para a implementação da dosimetria in vivo com dosímetros termoluminescentes na verificação de dose em um serviço de radioterapia. Para o estabelecimento do sistema dosimétrico termoluminescente, alguns testes e medições foram realizados, incluindo o procedimento de inicialização, a determinação da homogeneidade do grupo de dosímetros, a determinação do fator de correção individual de cada dosímetro, a determinação da faixa de linearidade do sistema e do coeficiente de calibração. Medições em um objeto simulador antropomórfico foram realizadas para garantir que os métodos utilizados são satisfatórios antes que estes fossem usados para medições em pacientes. Medições de dose em um paciente foram feitas em um tratamento de câncer de próstata. A metodologia proposta pode ser usada como parte de um programa de garantia de qualidade em um serviço de radioterapia.
In vivo dosimetry is the ultimate check of the actual dose delivered to an individual patient and has become a procedure actually necessary due to increasing complexity and sophistication of radiotherapy techniques. The purpose of the present work was to present, verify and evaluate some basic, practical and viable procedures for the implementation of in vivo dosimetry with thermoluminescent dosimeters for patient dose verification at a radiotherapy service. For the setting up of the thermoluminescent dosimetric system, several tests and measurements were carried out including the initialisation procedure, the determination of the batch homogeneity, the determination of individual correction factor of each dosimeter, the determination of linearity range of the system and its calibration coefficients. Anthropomorphic phantom measurements were taken to ensure that the methods are satisfactory before they are used for patients measurements. Patient dose measurements were carried out in a prostate cancer treatment. The proposed methodology can be used as a part of a quality assurance program in a radiotherapy service.

A Terapia de Captura de Nêutron por Boro (BNCT) é uma terapia de combate ao câncer bimodal, na qual a energia útil da terapia vem da reação nuclear que ocorre pelo Boro quando irradiado com nêutrons térmicos. No IPEN há uma instalação de pesquisas em BNCT, na qual o feixe de radiação contendo nêutrons é proveniente do reator IEA-R1. Como condição desta terapia é necessário realizar a dosimetria do feixe de radiação, que atualmente é feito com o uso de folhas de ativação, para cálculo do fluxo de nêutrons, e do dosímetro TLD 400, para estimativa da dose gama. Para campos mistos de nêutrons e gamas, a Comissão Internacional de Unidades e Medidas (ICRU) recomenda o uso de dosímetros com sensibilidades distintas para as componentes do feixe, como o caso do par TLD 600 e TLD 700 que apresentam sensibilidades distintas a nêutrons térmicos, devido à diferente quantidade do isótopo 6Li em sua composição, o qual apresenta uma alta seção de choque para nêutrons térmicos. Este trabalho constou da realização de simulações e experimentos visando a implementação da metodologia de dosimetria utilizando o par TLD 600 e TLD 700 e sua comparação com a metodologia atualmente utilizada pelo grupo de pesquisa em BNCT, que utiliza o TLD 400. Portanto, foi realizado um estudo das respostas de cada um destes TLDs a partir de irradiações em diferentes campos e sempre utilizando simulações com o MCNP para fornecer a discriminalização das componentes de dose depositadas em cada TLD. Foram realizadas varias irradiações em campo de gama puro e em campo misto de nêutrons e gamas para o estudo da reprodutibilidade destes TLDs. Este estudo mostrou que mesmo TLDs do mesmo tipo têm sensibilidades distintas, e assim foi criado um Fator de Normalização para cada um dos TLDs, eliminando assim a necessidade de selecionamento. Foi realizado um estudo sobre a diferença das respostas destes TLDs devido à diferentes campos. Este estudo mostrou ser possível estimar o fluxo relativo entre gamas e nêutrons a partir da relação existente entre as duas regiões de interesse dos TLDs 600 e 700. Também foi possível observar que o TLD 700 apresenta resposta para nêutrons, e se a recomendação da ICRU for seguida, a resposta devido à radiação gama será superestimada. Foram obtidas as curvas de calibração dose resposta destes TLDs para campos de gamas puro e campos mistos. Este trabalho propõe o uso desta metodologia com o uso do par TLD 600 e TLD 700, por apresentar maior precisão de resposta frente a atual metodologia que utiliza o TLD 400, porém precauções devem ser tomadas para evitar que a dose gama seja superestimada.
