NATALIA FIORINI DA SILVA

NATALIA FIORINI DA SILVA

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Interlaboratory comparison of two homemade pencil type ionization chambers
2024 - CASTRO, M.C.; SILVA, N.F.; CALDAS, L.V.E.
Computed tomography (CT) is a diagnostic exam responsible for the highest dose values received by the patients during the procedure. Over the years, this kind of equipment has been improved to ensure that the patients do not receive unnecessary doses. For this reason it is important to keep a quality control program for the CT equipment. To perform the dosimetry in CT beams, the instrument used is usually a pencil type ionization chamber with a sensitive volume length of 10 cm. However, this kind of detector is available with different sensitive volume lengths. The aim of this study was to compare the response of two homemade pencil type ionization chambers with sensitive volume lengths of 10 cm and 30 cm in the laboratories of Instituto de Pesquisas Energéticas e Nucleares (IPEN, Brazil) and National Physical Laboratory (NPL, UK). The characterization tests were performed, and the results obtained are within the international recommended limits. The only difference observed in the response of the two chambers in both laboratories is the fact that the ionization current obtained in all the tests at the IPEN is higher than at the NPL, because of the beam characteristics.
Performance comparison of an extrapolation chamber in computed tomography standard beams of two laboratories
2021 - CASTRO, MAYSA C.; SILVA, NATALIA F.; SANTOS, WILLIAM S.; CALDAS, LINDA V.E.
The doses received by the patients during the computed tomography (CT) exams are the highest when compared to other diagnostic radiology procedures. This fact makes it so important to keep the quality control using the correct instrument. For dosimetry in CT, a pencil type ionization chamber is usually utilized with a sensitive volume length of 10 cm. A comparison of the performance of an extrapolation chamber in two different laboratories, at the Instrument Calibration Laboratory (LCI) from Instituto de Pesquisas Energéticas e Nucleares (IPEN, Brazil) and at the National Physical Laboratory (NPL, UK) was undertaken. Two chamber characteristics were determined (zero depth and extrapolation curve), and the main recommended characterization tests were performed (stabilization time, saturation curve, polarity effect, ion collection efficiency, linearity of response, and variation of response with source-detector distance). This extrapolation chamber was calibrated using the standard system of NPL laboratory, and the energy dependence was determined. The results obtained were within the international recommendations of IEC 61674, except for the energy dependence, as already expected. This study also established a reference system for the LCI of the IPEN, using a homemade extrapolation chamber for X-ray CT beams. Using the extrapolation curves obtained in the characterization tests and the correction factors of ionic recombination, and scattering and fluorescence, the air kerma rates were obtained, as a reference system in standard laboratory computed tomography beams. The last correction factor was obtained using computer simulations by the MCNP5 code (Monte Carlo). Moreover, two pencil type ionization chambers were calibrated using the replacement method in relation to the extrapolation chamber.
Desenvolvimento e caracterização de um detector do tipo TH-GEM para metrologia das radiações ionizantes
2021 - SILVA, NATALIA F. da
O campo de detectores gasosos microestruturados representa atualmente um setor de tecnologias em crescimento dinâmico, entre as quais os detectores do tipo TH-GEM (THick Gas Electron Multiplier ) estão em destaque para uso em larga escala e aplicações generalizadas. As variações de detectores neste conceito têm sido utilizadas para dosimetria para diversos tipos de feixes de radiação e na produção de imagens. Com o intuito de contribuir com essa linha de pesquisa, o objetivo deste trabalho foi o desenvolvimento de um protótipo com características adequadas para metrologia das radiações ionizantes de baixas energias (feixes padronizados de mamografia). Este estudo foi pautado em simulações para otimização das condições de detecção e do detector, construção de um protótipo e na sua caracterização experimental. Determinou-se, por simulação de Monte Carlo, a influência de cada componente do detector do tipo TH-GEM na energia depositada no volume sensível, obtendo-se os valores de 0,09% para o invólucro, 0,01% para a placa coletora e 44% para a placa de amplificação. A espessura de 6 mm de alumínio para a blindagem foi obtida para uma eficiência de 99%. A placa de amplificação construída consiste em uma placa de circuito impresso perfurada em um padrão hexagonal, com orifícios de (0,254 ± 0,021) mm de diâmetro e (1,11 ± 0,12) mm de distância entre eles. A placa de amplificação foi submetida à caracterização elétrica onde foram obtidos os valores de (15,3 ± 0,4) GΩ para resistência e de (65,3 ± 1,7) pS para condutância. Para a caracterização experimental o detector do tipo TH-GEM foi preenchido com a mistura de Ar/CH4 na concentração 90/10. Foram obtidos experimentalmente valores para o ganho efetivo de 1,45 ± 0,10, 1,60 ± 0,10, 1,90 ± 0,12 e 2,20 ± 0,10 para as diferenças de potenciais aplicadas à placa de amplificação de 200 V, 300 V, 400 V e 450 V respectivamente. Além disso, foi possível verificar um comportamento linear da resposta do detector com a variação da corrente no tubo de raios X.
