Lungscintigrafi är en av de mest vanligt förekommande nuklearmedicinska undersökningarna. Akut lungemboli är en huvudindikation för lungscintigrafi. Undersökningen består av två delar, först undersöks ventilationsdelen och sedan perfusions-fördelningen i lungan. Vid ventilationen inhalerar patienten 99mTc-Technegas. Vid perfusionen injiceras 99mTc-Pulmocis (MAA) intravenöst. Enligt EANM ligger den administrerade aktiviteten mellan 25 – 30 MBq för Technegas och mellan 140 – 160 MBq för Pulmocis. Studien utfördes på avdelningen klinisk fysiologi vid Centralsjukhuset Kristianstad. Först utfördes en fantomstudie före patientstudien för att testa metoden. Den inkluderade totalt 20 patienter som hade en bokad tid för lungscintigrafi. Syftet med studien var att optimera metoden för lungscintigrafi genom att reducera patientstråldosen genom att uppskatta aktiviteten som administreras vid ventilation. Vidare var syftet att kontrollera om kvoten mellan ventilation- och perfussionsundersökningen överensstämmer. Detta utfördes med hjälp av två metoder: den ena var en gammadetektor som mätte antalet counts som patienten har andats in och den andra var med att kvantifiera bilderna efter en slutförd undersökning. Resultaten över aktiviteten i ventilationsbilderna i Xeleris Software har erhållits med en beräkning. Perfusionen beräknades genom att mäta sprutans aktivitet före och efter undersökningen. Genom dessa värden kunde kvoten mellan perfusion och ventilation erhållas. Medelvärdet för alla patienter visar att kvoten blir fyra gånger så hög i perfusion som i ventilation. Resultaten över mätmetoderna visade att gammadetektorn har samma effektivitet som kamerans detektorer. Det erhölls en positiv korrelationskoefficient mellan metoderna och den låg på 0,79. Med Bland-Altmans diagram var 95% av värden för båda metoderna inom referensramarna förutom ett extremvärde som berodde på en hög inhalerad aktivitet. Slutsatsen blir att mätmetoden kräver en större studie med fler deltagare för att kunna implementera mätningen med gammadetektorn i kliniken. / Pulmonary scintigraphy is one of the most common nuclear medicine examinations. Acute pulmonary embolism is a major indication for pulmonary scintigraphy. The examination consists of two parts, first the ventilation part and then the perfusion distribution in the lung is examined. During ventilation, the patient inhales 99mTc-Technegas. At perfusion, 99m Tc-Pulmocis (MAA) is injected intravenously. According to EANM, the administered activity is between 25 - 30 MBq for Technegas and between 140 - 160 MBq for Pulmocis. The study was performed at the department of Clinical physiology at Central Hospital Kristianstad. A phantom study was first performed before the patient study to test the method. It included a total of 20 patients who had an appointment for pulmonary scintigraphy. The aim of the study was to optimize the method of pulmonary scintigraphy by reducing the patient radiation dose by estimating the activity administered during ventilation and perfusion. Furthermore, the aim was to check whether the ratio between the ventilation and perfusion examination is correct. This was done using two methods: one was a gamma detector that measured the number of counts that the patient has inhaled, and the other was involved in quantifying the images after a completed examination. The results of the activity in the ventilation images in Xeleris Software have been calculated. Perfusion is calculated by measuring the activity of the syringe before and after the examination. Through these values, the ratio between perfusion and ventilation could be obtained. The average value for the ratio and diagrams showed that the ratio is four times as much in perfusion as in ventilation. The results of the measurement methods showed that the gamma detector has the same efficiency as the camera detectors. A correlation coefficient was maintained between methods that indicated a good significance. With Bland-Altman's diagram, 95% of the values ​​for both methods were within the frame of reference except for an extreme value that was due to a high inhaled activity. The conclusion is that the measurement method requires a larger study with more participants to be able to implement the measurement with the gamma detector in clinical practice.