Boron Neutron Capture Therapy, BNCT, is a bimodal radiotherapic procedure for cancer treatment. Its usefull energy comes from a nuclear reaction driven by impinging thermal neutron upon Boron 10 atoms. A BNCT research facility has been constructed in IPEN at the IEA-R1 reactor, to develop studies in this area. One of its prime experimental parameter is the beam dosimetry which is nowadays made by using activation foils, for neutron measurements, and TLD 400, for gamma dosimetry. For mixed field dosimetry, the International Commmission on Radiation Units and Measuments, ICRU, recommends the use of pair of detectors with distinct responses to the field components. The TLD 600/ TLD 700 pair meets this criteria, as the amount of 6Li, a nuclide with high thermal neutron cross section, greatily differs in their composition. This work presents a series of experiments and simulations performed in order to implement the mixed field dosimetry based on the use of TLD 600/TLD 700 pair. It also intended to compare this mixed field dosimetric methodology to the one so far used by the BNCT research group of IPEN. The response of all TLDs were studied under irradiations in different irradiation fields and simulations, underwent by MCNP, were run in order to evaluate the dose contribution from each field component. Series of repeated irradiations under pure gamma field and mixed field neutron/gamma field showed differences in the TLD individual responses which led to the adoption of a Normalization Factor. From the use of Normalization Factor the TLD selection it has allowed to overcome TLD selection. TLD responses due to different field components and spectra were studied. It has shown to be possible to evaluate the ralative gamma/neutron fluxes from the relative responses observed in the two Regions of Interest of TLDs glow curves, ROIs, from TLD 600 and TLD 700. It has also been possible to observe the TLD 700 response to neutron, which leads to a gamma dose overstimation when one follows the ICRU recommended mixed field dosimetric procedure. Dose response curves were obtained for the distinct types of TLDs for pure gamma and mixed fields. This work recommends the TLD 600/TLD 700 pair methodology for mixed field dosimetry, this methodology presents a better precision than the one based on TLD 400, however one has to be carefull to avoid gamma dose superestimation.

Background: In an ongoing study conducted at Karolinska Institutet & Karolinska University Hospital, Positron Emission Tomography (PET)/Computed Tomography (CT) scans are performed on patients with tibia fractures and deformations treated with Taylor Spatial Frames (TSFs) in order to monitor their bone remodeling progress. Each patients receive an administration of approximately 2 MBq/kg bodyweight of Na18F associated with PET scans on two sessions, six and twelve weeks after the attachment of the TSF. These PET/CT scans provide information about the progress of the healing bone and can be used to estimate the optimal time point for de-attachment of the TSF. The Standardized Uptake Value (SUV) is used as a measure of the rate of bone remodeling for these patients, however, there is a need for verification of this practice by a method independent of the PET scanner. Furthermore, information regarding the biodistribution of the Na18F throughout the body of these patients and the effects of the TSF on the CT scan X‑rays is required. Additionally, an investigation of alternative methods that have the potential to provide similar information with a lower absorbed dose to the patients is desirable. Materials and methods: Thermoluminescent Dosimeters (TLDs) were attached on the skin at the position of the heart, urinary bladder, femurs, fracture, and the contralateral tibia of twelve patients during the first one hour and five minutes after the administration of the Na18F. Additional TLD measurements were performed during the CT scan of two of these patients. From the PET scan images, SUVs at the fracture site of these patients were collected. An investigation of the possibility of exploiting the “naturally” occurring bone seeking radionuclide Strontium-90 (90Sr) in the human body to gain information about the fracture site was undertaken. Using a 90Sr source, three different detection techniques were evaluated and a practical methodology for in vivo measurements on the tibia fracture patients was developed. As it was concluded that TLD based measurements were the most suitable technique for this purpose, and it was tested on five patients with tibia fractures. Results: From the collected TLD data, it was concluded that for these patients the urinary bladder is the organ receiving the greatest amount of absorbed dose and the organ most affected as the administered activity exceeds 2 MBq/kg. On average, a three times higher surface dose was measured on the tibia fracture compared to the un-fractured tibia. A linear relationship between the surface dose and SUVmax was shown. A strong positive correlation between the activity concentration at the fracture site and the amount of injected activity was found, and it was demonstrated that this also affects the SUVs. For patients who were administered different amounts of Na18F for the two PET scans, maximum activity concentrationwas less affected than mean activity concentration. It was concluded that TSF’s effect on the scatter of the X-rays to organs higher up in the body is negligible. Regarding “naturally” occurring 90Sr in the human body, no higher activity at the fractured tibia compared to the non‑fractured tibia could be found. Conclusions: This project assessed the accumulation of Na18F in the fracture site of patients treated with TSF by a method independent of the PET scanner. The methodology of using SUVs as an indicator for bone remodeling was verified. It was shown that the uptake of Na18F by the fracture site is strongly correlated to the amount of injected activity. The importance of considering the amount of injected activity when evaluating and comparing SUVs was highlighted. In vivo measurements using LiF:Mn TLDs did not indicate any quantifiable higher concentration of 90Sr at the fracture in the tibia bone.