Dosimetric tests of an extrapolation chamber in standard computed tomography beams
2021 - CASTRO, M.C.; SILVA, N.F.; CALDAS, L.V.E.
Computed tomography (CT) diagnostic exams are responsible for the highest dose values to the patients. There-fore, the radiation doses in this procedure must be accurate. For the dosimetry of CT beams, the radiation detec-tor is usually a pencil-type ionization chamber. This type of dosimeter presents a uniform response to the inci-dent radiation beam from all angles, which makes it suitable for such equipment since the X-ray tube executes a circular movement around the table during irradiation. However, there is no primary standard system for this kind of radiation beam yet. In order to search for a CT primary standard, an extrapolation chamber built at the Calibration Laboratory (LCI) of the Instituto de Pesquisas Energéticas e Nucleares (IPEN) was tested. An ex-trapolation chamber is a parallel-plate ionization chamber that allows the variation of its sensitive air volume. This chamber was used previously for low-energy radiation beams and showed results within the international recommended limits. The aim of this work is to perform some characterization tests (saturation curve, polarity effect, ion collection efficiency and linearity of response) considering the chamber depth of 1.25 mm in the radia-tion qualities for computed tomography beams at the LCI. The results showed to be within the international recommended limits.
Performance of an extrapolation chamber in computed tomography standard beams
2021 - CASTRO, MAYSA C.; SILVA, NATALIA F.; CALDAS, LINDA V.E.
Among the medical uses of ionizing radiations, the computed tomography (CT) diagnostic exams are responsible for the highest dose values to the patients. The dosimetry procedure in CT scanner beams makes use of pencil ionization chambers with sensitive volume lengths of 10 cm. The aim of its calibration is to compare the values that are obtained with the instrument to be calibrated and a standard reference system. However, there is no primary standard system for this kind of radiation beam. Therefore, an extrapolation ionization chamber, built at the Calibration Laboratory (LCI), was used to establish a CT primary standard. The objective of this work was to perform some characterization tests (short- and medium-term stabilities, saturation curve, polarity effect and ion collection efficiency) in the standard X-ray beams established for computed tomography at the LCI.
Garfield++ simulation of a TH-GEM based detector for standard mammography beam dosimetry
2021 - SILVA, NATALIA F.; SILVA, TIAGO F.; CASTRO, MAYSA C.; LUZ, HUGO N. da; CALDAS, LINDA V.E.
The TH-GEM based detector is a robust, simple to manufacture, high-gain gaseous electron multiplier. Its operation is based on a standard printed circuit board (PCB) coated on both sides by metallic material, perforated in a millimeter pattern, and immersed in gas. In order to study the feasibility of using TH-GEM type detectors in dosimetric applications for standard mammography beams, a prototype with adequate dimensions and materials was produced. The present work encompasses the calculations of electric fields by the Gmsh and Elmer software packages and the avalanche simulation using Garfield++ library of a TH-GEM detector filled with Ar/CO2 mixture at atmospheric pressure.