Antal datortomografiundersökningar har ökat under flera år i Sverige tack vare tekniska utvecklingar och ökad tillgänglighet på sjukvård. Södertälje sjukhus röntgenavdelningen är i behov av att byta ut en utdaterad datortomograf (eng: Computed tomography, CT) och avdelningen för medicinsk teknik har föreslagit ett inköp av en CT med fotonräknande-detektor. Bilddata framställdes genom en fantomstudie för att påvisa förhållandet mellanstråldosparametern CTDIvol och kontrast-brus-förhållandet (CNR) hos CT-systemen: SOMATOM Drive och NAEOTOM Alpha. Den genererade datan påvisade att det finns en väsentlig skillnad i CNR-CTDIvol-förhållandet mellan SOMATOM Drive och NAEOTOM Alpha. Resultaten tydliggör att NAEOTOM Alpha kan producera bilder med betydligt mindre brus vid lägre stråldoser. Ett inköp av en fotonräknande detektor CT skulle kunna rättfärdigas utifrån bildkvalitéförbättringen som systemet kan erbjuda. / The number of computed tomography (CT) scans has increased during the past years in Sweden due to technical advancements and increased availability of healthcare. The x-ray department at Södertälje hospital is in need of replacing an outdated computed tomography and the departmentof clinical engineering has proposed a purchase of a photon-counting detector CT. Image data was produced through a phantom study to demonstrate the relationship between the parameter CTDIvol radiation dose and the contrast-to-noise ratio (CNR) of the CT systems: SOMATOM Drive and NAEOTOM Alpha. The generated data demonstrated that there is a substantial difference in the CNR-CTDIvol relationship between SOMATOM Drive and NAEOTOM Alpha. The results entail that NAEOTOM Alpha can produce images with considerably less noise at lower radiation doses. The purchase of a photon-counting CT could be justified by the improved image quality it can offer.

Yes / Dynamic X-ray imaging systems are used for interventional cardiac procedures to treat coronary heart disease. X-ray settings are controlled automatically by specially-designed X-ray dose control mechanisms whose role is to ensure an adequate level of image quality is maintained with an acceptable radiation dose to the patient. Current commonplace dose control designs quantify image quality by performing a simple technical measurement directly from the image. However, the utility of cardiac X-ray images is in their interpretation by a cardiologist during an interventional procedure, rather than in a technical measurement. With the long term goal of devising a clinically-relevant image quality metric for an intelligent dose control system, we aim to investigate the relationship of image noise with clinical professionals’ perception of dynamic image sequences. Computer-generated noise was added, in incremental amounts, to angiograms of five different patients selected to represent the range of adult cardiac patient sizes. A two alternative forced choice staircase experiment was used to determine the amount of noise which can be added to a patient image sequences without changing image quality as perceived by clinical professionals. Twenty-five viewing sessions (five for each patient) were completed by thirteen observers. Results demonstrated scope to increase the noise of cardiac X-ray images by up to 21% ± 8% before it is noticeable by clinical professionals. This indicates a potential for 21% radiation dose reduction since X-ray image noise and radiation dose are directly related; this would be beneficial to both patients and personnel. / This work was funded by Philips Healthcare, NL. Part of this work has been performed in the project PANORAMA, cofunded by grants from Belgium, Italy, France, the Netherlands, and the United Kingdom, and the ENIAC Joint Undertaking.

The aim of this study is to determination of local diagnostic reference levels for radiodiagnostic examination in the General Teaching Hospital in Prague. Local diagnostic reference levels are used for an evaluation of radiation load which patients receive during medical examinations of specific parts of the human body. The evaluation can be on the level of a hospital and its department or on the level of concrete X-ray machine. The theoretical part describes a ionizing radiation, including its interaction with matter, creating, formation of radiodiagnostic image, legislation during optimization of radiodiagnostic examination, radiological protection and determination of values for radiation dose. The practical part describes the determination of local diagnostic reference levels with the help of entrance surface kerma and the median dose in the mammary gland. Both of these variables are relevant for determination of the risk of adverse effects of ionizing radiation which is applied during radiographic examination. Data for this study was collected with the help of operating diaries and PACS system. It has been rated twenty-six kinds of examinations from twelve mobile and nine stationary (including two mammographs) X-ray machines. All resulting values were statistically processed and compared with...

