Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-04-08T12:38:10Z No. of bitstreams: 0 / Made available in DSpace on 2016-04-08T12:38:10Z (GMT). No. of bitstreams: 0 / Uma série de testes foi aplicada a medidores portáteis de radiação ionizante para altas taxas de kerma no ar, especificamente medidores do tipo teletector. Estes detectores são do tipo Geiger Müller e são utilizados em rotinas de proteção radiológica em aceleradores, reatores, fontes de alta atividade e ainda em situações de emergência no Brasil, assim como em outros países. Também são encaminhados para calibração no Instituto de Pesquisa Energéticas e Nucleares (IPEN) e foram analisados para estabelecer parâmetros de comportamento destes detectores, especificando as suas sensibilidades e suas características operacionais. Foram realizados testes de variação da leitura dos equipamentos com a tensão da bateria, efeito de geotropismo, dependência energética, dependência angular. Com este testes foi possível determinar as características mais comuns e importantes destes equipamentos permitindo a elaboração de um programa de controle de qualidade. Foram calibrados 17 teletectors durante este trabalho e destes, 10 foram testados. Os testes foram realizados para caracterizar o sis tema gama de irradiação (dosimetria de feixe de radiação) que possui maior atividade e permite testes em medidores do tipo teletectors em uma maior faixa de medição. Desse modo foi feito o aperfeiçoamento do programa de controle de qualidade de medidores portáteis de radiação ionizante para altas taxas de kerma no ar no LCI, oque beneficiou os usuários deste tipo de equipamento, e ainda com medições e calibrações mais consistentes e com melhor controle de qualidade dos processos. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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

Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-04-20T17:12:27Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTAÇÃO FINAL PARA IMPRESSÃO CAPA DURA.compressed.pdf: 5438350 bytes, checksum: 6a32a2d9accc05fb896d407a8a699c4b (MD5) / Made available in DSpace on 2016-04-20T17:12:27Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTAÇÃO FINAL PARA IMPRESSÃO CAPA DURA.compressed.pdf: 5438350 bytes, checksum: 6a32a2d9accc05fb896d407a8a699c4b (MD5) Previous issue date: 2015-05-31 / CAPES / FACEPE / No presente trabalho, foi realizado um levantamento das doses recebidas por pacientes pediátricos, em exames radiográficos convencionais dos seios da face, realizados no Recife, PE. Para a realização do estudo, foram selecionados dois hospitais que atendem ao Sistema Único de Saúde, com alta demanda de exames pediátricos. Os dados dos pacientes e os parâmetros de irradiação utilizados em 159 exames radiográficos dos seios da face de crianças, com idades entre 0 e 15 anos, foram coletados, sendo 103 radiografias realizadas na projeção lateral (radiografia cavum) e 56 radiografias realizadas nas projeções pósteroanteriores em fronto-naso (FN) e mento-naso (MN) (radiografias Caldwell e Waters, respectivamente). Inicialmente, foram efetuadas as avaliações de desempenho dos dois equipamentos de raios X pertencentes aos hospitais. A partir dos valores dos rendimentos dos tubos de raios X e dos parâmetros de irradiação empregados nos exames, foram estimados os valores de kerma no ar na superfície de entrada (Ka,e) e produto kerma no ar-área (PK,A). Os valores de kerma no ar nas regiões dos olhos e da tireoide foram estimados utilizando dosímetros termoluminescentes (TLD-100). As doses absorvidas médias nos órgãos e a dose efetiva foram estimadas com o software PCXMC® a partir dos dados antropométricos, parâmetros de irradiação e do kerma no ar incidente (Ka,i), obtido com o rendimento. Os resultados mostraram que os valores de Ka,e variaram entre 0,065 mGy e 1,113 mGy, para radiografias cavum, entre 0,13 mGy e 7,99 mGy, para radiografias na incidência Caldwell e entre 0,13 mGy e 10,12 mGy, para radiografias na incidência Waters. Os valores do kerma no ar na região dos olhos variaram entre 0,001 mGy e 0,968 mGy, nas radiografias cavum, e 0,011 mGy e 0,427 mGy, nas incidências Caldwelll e Waters (conjuntamente). Na região da tireoide, os valores de kerma no ar variaram entre 5 μGy e 932 μGy, para as radiografias cavum, e 2 μGy e 972 μGy, para as incidências Caldwell e Waters. 90% dos valores de Ka,e estimados para os exames realizados no Hospital B encontram-se dentro do recomendado pela comunidade britânica, enquanto todos no Hospital A encontram-se acima. O fato do Hospital B apresentar valores de Ka,e dentro do aconselhado não significa que seu serviço esteja otimizado, devido a grande quantidade de filmes rejeitados, cuja imagem apresentava-se clara e inapropriada para o diagnóstico, elevando a dose final recebida pelo paciente pela repetição do exame. Os altos valores de Ka,e devem-se, principalmente, à utilização indiscriminada da grade antiespalhamento, não recomendada para pacientes desta idade. Os valores de PK,A variaram entre 5,7 mGy.cm2 e 92,3 mGy.cm2 para as radiografias cavum, entre 24,4 mGy.cm2 e 340,3 mGy.cm2 para as radiografias Caldwell e, entre 34,0 mGy.cm2 e 378,3 mGy.cm2 para as radiografias Waters. A partir dos dados pode-se concluir que há necessidade de otimização dos procedimentos radiográficos. / In this study, a survey was conducted in order to assess doses received by pediatric patients ongoing conventional radiographs of the sinuses, performed in Recife, PE. For the study, two hospitals of SUS (Sistema Único de Saúde), with high demand for pediatric examinations, were selected. Patient data and irradiation parameters were collected for 159 radiographs of the children’s sinuses with ages between 0 and 15. Among those, 103 radiographs were taken on the lateral projection (cavum radiography) and 56 radiographs were taken in posteroanterior projections in fronto-naso (FN) and mento-naso (MN) (Caldwell and Waters radiographs, respectively). Initially, the performance of the two X-ray equipment was evaluated. Air kerma values at the entrance surface (Ka,e), and air kerma area product (PK,A) were estimated using X-ray tubes output and irradiation parameters used in the examinations. Air Kerma values on the eyes and thyroid were estimated using thermoluminescent dosimeters (TLD-100). The average absorbed organ doses and effective dose were estimated at the PCXMC® software using the anthropometric data, irradiation parameters and the incident air kerma (Ka,i) obtained with the x-ray tube output. The results showed that Ka,e values varied between 0.065 and 1.113 mGy for cavum radiographs; between 0.13 and 7.99 mGy for Caldwell’s view; and between 0.13 and 10.12mGy for Waters’ view. The air kerma values in at the eye region varied from 0.001 mGy to 0.968 mGy for cavum radiographs, and from 0.011 mGy to 0.427 mGy for Caldwell and Waters’ views (together). In the thyroid region air kerma values ranged from 5 μGy to 932 μGy for cavum view and from 2 μGy to 972 μGy for Caldwell and Waters’ views. Tests performed at Hospital B have shown that 90% of the Ka,e values estimated during exams are within the recommended values by British Commonwealth, while all the Ka,e values in the Hospital A were above it. However, even though Hospital B presented Ka,e values within recommended values, this service was not optimized, due to the large amount of rejected films, whose image were inappropriate for diagnosis resulting in increased dose by the patient re-examination. The high Ka,e values are due mainly to the indiscriminate use of anti-scatter grid, not recommended for patient ages assessed in this study. PK,A values varied between 5.7 and 92.3 mGy.cm2 for cavum radiographs, between 24.4 and 340.3 mGy.cm2 for Caldwell’s view and between 34.0 and 378.3 mGy.cm2 for Waters’ view. Thus, it was concluded that there is need for optimization of radiographic procedures.