Some characterization tests for an extrapolation chamber in CT standard beams in a specific chamber depth
2020 - CASTRO, M.C.; SILVA, N.F.; CALDAS, L.V.E.
Among all diagnostic exams, the computed tomography (CT) is responsible for the highest dose values to the patients. So, the radiation doses in this procedure must be accurate for the dosimetry procedure in CT scanner beams making use of pencil ionization chambers with sensitive volume lengths of 10 cm. However, there is no primary standard system for this kind of radiation beam. An extrapolation ionization chamber, built at the Cali-bration Laboratory (LCI) was tested to establish a CT primary standard. The aim of this work was to perform some characterization tests (short- and medium-term stabilities, energy dependence, angular dependence) in the standard X-ray beams established for computed tomography at the LCI in a specific chamber depth (1.25 mm). The results showed to be within the international recommended limits except for the energy dependence.
Evaluation of an extrapolation chamber for dosimetry in computed tomography beams using Monte Carlo code (MCNP5)
2020 - CASTRO, MAYSA C.; SILVA, NATALIA F.; SANTOS, LUCAS R.; CINTRA, FELIPE B.; CALDAS, LINDA V.E.
Computed tomography (CT) is responsible for the highest dose values to the patients during the exams. Therefore, the radiation doses in this procedure must be accurate. However, there is no primary standard system for this kind of radiation beam yet. A homemade extrapolation ionization chamber was preliminary evaluated for the establishment of a CT beam primary standard. The aim of this study was to determine the influence that the various components of the extrapolation chamber may present on the energy deposited in its sensitive volume. Different materials for its collecting electrode were also studied for this type of radiation beam. The evaluation of the homemade extrapolation chamber showed the highest influence of 25.9% for the collecting electrode, and the best material for the collecting electrode for CT radiation beams was graphite.
Garfield++ simulation of a TH-GEM based detector for standard mammography beam dosimetry
2019 - SILVA, N.F.; SILVA, T.F.; CASTRO, M.C.; LUZ, H.N. da; CALDAS, LINDA V.E.
The TH-GEM based detector is a robust, simple to manufacture, high-gain gaseous electron multiplier. Its operation is based on a standard printed circuit board (PCB) coated on both sides by metallic material, perforated in a millimeter pattern, and immersed in gas. In order to study the feasibility of using TH-GEM type detectors in dosimetric applications for standard mammography beams, a prototype with adequate dimensions and materials was produced. The present work encompasses the calculations of electric fields by the Gmsh and Elmer software packages and the avalanche simulation using Garfield++ library of a TH-GEM detector filled with Ar/CO2 (70:30) mixture at atmospheric pressure.
Dosimetric tests of an extrapolation chamber in standard computed tomography beams
2019 - CASTRO, MAYSA C. de; SILVA, NATALIA F. da; CALDAS, LINDA V. E.
Computed tomography (CT) diagnostic exams are responsible for the highest dose values to the patients. Therefore, the radiation doses in this procedure must be accurate. For the dosimetry of CT beams, the radiation detector is usually a pencil-type ionization chamber. This type of dosimeter presents a uniform response to the incident radiation beam from all angles, which makes it suitable for such equipment since the X-ray tube executes a circular movement around the table during irradiation. However, there is no primary standard system for this kind of radiation beam yet. In order to search for a CT primary standard, an extrapolation chamber built at the Calibration Laboratory (LCI) of the Instituto de Pesquisas Energéticas e Nucleares (IPEN) was tested. An extrapolation chamber is a parallel-plate ionization chamber that allows the variation of its sensitive air volume. This chamber was used previously for low-energy radiation beams and showed results within the international recommended limits. The aim of this work is to perform some characterization tests (saturation curve, polarity effect, ion collection efficiency and linearity of response) considering the chamber depth of 1.25 mm in the radiation qualities for computed tomography beams at the LCI. The results showed to be within the international recommended limits.