Depuis plusieurs années, le développement des technologies sans fil utilisant les ondes électromagnétiques dans différents milieux d’applications (télécommunications, médicales, militaires) ne cesse d’augmenter. Il devient donc nécessaire d’évaluer les effets de l’environnement sur les antennes en amont de leur conception afin d’optimiser la transmission entre les divers objets connectés. De plus, les études sur les systèmes utilisant les ondes électromagnétiques amènent à se poser un certain nombre de questions autour de l’interaction ondes/vivant, nous obligeant à considérer des modèles fortement hétérogènes tel que le corps humain.Face aux difficultés de mesures, la simulation permet de quantifier numériquement la puissance absorbée par les tissus au travers du DAS et l’élévation de la température correspondante. Dans ce domaine, la méthode TLM (Transmission Line Matrix) s’est révélée être particulièrement adaptée au calcul du DAS dans des structures fortement hétérogènes grâce à la colocalisation des champs au centre de la maille.Au cours de cette thèse, un outil basé sur la méthode TLM permettant d’effectuer des études dosimétriques en calculant le DAS et la température dans des milieux fortement hétérogènes a été développé. La première étape a été consacrée au développement d’un « module »pour calculer la DAS et la mise en place d’une interface pour lire les modèles voxélisés. Ensuite, un solveur thermique basé sur la TLM a été développé afin de simuler la température dans des milieux biologiques exposés aux ondes EM. Enfin, la comparaison avec le logiciel commercial CST a permis de valider notre outil et de l’appliquer par la suite pour étudier l’exposition d’une tête humaine au rayonnement d’un Smartphone modélisé par une PIFA fonctionnant à 900MHz
For several years, the development of the wireless technologies using the electromagnetic waves in various applications (telecommunications, medical, military …) does not stop increasing. Thus, it becomes necessary to evaluate the effects of the environment on antennas upstream to their conception to optimize the transmission between diverse connected objects. Furthermore, studies on the systems using the electromagnetic waves lead to ask a number of questions about waves/living interaction, obliging us to consider highly heterogeneous models such as human body.In front of difficulties of measures, the simulation allows to quantify numerically the power absorbed by tissues and the corresponding temperature rise. In this domain, the TLM method (Transmission Line Matrix) has proved to be particularly adapted to the simulation of the SAR in highly heterogeneous structures thanks to the co-localisation of the fields at the centre of mesh.In this thesis, a tool based on the TLM method to make dosimetrics studies by calculating the SAR and the temperature in highly heterogeneous media has been developed. The first step was dedicated to the development of a “module” to calculate the SAR and the implementation of an interface to read the voxelized models. Then, a thermal solver based on the TLM was developed in order to simulate the temperature in biological media exposed to the EM waves. Finally, the comparison with the commercial software CST allowed to validate our tool and to apply it afterward to study the exposure of a human head to the radiation of a Smartphone modelled by a PIFA antenna operating at 900MHz

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

A Terapia Fotodinâmica (TFD) é uma técnica que provoca dano celular pela ação de um fotossensibilizador (FS), com seletividade de localização em tecido tumoral; a luz que, absorvida pelo FS, leva-o a um estado tripleto metaestável; e oxigênio molecular, o qual recebe a energia absorvida pelo FS, passando a um estado singleto de alta capacidade oxidativa. A técnica é bem sucedida no tratamento de lesões como câncer, mas enfrenta, entretanto, dificuldades para a determinação de sua dosimetria. Uma delas é a quantificação da distribuição do FS no tecido tratado. Este trabalho tem três objetivos: a obtenção de informação quantitativa por espectros de fluorescência de fluoróforos em meios turvos; a demonstração da distribuição do FS Photogem® em fígados sadios de ratos Wistar e suas implicações na dosimetria; e a melhoria de um dos modelos existentes para previsão da profundidade de necrose (Ynec), importante parâmetro no estudo da TFD. Realizaram-se os experimentos em três fases: na