No description available.

In radiation therapy, gel dosimetry is used to measure radiation doses for treatment verification. Gel dosimeters have the ability to record dose information in three dimensions. The objective of this thesis was to fabricate a transparent cryogel radiochromic dosimeter with poly(vinyl alcohol) (PVA) as the gelling agent. A transparent dosimeter may be analyzed using an optical read out technique, which is desirable. PVA cryogels can be made transparent by adding dimethyl sulfoxide (DMSO). Measurements of dose response were performed and various parameters were adjusted, including: numbers of freeze-thaw cycles (FTCs); concentrations of PVA; DMSO concentration. The measured absorption coefficient increased linearly with dose up to approximately 10 Gy. The sensitivity was increased for higher PVA concentrations, larger numbers of FTCs, and less DMSO. The resulting dosimeter was stable and showed no significant dose rate or photon energy dependence. The cryogels were later formed into 5 mm thick films and used as a tool for performing in vivo dosimetry. The dose response of the radiochromic bolus was characterized by irradiating it on a flat surface at different gantry angles. The dose measured in the bolus was approximately 0.80 of the dose measured by Gafchromic film at the skin surface, taking the obliquity into account. IMRT treatments were delivered to a RANDO phantom. The radiochromic bolus was used to measure skin surface dose in two dimensions at various locations. The 0.80 factor was used to calibrate the bolus, which was then compared to an accompanying film measurement. Good agreement was observed between the measurements (>95% gamma pass rate), suggesting the radiochromic bolus may be suitable for in vivo applications. The radiochromic bolus was then used to evaluate errors associated with the breath hold technique often used with left chest wall tangential irradiation. Treatment plan incorporating the radiochromic bolus was delivered at the planned position and shifted anterior-posteriorly (A/P) up to 5 mm. Large discrepancies from the planned two dimensional skin surface distribution were observed for shifts as small as 3 mm in the A/P direction. The study demonstrated that the cryogel was sensitive to small positioning uncertainties for chest wall irradiations, potentially allowing for the detection of clinically relevant errors. Other potential formulations of PVA-based radiochromic cryogels are discussed briefly as avenues to future research projects. / Thesis / Doctor of Philosophy (PhD)

No description available.