CONTEXTO E OBJETIVO: O manejo do carcinoma hepatocelular (HCC) é desafiador devido a agressividade tumoral e cirrose associada. Faltam opções locais efetivas após falha à quimioembolização transarterial (TACE). Nosso objetivo foi testar através de estudo prospectivo fase II, a eficácia e segurança da Radioterapia Estereotáctica Corpórea (SBRT) em pacientes com HCC e resposta parcial ou contraindicação à TACE. MÉTODO: Pacientes com até 5 lesões de HCC restritas ao fígado realizaram SBRT na dose de 30 a 50 Gy em 5 frações. O desfecho primário foi sobrevida livre de progressão das lesões tratadas. Os desfechos secundários foram sobrevida livre de progressão hepática, sobrevida livre de progressão a distância, sobrevida global e toxicidade. Este estudo está registrado em clinicaltrials.gov sob o número NCT02221778. RESULTADO: De novembro de 2014 a junho de 2018, 19 pacientes receberam SBRT na dose mediana de 40 Gy (range 30 - 50 Gy). Todos tinham escore de Child Pugh A. A idade mediana foi de 67 anos (range 42-84 anos). A doença de base foi hepatite C em 42%, hepatite B em 26% e álcool em 26%. TACE prévia foi realizada em 84% dos pacientes, com mediana de duas TACEs (range 0-5). O número mediano de lesões foi dois (range 1-4), com tamanho mediano de 4 cm (1,5-10 cm). 32% dos pacientes tinham trombose tumoral; a AFP mediana pré-tratamento foi de 142,5 ng/ml (range 4,2 - 5 494 ng/ml). A sobrevida livre de progressão local em 1 ano foi de 80% (IC95%, 50% a 93%). A sobrevida livre de progressão hepática, sobrevida livre de progressão a distância e sobrevida global em 1 ano foram, respectivamente, de 52%, 82% e 84%. Não houve toxicidades clínicas grau 3 ou 4. Toxicidades laboratoriais até grau 3 ocorreram em 3 pacientes (16%). Resposta radiológica completa foi atingida em 53% dos pacientes, 42% tiveram resposta parcial. O tempo mediano para melhor resposta foi de 3,4 meses (range 2,4-12,6 meses). CONCLUSÃO: A SBRT é uma opção eficaz, segura e não invasiva em pacientes com HCC e resposta parcial ou contraindicação à quimioembolização / BACKGROUND AND PURPOUSE: Management of hepatocellular carcinoma (HCC) is challenging due to tumor aggressiveness and associated cirrhosis. There is paucity of effective local options after failure of transarterial chemoembolization (TACE). Our objective was to test in the setting of a phase II prospective study, the efficacy and safety of Stereotactic Body Radiation Therapy (SBRT) in patients with partial response or unsuitable for TACE. METHODS: Patients with HCC and up to five liver-only lesions received SBRT 30 to 50 Gy in 5 fractions. Primary endpoint was local progression-free survival. Secondary endpoints were liver progression-free survival, distant progression-free survival, overall survival and toxicity. This study is registered at clinicaltrials.gov NCT02221778. RESULTS: From Nov 2014 through Jun 2018, 19 patients received SBRT with a median dose of 40Gy (range 30 - 50 Gy). All patients were Child Pugh A. Median age was 67 years old (range 42-84y). Underlying liver disease was hepatitis C in 42% of patients, hepatitis B in 26% and alcohol-related in 26%. 84% received previous TACE, with a median of two TACEs (range 0-5). Patients had a median of two lesions (range 1-4), with median size of 4 cm (1.5-10 cm). 32% had tumor vascular thrombosis; median pretreatment AFP was 142.5 ng/ml (range 4.2 - 5,494 ng/ml). 1y local progression-free survival was 80% (95% CI, 50% to 93%). 1y liver progression-free survival, distant progression-free survival and overall survival were, respectively, 52%, 82% and 84%. No patient had clinical grade 3 or 4 toxicities. Laboratory toxicities up to grade 3 occurred in three patients (16%). Complete radiological response was seen in 53% of patients, 42% had partial response. Median time for best response was 3.4 months (range 2.4-12.6 months). CONCLUSION: SBRT is an effective, safe and noninvasive option in HCC patients with partial response or unsuitable for TACE