primeira, tentou-se reconstruir o espectro do fígado sadio a partir de uma composição de espectros isolados de fluoróforos endógenos do fígado. Na segunda, realizaram-se estudos com corantes alimentícios Coralim-Mix® nas cores azul, verde e vermelho e com corantes Exciton® (Coumarin-480 e LDS-722) in vitro e in vivo, visando identificar os espectros dos corantes em misturas com meios turvos e entre eles. Na terceira, aplicou-se Photogem® em ratos Wistar e se coletou a fluorescência do FS nos fígados, relacionando-se a variação na intensidade de fluorescência com a concentração de FS presente e com perfis de necrose obtidos por TFD. Aplicou-se, por fim, os resultados obtidos na melhoria do modelo para previsão da Ynec. A reconstrução dos espectros não foi bem sucedida, tal qual a recuperação dos espectros dos corantes. Os resultados mostraram que muitos fatores contribuem para a distorção da fluorescência coletada, e que a informação obtida é prejudicada se estes forem ignorados. Verificou-se que a distribuição do FS não é homogênea num órgão fotossensibilizado. Obteve-se uma função para distribuição do FS no tecido e, através dela, foi possível melhorar o modelo para a previsão da Ynec. Observou-se que a turbidez do meio afeta de maneira complexa a coleta de fluorescência, criando obstáculos para a quantificação direta de fluoróforos nele inseridos. Fica evidente a necessidade do aprofundamento dos estudos sobre a interação da luz com as partículas dos meios turvos para remover as distorções geradas por estas. Demonstrou-se ainda a importância do mapeamento da distribuição do FS num tecido fotossensibilizado como parte da dosimetria da TFD, e que a espectroscopia de fluorescência é forte candidata à técnica mais apropriada para este mapeamento, desde que dominados os obstáculos à coleta de fluorescência.
Photodynamic Therapy (PDT) is a technique that implies in cell damage by the action of a photosensitizer (PS) with tumor tissue localization selectivity; light at PS absorption spectrum wavelengths, which leads the PS to a metastable triplet state; and molecular oxygen, which earns the energy absorbed by the PS, reaching a high oxidative potential singlet state. The technique has found sucess on the treatment of lesions as cancer. However, it finds difficulties for its dosimetry stablishment, like the quantification of PS distribuition in a photosensitized tissue. This work has three purposes: obtainance of fluorophores quantitative information into turbid media through fluorescence spectroscopy; to show the distribution of the PS Photogem® in healthy Wistar rats’ livers and its consequences on dosimetry; and the upgrade of an existing model for depth of necrosis (Ynec) forecast. There were three experimental stages: the first one was an attemp to rebuild a healthy liver spectrum from a composition using mathematical weights for isolate liver endogenous fluorophores spectra. On the second stage, in vitro and in vivo studies were performed using Coralim-Mix® blue, green and red food dyes and the Exciton® dyes Coumarin-480 and LDS-722, aiming to recover dyes spectra from dyes in turbid solutions and dyes mixtures. On the third one, Photogem® was administered to Wistar rats and fluorescence was collected on rats’ livers, and a relationship was stablished between the changes on fluorescence intensity, PS concentration in the tissue and necrosis profiles obtained via PDT. Results were applied to the upgrade of the Ynec forecast model. Spectra rebuilding, as well as dyes spectra recovering, were not completely reached. Results showed that a great deal of factors contribute to distortions at the collected fluorescence. It was verified that PS distribution is inhomogeneous in a photosensitized organ. It was found a function for the PS tissue distribution and it made possible to upgrade the Ynec forecast model. It was showed that medium turbidity affects in a complex manner the collected fluorescence, making difficult to quantify directly fluorophores in such medium. A need to go deeper into the investigation of light interactions with turbid media so that we may remove distortions they introduce into fluorescence spectra became evident. It was also showed how important is to track PS distribuition in a photosensitized tissue as a part of PDT dosimetry, and how fluorescence spectroscopy seems to be appropriate to perform such tracking, as long as the difficulties on fluorescence collection are overcome.