<p>Intensity-Modulated Radiation Treatment (IMRT) requires patient-specific quality assurance measurements, which can benefit from the convenience of using an Electronic Portal Imaging Device (EPID) for dose verification. However, EPIDs have limitations stemming from the non-uniform backscatter due to the support-arm as well as from scatter, glare, and an increased sensitivity to low-energy photons. None of these effects is typically accounted for in a treatment planning system (TPS) model, resulting in errors in calculated EPID response of up to 6%. This work addresses the non-uniform backscatter by directly incorporating a support-arm backscatter region into the TPS geometry. The shape of the backscatter region is adjusted iteratively until the TPS-calculated flood-field planar dose matches the flood-field EPID image The scatter, glare and increased low-energy response are addressed by using a radially-dependent Point-Spread Function (Kernel). The kernel is fitted using a least-squares method so that it best reproduces the EPID-acquired image for a checkerboard field. The backscatter-correction method is implemented for a Varian Clinac equipped with a 40 cm x 30 cm (512 x 384 pixel) EPID and a Pinnacle³ TPS and tested for several rectangular and IMRT fields. The scatter, glare and energy-response correction kernel is implemented and tested for a simulated checkerboard field and a simulated IMRT field. Agreement between the EPID-measured image and TPS-calculated planar dose map is seen to improve from 6% to 2% when the backscatter region is added to the Pinnacle³ model. Agreement between the simulated EPID images and simulated TPS images is improved from 14% to approx. 1% when the radially-dependent kernel is used. Simultaneous application of both the backscatter region and Point-Spread Function is a promising direction for future investigations.</p> / Master of Science (MSc)

This research aims to develop a tissue-mimicking material and produce a 3D gelatin that has density of approximately a human lung, which is in the ranges of (0.25 – 0.35) g/cm3. Tissue equivalent models are important in order to study the radiation dose planned for patients. To achieve the desired density of a human tissue, different types of gelatin were whisked for 300 seconds using a typical hand mixer. The mechanical properties of the gelatin mixtures, standard and foamed, were evaluated by applying different forces. The mechanical properties for the gels were measured using an indentation technique, which showed that the gels act as elastic materials. The mechanical properties of the foams were also evaluated. Mixtures that contained 300 bloom gelatin, glycerol, and sorbitol, were whisked for 60, 180, 300 seconds to achieve different densities evaluated by CT imaging. The density of the180 - and 300 - seconds gelatin foams were found to be 0.33 ± 0.16 and 0.33  0.052 g/cm3, respectively, which is similar to the human lung density. Finally, FXO gel sheets and the FXO foam sheets were irradiated and the radiosensitivity quantified by measuring transmission using a spectrometer. The change in the attenuation coefficient was linear with dose. / Thesis / Master of Science (MSc)

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Diabetes epidemic is underway. Beta cell dysfunction (BCF) and loss of beta cell mass (BCM) are known to be key events in its progression. Currently, there are no reliable techniques to estimate or follow the loss of BCM, in vivo. Non-invasive imaging and quantification of the whole BCM in the pancreas, therefore, has a great potential for understanding the progression of diabetes and the scope for early diagnosis for Type 2 diabetes. Glucagon-like peptide-1 receptor (GLP-1R) is known to be selectively expressed on the pancreatic beta cells and overexpressed on the insulinoma, a pancreatic neuroendocrine tumor (PNET). Therefore, this receptor is considered to be a selective imaging biomarker for the beta cells and the insulinoma. Exendin-4 is a naturally occurring analog of GLP-1 peptide. It binds and activates GLP-1R with same the potency and engages in the insulin synthesis, with a longer biological half-life. In this thesis, Exendin-4 precursor, DO3A-VS-Cys40-Exendin-4 labeled with [68Ga], [68Ga]Ga-DO3A-VS-Cys40-Exendin-4 ([68Ga]Exendin-4), was evaluated in different species models, namely, immune deficient nude mice, rats, pigs, non-human primate (NHP), and clinically in one insulinoma patient by positron emission tomography (PET), for its potential in beta cell imaging and its quantification as well as for visualizing the insulinoma. From internal dosimetry, the possible number of repetitive [68Ga]Exendin-4-PET/CT scans was estimated. Pancreatic uptake and insulinoma tumor uptake of [68Ga]Exendin-4 were confirmed to be mediated by the specific binding to the GLP-1R. Pancreatic GLP-1R could be visualized and semi-quantified, for diabetic studies, except in rats. Nonetheless, we found conflicting results regarding the GLP-1R being a selective imaging biomarker for the beta cells. PET/CT scan of the patient with [68Ga]Exendin-4 has proven to be more sensitive than the clinical neuroendocrine tracer, [11C]5-HTP, as  it could reveal small metastatic tumors in liver. The kidney was the dose-limiting organ in the entire species model, from absorbed dose estimation. Before reaching a yearly kidney limiting dose of 150 mGy and a whole body effective dose of 10 mSv, 2–4 [68Ga]Exendin-4 PET/CT scans be performed in an adult human, which enables longitudinal clinical PET imaging studies of the GLP-1R in the pancreas, transplanted islets, or insulinoma, as well as in healthy volunteers enrolled in the early phase of anti-diabetic drug development studies.