Esse trabalho apresenta uma nova metodologia para a correção do espectro de potência do ruído no processo de simulação de aquisições de imagens de tomossíntese digital mamária (Digital Breast Tomosynthesis - DBT) com doses reduzidas de radiação. A simulação é realizada por meio da inserção de ruído quântico dependente do sinal em imagens previamente adquiridas com a dose padrão de radiação. A DBT utiliza a mesma tecnologia de raios X que a mamografia digital, porém com a capacidade de prover ao médico exames do volume tridimensional da mama, minimizando o problema de superposição de tecidos. Apesar de ser o sucessor da mamografia, estudos têm mostrado que a otimização da relação entre a dose de radiação e a qualidade da imagem adquirida ainda não está bem estabelecida na DBT. Devido à impossibilidade de realizar diversas exposições de radiação a uma mesma paciente para os estudos de otimização da dose de radiação, é desejável que exista um método capaz de simular com exatidão diversas exposições tendo como base uma imagem clínica de referência. Embora existam diversos métodos para a simulação da redução de dose em exames mamográficos, o mesmo não pode ser dito quanto a imagens de DBT. O método desenvolvido para simulação da redução da dose de radiação em imagens de DBT se baseia em uma abordagem de inserção de ruído por meio de uma transformada de estabilização de variância, que já foi utilizada para simulação da redução de dose em exames de mamografia digital. Porém, esse trabalho propõe a inclusão da correção do espectro de potência do ruído para otimizar o desempenho do método de inserção de ruído para exames de DBT. Os resultados obtidos mostraram que, quando comparando a imagens de referência, a as imagens simuladas apresentaram erro menores que 1% para a análise do valor médio e desvio padrão e erro próximo de 5% para a análise do espectro de potência, apresentado resultados até 64% melhores que métodos não otimizados para DBT. / This work presents a new methodology for noise power spectrum correction in the simulation of digital breast tomosynthesis (DBT) images with reduced dose of radiation. The simulation is performed by inserting a signal-dependent quantum noise into previously acquired images with the standard dose of radiation. Using the same X-ray technology as a standard mammography, the DBT is capable of reconstructing the inner tissues of the patients\' breasts as a three-dimensional volume, providing more resources for cancer detection than its bi-dimensional counterpart and minimizing tissue overlapping. Despite being the successor to mammography, studies have shown that the optimization of the relationship between radiation dose and image quality is not well established in DBT yet. Due to the impossibility of exposing the same patient to multiple exams with different doses each, a simulation method able to mimic clinical images with high reliability is desirable. Despite the number of methods proposed for dose reduction simulation in mammography, scarcely any may be used in DBT. The method developed for simulation of radiation dose reduction in DBT images is based on a noise insertion approach using a variance-stabilizing transformation, which has already been used to simulate dose reduction in digital mammography exams. However, this work proposes the inclusion of the noise power spectrum correction to optimize the performance of the noise insertion method for DBT exams. The results showed that, when compared with reference images, the simulated images achieved less than 1% error for mean and standard deviation values and close to 5% error for power spectrum analysis, improving in up to 64% when compared with non-optimized for DBT simulation methods.

Das ARDS gilt, trotz verschiedenster Möglichkeiten der intensivmedizinischen Therapie, immer noch als die schwerste Form einer Lungenparenchymverletzung mit einer hohen Letalität. Zu Beginn der Erkrankung zeigt sich eine große Diskrepanz zwischen zunehmender Hypoxie und blandem Röntgen-Thorax-Befund. Die Röntgen-Thorax-Aufnahme bildet somit einen wichtigen diagnostischen Bestandteil. Die Kriterien einer einfachen Durchführung, guten Reproduzierbarkeit, hohen Aussagekraft und der Möglichkeit einer Verlaufsbeurteilung machen die Röntgen-Thorax-Liegendaufnahme zu einem wichtigen Bestandteil der intensivmedizinischen