Δοσιμετρία είναι ο κλάδος της επιστήμης που ασχολείται με τις μετρήσεις ιοντιζουσών ακτινοβολιών, με σκοπό την ποσοτική έκφραση της σχέσης μεταξύ των χαρακτηριστικών ενός πεδίου ακτινοβόλησης και του αποτελέσματος της ακτινοβόλησης ενός συστήματος. Η δοσιμετρία συνεισφέρει σημαντικά σε όσες επιστήμες κάνουν χρήση ιοντιζουσών ακτινοβολιών, και ιδιαίτερα στο χώρο της Ιατρικής, απ’ όπου και πρωτοξεκίνησε η εφαρμογή της. Υπάρχουν πολλές μέθοδοι δοσιμετρίας, και φυσικά, πολλά διαφορετικά είδη δοσιμέτρων. Στη συγκεκριμένη εργασία θα ασχοληθούμε αποκλειστικά με τη δοσιμετρία θερμοφωταύγειας. Το φαινόμενο της θερμοφωταύγειας βρίσκει πρακτική εφαρμογή στη δοσιμετρία ιοντιζουσών ακτινοβολιών με τη συλλογή των οπτικών φωτονίων που εκπέμπονται κατά την αποδιέγερση του θερμοφωταυγάζοντος υλικού, που χρησιμοποιείται. Η μέθοδος της θερμοφωταύγειας αποτελεί την πιο αξιόπιστη μέθοδο για την μέτρηση δόσεων ακτινοβολίας από ιατρικές εξετάσεις. Οι εφαρμογές της δοσιμετρίας θερμοφωταύγειας στην Ιατρική αφορούν κυρίως μετρήσεις της απορροφούμενης δόσεως στην Ακτινοθεραπεία και την Ακτινοδιαγνωστική, ενώ εφαρμόζεται σε μικρότερο βαθμό και στην Πυρηνική Ιατρική. Σκοπός της συγκεκριμένης εργασίας είναι η μέτρηση δόσεων ασθενών, που υποβάλλονται σε ακτινοδιαγνωστικές εξετάσεις, με τη βοήθεια κρυστάλλων θερμοφωταύγειας. Στην Ακτινοδιαγνωστική, η ανάγκη της δοσιμέτρησης προκύπτει από τις επιταγές της Ακτινοπροστασίας, η οποία απαιτεί τη μικρότερη δυνατή δόση στον ασθενή και το προσωπικό, με την καλύτερη δυνατή ποιότητα απεικόνισης. Κι η ανάγκη αυτή γίνεται πιο επιτακτική, όταν οι ακτινοδιαγνωστικές εξετάσεις αφορούν νεογνά και μικρά παιδιά, καθώς και συγκεκριμένες ομάδες του πληθυσμού που χαρακτηρίζονται από υψηλό βαθμό ακτινοευαισθησίας. Πιο συγκεκριμένα, καλούμαστε να υπολογίσουμε την δόση που λαμβάνουν ασθενείς στον θυροειδή αδένα, όταν υποβάλλονται σε εξέταση οισοφαγογραφήματος που πραγματοποιούνται προκειμένου να ελεγχθεί η φυσιολογία και η λειτουργία του πεπτικού συστήματος. Παράλληλα, καλούμαστε να εκτιμήσουμε τον τυχόν κίνδυνο καρκινογένεσης, λόγω των στοχαστικών αποτελεσμάτων της ακτινοβολίας, έπειτα από συσχέτιση με την τιμή της απορροφούμενης δόσης που προκύπτει.
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The basic aim was to briefly present a method for implementing an effective IVD program i.e., a program which would produce the maximum results in the minimum time with the minimum effort. In this work the response of a commercially available diode dosimetry system was studied for two energy qualities, 6MV and 15 MV. Diodes were calibrated against ionization chambers. Signal stability post-irradiation, intrinsic precision, linearity of response with dose and dose decrease under the diode were studied. For each beam energy the response of the diode relative to the given dose as measured by an ionization chamber was evaluated. Diode was calibrated for every energy to give entrance dose, exit dose and eventually the midline dose. Entrance and exit correction factors for field size, tray, source to skin distance, angle and wedge were determined. It was found that diode response i.e. diode reading per cGy of given dose varies significantly with treatment beam set-up. Finally the effects of dose rate, temperature and accumulated dose on the diode’s response were studied.

The specific nature of work in nuclear medicine departments involves the use of isotopes and handling procedures, which contribute to the considerable value of the equivalent dose received, in particular, by the fingertips. Workers of nuclear medicine units who label radiopharmaceuticals are exposed to ionizing radiation. The doses of nuclear medicine workers determined by individual dosimeters, which supply data on the magnitude of personal dose equivalent. The dosimetry pointing to a considerable optimization of the radiological protection among that professional group. However, the problem of the excessive hand exposure had been noted already in the early 1980s. Systematic studies were undertaken in West Scotland. The difficulties associated with automation of radiopharmaceutical preparation process are responsible for the continuing growth of exposure to the hands of the workers. Similar studies have also been undertaken, e.g. in Chile, Norway, Australia, Italy, USA, Belgium(1). In each case, special attention has been paid to the exposure of nuclear medicine worker hands. The radiopharmacists who label various ligands can be exposed to high radiation doses to their fingertips (primarily of the thumb, index finger and middle finger). Quite frequently, the Hp(0.07) to the fingertips of those three fingers may exceed the dose limit, i.e. value of 500 mSv/y for the skin of human fingers, this dose limit refers to the maximum dose recorded(2). Specific difficulty in assessing the exposures of the most affected finger parts is aggravated by the fact that the universally employed method for the determination of the radiation doses received by the hands using a ring with attached thermoluminescence detectors is not adequate in this particular case. This measurement method is inadequate because distribution of the doses received by the skin of the hands and fingers is extremely non uniform. The main aim of the study was to measure the absorbed dose at the hands of the personnel by using thermoluminescent detectors