Diagnostik. Untersucht wurden retrospektiv 1575 Röntgen-Thorax-Aufnahmen von 33 Patienten mit dem Krankheitsbild des ARDS. Das Patientenkollektiv setzte sich aus 14 Frauen und 19 Männern im Alter von 12 bis 63 Jahren zusammen. Die Überlebensrate des untersuchten Patientenkollektives betrug 87,9%. Pro Patient wurden durchschnittlich 48 Röntgen-Thorax-Aufnahmen (zwischen 10 und 148 Aufnahmen) angefertigt. Die Aufnahmen wurden im Hinblick auf ihre Qualität, Strahlenexposition und ihre Übereinstimmung mit klinischen Parametern untersucht. Für die Beurteilung der Inter- und Intraobservervariabilität wurden verschiedenen Untersuchern 60 Röntgen-Thorax-Aufnahmen exemplarisch zur Bewertung vorgelegt. Aufgrund der schwierigen Aufnahmebedingungen bei Intensivpatienten sind verdrehte und verkippte Röntgen-Thorax-Aufnahmen nicht zu vermeiden. Trotz dieser Qualitätseinbußen ist ihr Informationsgehalt ein wichtiges Kriterium der intensivmedizinischen Diagnose und Therapie. Die Strahlenexposition der Röntgen-Thorax-Liegendaufnahmen und der daraus zu errechnende Lebenszeitverlust sind im Hinblick auf die Schwere und die hohe Letalität der Grunderkrankung als verschwindend gering zu betrachten. Die Röntgen-Scores nach Murray, Morel, Miniati, Rommelsheim und Ostendorf sind in der Diagnostik und Verlaufsbeurteilung des ARDS weit verbreitet. Sie sind in Handhabung und Gewichtung der Veränderungen jedoch sehr unterschiedlich. Zusammenhänge zwischen klinischen Parametern konnten für alle Scores, sowie für einen neuen Score beobachtet werden. Dabei ergaben sich für alle Scores ähnliche Beziehungen. Unter Berücksichtigung der Handhabung der einzelnen Röntgen-Scores, der Inter- und Intraobservervariabilität, sowie der Übereinstimmung mit klinischen Parametern sind der Röntgen-Score nach Rommelsheim, sowie der neue Röntgen-Score für den klinischen Alltag zu empfehlen. / Radiological Quantification of Chest X-Rays of the Lung Oedema of Patients with Adult Respiratory Distress Syndrome (ARDS) The ARDS is still regarded as the most serious form of lung parenchyma injury with a high lethality in spite of various possibilities of intensive care therapies. In the beginning of the illness a high discrepancy between an increasing hypoxia and a mostly inconspicouos chest X-ray result can be observed. Therefore, the chest X-ray forms an essential part of the diagnostic basis. It is characterized by simple implementation, a good reproducibility, a high meaningfulness and the possibility to judge the course of the illness. This makes the chest X-ray very valuable for the intensive care diagnosis. 1575 chest X-rays from 33 patients with ARDS symptoms were evaluated. The patients consisted of 14 women and 19 men between 12 and 63 years of age. The overall survival rate for all patients was 87.9%. An average of 48 (ranging from 10 to 148) chest X-rays were taken per patient. They were examined with regard to quality, radiation dose and correspondence to clinical variables. In order to judge the interobserver and intraobserver variability 60 chest X-rays were evaluated by different examiners. Due to the difficult conditions while taking the chest X-rays distorted and tilted chest X-rays cannot be avoided. Despite this loss of quality their content of information is an important criterion for the intensive care diagnosis and treatment. The loss of lifetime due to the radiation dose received can be ignored compared to the severeness and the high lethality of the basic illness. The chest X-ray scores according to Murray, Morel, Miniati, Rommelsheim and Ostendorf are commonly used for diagnostic purposes and to judge the course of the ARDS. However, their handling and their weightning of changes varies a lot. Correlations between all scores, a new score and the clinical variables were observed. All scores, including the new score, showed similar relations between the score ranking and the clinical variables. Considering the handling of the different chest X-ray scores, their interobserver and intraobserver variability and their correlation to clinical variables the chest X-ray score according to Rommelsheim and the new score can be recommended for daily use.