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Ενώ υπάρχουν πολλές μελέτες που ασχολούνται με ένα συγκεκριμένο ακτινολογικό σύστημα ή συγκρίνουν δύο παρόμοια, η διαφορά στην μελέτη μας είναι ότι μετρούνται πέντε διαφορετικά συστήματα με τα ίδια ακριβώς δοσίμετρα και το ίδιο ακριβώς phantom. Ο σκοπός της έρευνας αυτής είναι να συγκρίνει τις δόσεις τις οποίες λαμβάνει ο εξεταζόμενος από διαφορετικά οδοντιατρικά ακτινολογικά συστήματα. Τα ακτινολογικά συστήματα που προτιμήθηκαν για να συμμετάσχουν στην μελέτη είναι τα παρακάτω: 1) Οδοντιατρικό Σύστημα (Οπισθοφατνιακό) 2) Κεφαλομετρικό Σύστημα 3) Πανοραμικό Σύστημα 4) Υπολογιστικός Τομογράφος (CT) 5) Υπολογιστικός Τομογράφος Κωνικής Δέσμης (Cone Beam CT) Για να μπορέσουμε να έχουμε ακριβείς μετρήσεις στα ευαίσθητα σημεία, όπως π.χ στον εγκέφαλο, στο εσωτερικό του οισοφάγου ή στους υπογνάθιους αδένες προτιμήθηκε αντί να γίνουν οι μετρήσεις απευθείας σε ασθενείς να τοποθετήσουμε τα δοσίμετρα σε ένα RANDO phantom. Με τον τρόπο αυτό πετύχαμε μέτρηση της δόσης στο ακριβές σημείο ενδιαφέροντος. Τα δοσίμετρα που χρησιμοποιήθηκαν ήταν δοσίμετρα θερμοφωταύγειας (TLD), τα οποία προτιμήθηκαν καθώς, όπως θα δούμε στην συνέχεια, διαθέτουν στοιχεία που βοήθησαν πολύ στην διαδικασία των μετρήσεων. Τα δοσίμετρα που χρησιμοποιήθηκαν ανήκουν στο Πανεπιστημιακό Γενικό Νοσοκομείο «Αττικόν». Το phantom που χρησιμοποιήθηκε διατέθηκε από το Διαγνωστικό και Θεραπευτικό Κέντρο «Υγεία» και οι μετρήσεις πραγματοποιήθηκαν τόσο στην Πάτρα όσο και στην Αθήνα. Οι ακτινοβολήσεις για το οπισθοφατνιακό, το πανοραμικό σύστημα και τον υπολογιστικό τομογράφο πραγματοποιήθηκαν στο «Ολύμπιον Θεραπευτήριο» στην Πάτρα, για το κεφαλομετρικό στο Ακτινοδιαγνωστικό Κέντρο Ψηφιακής Απεικόνισης του κ. Σωτήρη Α. Αποστολόπουλου ενώ οι μετρήσεις του Cone Beam CT έγιναν στην Αθήνα, στο Ακτινοδιαγνωστικό Κέντρο της κ. Καρέλη. Η εργασία είναι χωρισμένη σε 4 Κεφάλαια, τα οποία ασχολούνται με τα εξής: Στο Κεφάλαιο 1 θα γίνει μία συνοπτική παρουσίαση των αποτελεσμάτων άλλων μελετών που έχουν πραγματοποιηθεί και είναι σχετικές με την έρευνα που πραγματοποιήσαμε. Στο Κεφάλαιο 2 θα γίνει μία αναλυτική παρουσίαση των υλικών που χρησιμοποιήθηκαν στην έρευνα καθώς και της διαδικασίας που ακολουθήθηκε για να φτάσουμε στα αποτελέσματά μας. Στο Κεφάλαιο 3 θα γίνει η παρουσίαση των αποτελεσμάτων μας. Στο Κεφάλαιο 4 θα πραγματοποιηθεί σχολιασμός των αποτελεσμάτων και σύγκριση με τα δεδομένα που παρουσιάστηκαν στο Κεφάλαιο 1, έτσι ώστε να διαπιστωθεί η πιστότητά τους.
Dose comparison for different dental radiology units using RANDO Phantom.

碩士
國立陽明大學
放射醫學科學研究所
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Brachytherapy, consists of placing sealed radioactive sources very close to or in contact with the malignant tumor, has been widely used in the treatment of cancer for a long time. In recent years, the development of remote control after-loading machine has enhanced the accuracy of treatment delivery. Some clinical applications of brachytherapy, like the brain implant, nasopharyngeal intracavitary, intrabronchial insertion, and mold therapy, are increasingly used. Most of previous studies focused on the dosimetry around an Iridium-192 in water. The purpose of our project is to analyze the dose distributions in heterogeneities phantom materials, like bone and lung. A Monte Carlo simulation has been used to calculate the dose distributions in water, bone and lung. The radial dose functions and anisotropy functions in water are in agreement with published data. The radial dose functions in bone decrease upon depth more than those in water, and the differences are ranging from 0 to 21%. In contrast, the dose distribution in lung shows less attenuation and scatters than that in water. TLD measurements are also performed to verify the results of EGS4 simulation. The measurements and calculations are in agreement to each other where the radial distance is larger than 3 cm.

RESUMO - Os familiares/cuidadores dos doentes que realizaram terapêutica da tiroide com 131I estão sujeitos a três potenciais tipos de exposição a radiações ionizantes: exposição externa, contaminação interna pela ingestão ou absorção do 131I e contaminação interna por inalação de 131I volatilizado no ar. O objetivo deste estudo é avaliar a exposição interna e externa a 131I dos familiares/cuidadores, que coabitam com doentes submetidos a terapêutica com 131I, para hipertiroidismo (Hiper) ou Carcinoma Diferenciado da Tiroide (CDT). O contributo inovador deste estudo assenta na avaliação da dose de exposição e da contaminação internas dos familiares/cuidadores a 131I, paralelamente à dose de exposição externa. Metodologia: Estudo analítico transversal em duas instituições de saúde, cuja amostra por conveniência incluiu 68 doentes submetidos a terapêutica para Hiper ou CDT e 113 indivíduos seus familiares/cuidadores. Mediram-se as grandezas dosimétricas Hp(10) e Hp(0,07) em 83 familiares/cuidadores, com dosímetros TLD durante 21 dias. Mediu-se por espectrometria gama a concentração de atividade de 131I na urina de 34 familiares/cuidadores, após 72 horas de contacto com o doente. Resultados: A atividade média administrada de 131I foi de 2730,8 ± 1603,2 MBq e o débito de dose efetiva (DDE) médio medido a 1 metro foi 12,8 ± 7,6 μSv.h-1. O valor de Hp(10)efetivo médio nos familiares/cuidadores foi de 0,19 ± 0,46 mSv e o valor de Hp(0,07)efetivo foi de 0,18 ± 0,45 mSv. Existe evidência de que a distribuição do Hp(10) não é a mesma entre as categorias da atividade de 131I (2(4) = 296,86; p <0,01) nem do DDE (2(4) = 14,90; p <0,01). Dos 34 familiares/cuidadores apenas em 3 não se detetou 131I na urina. A concentração de atividade média de 131I na urina foi de 97,43 ± 261,24 Bq.L-1. Existe uma forte correlação entre o DDE e o 131I na urina (ρsp = 0,730; p <0,01). Discussão/Conclusões: Existe exposição interna e externa a 131I dos familiares/cuidadores dos doentes envolvidos no estudo. Os valores medidos da dose de exposição externa são inferiores aos limites propostos pela ICRP 97 (1998), ICRP 94 (2004) e os regulamentados em Portugal. Os valores medidos da concentração de atividade na urina devido a contaminação interna não representam perigosidade radiológica para os indivíduos expostos.
ABSTRACT - Family members (FMs) /caregivers of the patients who experience 131I thyroid therapy are potentially exposed to three types of radiation exposures: external exposure, internal contamination from ingestion or absorption of 131I, and internal contamination by 131I inhalation. This study aimed at evaluating the internal and external exposure to 131I of FMs/caregivers who live with patients undergoing 131I therapy for hyperthyroidism (Hyper) and differentiated thyroid carcinoma (DTC). The innovative contribution of this work stems from the assessment of the internal exposure dose and contamination of the FMs/caregivers to 131I, in parallel to the external exposure dose. Methodology: A cross-sectional analytical study was performed in two health institutions, with a convenience sample comprising 68 patients undergoing therapy for Hyper or DTC and 113 FMs/caregivers. For 21 days, the dosimetric quantities Hp(10) and Hp(0.07) were measured in 83 FMs/caregivers using TLD dosimeters. Post 72 hours of patient-contact, the activity concentration of 131I in the urine of the 34 FMs/caregivers was measured using gamma spectrometry. Results: The mean activity of 131I administered was 2730.8 ± 1603.2 MBq and the average value of the measured effective dose rate (EDR) measure at 1 meter was 12.8 ± 7.6 μSv.h-1. The average value of Hp(10)effective measured among the FMs/caregivers was 0.19 ± 0.46 mSv and the average value of Hp(0.07)effective was 0.18 ± 0.45 mSv. There is evidence that the distribution of Hp(10) is not the same among the categories of 131I activity (2(4) = 296,86; p <0.01), neither the EDR one (2(4) = 14,90; p <0.01). Of the 34 FMs/caregivers, for only 3 131I was not detected in the urine. The mean activity concentration of 131I in the urine was 97.43 ± 261.24 Bq.L-1. A strong correlation between the EDR and the 131I in the urine (ρsp = 0.730; p <0.01) was observed. Discussion/Conclusions: FMs/caregivers undergo both internal and external exposure to 131I. The measured external exposure dose values are below the limits proposed by ICRP 97 (1998), ICRP 94 (2004) and those available in the Portuguese regulations. The measured values of activity concentration in the urine due to internal contamination do not represent a radiological hazard for the exposed individuals.