Purpose: To develop a Ray Cast/Dose Superposition (RC/DS) algorithm for proton grid therapy. Its functionality needed to include automatic positioning of small proton pencil beams in a grid-pattern and superimposing thin beam Monte Carlo (MC) dose distribution data on a Computer Tomography (CT) density volume. The purpose was to calculate and store un-weighted volumetric dose distributions of individual proton energies for subsequent optimization. Materials & Methods: Using the programming language Python 3.6, CT and Volume Of Interest (VOI) data of various patients and phantoms were imported. The target VOI was projected to either two or four planes, corresponding to the number of used gantry positions. Rays were then traced through the CT voxels, which were converted from Hounseld Units to density using a look up table, to calculate Water Equivalent Distance and proton energy needed to reach the proximal and distal edge of the target volume. With automated grid-pattern beam positioning, thin beam MC calculated depth dose distribution files were interpolated, scaled and superimposed on the CT volume for all beamlet positions. The algorithm reliability was tested on several CT image sets, the proton range estimation compared to a commercial TPS and the depth dose interpolation analyzed using MC simulations. Results: The RC/DS algorithm computation time was on average around 6 hours and 30 minutes for each CT set. The dose distribution output visually conformed to target locations and maintained a grid pattern for all tested CT sets. It gave unwanted dose artifacts in situations when rays outside the beamlet center passed a significant length of low/high density regions compared to the center, which yielded dose distributions of unlikely shape. Interpolating MC dose distribution values showed comparability to true MC references of same energy, yielding results with 0.5% difference in relative range and dose. Conclusions: The developed algorithm provides unweighted dose distributions specific for small beam proton grid therapy and has been shown to work for various setups and CT data. Un-optimized code caused longer computation times then intended but was presumed faster than MC simulations of the same setup. Efficiency and accuracy improvements are planed for in future work. / Proton grid therapy group

Comprendre et modéliser le comportement des matériaux sous irradiation électronique est un enjeu important pour l’industrie spatiale. La fiabilité des satellites nécessite de maîtriser et prédire les potentiels de surface s'établissant sur les diélectriques. Ce travail de doctorat a donc pour objectif de caractériser et de modéliser les différents mécanismes physiques (en surface et en volume) gouvernant le potentiel de charges dans les matériaux polymères spatiaux tels que le Téflon® FEP et le Kapton® HN. La mise au point d'un nouveau dispositif et d'un protocole expérimental a permis de corroborer l'existence d’une conductivité latérale des charges, souvent négligée dans les modèles physiques et numériques. Les études paramétriques, révélant l’influence de l’énergie et le flux des électrons incidents, ont permis de brosser un portrait des processus mis en jeu pour le transport (par saut ou par piégeage/dépiégeage) de charges en surface. A la lumière de cette étude, une conductivité équivalente est extraite, assimilant le matériau à un système prenant en compte les mécanismes de transport volumique et surfacique. L'analyse des évolutions non-monotones de potentiel mesurées sur les polymères spatiaux en condition spatiale a permis de révéler une dépendance de la conductivité volumique induite sous irradiation avec la dose reçue. L'étude paramétrique réalisée sur les mécanismes de transport en volume révèle une influence minoritaire du déplacement du barycentre de charges et du vieillissement physicochimique. Un modèle «0D» à un seul niveau de pièges, prenant en compte les mécanismes de piégeage/dépiégeage et recombinaison entre les porteurs de charges, a été développé. Ce modèle simplifié permet de reproduire qualitativement les évolutions de potentiel expérimentales en fonction du débit de dose et lors d'irradiations successives. / Charging behaviours of space dielectric materials, under electron beam irradiation, is of special interest for future spacecraft needs, since this mechanism could induce electrostatic discharges and consequently damages on the sensitive systems on board. In order to assess the risks of charging and discharging, this work aims at understanding the overall charge transport mechanisms and predicting the electrical behaviour of the insulator materials, especially Teflon® FEP and Kapton® HN. For an optimized prediction, the first part of our work is thus to check whether lateral conduction process can take place in the overall charge transport mechanism. Through the definition of a new experimental set-up and protocol, we have been able to discriminate between lateral and bulk conductivity and to reveal the presence of lateral conductivity that is enhanced by radiation ionization processes. We have been able to demonstrate as well that lateral intrinsic conductivity is enhanced with the increase current density and when approaching the sample surface. The second part of our work deals with the characterization of the electrical charging behaviour of Teflon® FEP under multi-energetic electron beam irradiation and the modelling of the overall bulk charge transport mechanisms. An experimental study on charge potential evolution as a function of electron spectrum, electric field, relaxation time, dose and dose rate, was performed. A numerical model has been developed to describe the effect of the different abovementioned mechanisms on the evolution of the surface potential. This model agrees correctly with the experimental phenomenology at qualitative level and therefore allows understanding the physical mechanisms steering charge transport in Teflon® and Kapton®.

Made available in DSpace on 2014-10-09T12:42:01Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:33Z (GMT). No. of bitstreams: 1 19174.pdf: 31751 bytes, checksum: 7f1e1ac2bd5fcea7b8edbb1e6ba7a12b (MD5) / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP