Avaliação das doses de radiação X em exames pediátricos de tomografia computadorizada de cranio com base em estudos de otimização
Nenhuma Miniatura disponível
Data
2005
Autores
Daros, Kellen Adriana Curci [UNIFESP]
Orientadores
Medeiros, Regina Bitelli [UNIFESP]
Tipo
Tese de doutorado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Objetivo: identificar condições técnicas para exames de TC de crânio que ofereçam menor dose absorvida e que atendam as recomendações do fabricante quanto à resolução espacial. Avaliar a dose absorvida em exames de TC de crânio em crianças de até 6 anos na condição técnica sugerida pelo fabricante e em condições clínicas de rotina. Estabelecer uma relação quantitativa entre a dose absorvida e sua distribuição nas regiões do crânio de pacientes pediátricos de até 6 anos de idade de modo a estimar as doses em condições otimizadas. Métodos: foram medidas as doses de radiação X na superfície do crânio de 64 pacientes pediátricos em exames de tomografia realizados com o equipamento Tomoscan AV-Philips, utilizando 40 dosímetros termoluminescentes do tipo TLD100. Os dados dosimétricos geraram informações para determinação da distribuição de dose ao longo do crânio. A condição de exposição (CE) indicada pelo fabricante foi de 120 kV e 450 mAs e a indicada pela equipe clínica foi de 120 kV com 75 a 175 mAs. Com o simulador de teste de qualidade da imagem, modelo Phantom C-Philips, foram avaliados os níveis de ruído decorrentes de imagens geradas com tensões de 100 a 140 kV entre 50 e 800 mAs. Simultaneamente à aquisição das imagens, as doses absorvidas foram medidas na superfície do simulador para cada mAs com a câmara de ionização tipo lápis modelo 660-6-Victoreen. Destas medidas foi possível determinar a relação gráfica entre o ruído da imagem e a dose absorvida relativa em função de diferentes mAs para diferentes tensões no tubo (kV). As CEs que geraram imagens com doses menores e níveis de ruídos aceitáveis foram comparados com a imagem de referência indicada pelo fabricante, permitindo a seleção de técnicas otimizadas que foram avaliadas em termos de resolução espacial de alto e baixo contraste, utilizando-se o mesmo simulador. Resultados: A CE que gerou menor dose e qualidade de imagem aceitável foi de 120 kV, filtro 2, matriz 512x512 pixels com 300 mAs, para cortes de 3 mm de espessura e 200 mAs para cortes de 7mm de espessura. Nesta condição houve uma redução da dose absorvida de 34,4 por cento para as exposições do crânio aos raios-X secundários e 33,5 por cento aos primários em relação à dose gerada na CE sugerida pelo fabricante do tomágrafo que foi estimada em 169,7(50,2) cGy. Conclusão: É possível reduzir a dose efetiva no exame de TC a partir do estudo de técnicas otimizadas. A condição operacional proposta pela equipe clínica promoveu uma redução na dose total de 84,1 por cento em relação à condição operacional proposta pelo fabricante, porém gerou perdas de qualidade relacionadas à resolução de alto e baixo contraste, inaceitáveis. O uso da dosimetria termoluminescente possibilitou a determinação da distribuição da dose absorvida no paciente de forma integrada para as diferentes condições de exposição aos raios-X presentes no exame
Purpose: To identify technical conditions for head CT exams that offer low absorbed dose and attended the manufacturer's recommendations about spatial resolutions. To evaluate the absorbed dose in head CT exams in children until 6 years old under the technical conditions suggested by the manufacturer and under the routine clinicai conditions. To establish a quantitative relation between the absorbed dose and its distributions on the head regions of the pediatric patients until 6 years old, in order to estimate the doses in optimizing conditions. Methods: The doses of X radiation on the head surface were measured in 64 pediatric patients in tomography exams made with the Tomoscan AV-Philips, using 40 termoluminescent dosimeters TLD 100 type.The dosimetry has generated information for the determination of the doses distribution ali over the head. The exposing conditions (CE) indicated by the manufacturer were 120 kV and 450 mAs and the one indicated by the clinicai team was 120 kV with 75 to 175 mAs. With the quality of image test phantom, model Phantom C-Philips, the levei of noise decurrently from the images created with potential tube from 100 to 140 kV, between 50 and 800 mAs was measured. Simultaneously to the acquisition of the images, the absorbed doses were measured on the phantom surface to each mAs, with the ionization chamber model 660-6-Victoreen. From these measures, it was possible to determinate the graphic relation between the image noise and the reiative absorbed dose in function of different mAs to different potentials on the tube (kV). The CEs that generated images with lower doses and acceptable leveis of noise were compared to the reference image indicated by the manufactúrer, allowing the selection of optimized techniques that were evaluated in terms of spatial resolution of high and low contrast, using the same phantom. Results: The CE that has generated smallest dose and acceptable image quality was 120 kV, filter 2, matrix 512x512 pixels with 300 mAs, for slices thickness of 3 mm and 200 mAs for slice thickness of 7 mm of. In this condition, ' there was a reduction of the absorbed dose of 32,3% for the head exposure to the secondary X-rays and 33,5% to the primary in relation to the generated dose on CE suggested by the scanner manufacturer, which was estimated in 169,7(50,2) cGy. Conclusion: It is possible to reduce the effective dose on the CT exam from the studies of optimized techniques. The operatiorial condition proposed by the clinicai team promoted a reduction of 84,1% on the total dose in relation to the operational condition proposed by the manufacturer, however, it has generated unacceptable losses of quality related to the resolutions of high and low contrast. The utilization of termoluminescent dosimetry made the determination of the distribution of the absorbed dose on the patient possible in an integrated way for the difterent conditions of exposure to the X-rays contained in the examinations
Purpose: To identify technical conditions for head CT exams that offer low absorbed dose and attended the manufacturer's recommendations about spatial resolutions. To evaluate the absorbed dose in head CT exams in children until 6 years old under the technical conditions suggested by the manufacturer and under the routine clinicai conditions. To establish a quantitative relation between the absorbed dose and its distributions on the head regions of the pediatric patients until 6 years old, in order to estimate the doses in optimizing conditions. Methods: The doses of X radiation on the head surface were measured in 64 pediatric patients in tomography exams made with the Tomoscan AV-Philips, using 40 termoluminescent dosimeters TLD 100 type.The dosimetry has generated information for the determination of the doses distribution ali over the head. The exposing conditions (CE) indicated by the manufacturer were 120 kV and 450 mAs and the one indicated by the clinicai team was 120 kV with 75 to 175 mAs. With the quality of image test phantom, model Phantom C-Philips, the levei of noise decurrently from the images created with potential tube from 100 to 140 kV, between 50 and 800 mAs was measured. Simultaneously to the acquisition of the images, the absorbed doses were measured on the phantom surface to each mAs, with the ionization chamber model 660-6-Victoreen. From these measures, it was possible to determinate the graphic relation between the image noise and the reiative absorbed dose in function of different mAs to different potentials on the tube (kV). The CEs that generated images with lower doses and acceptable leveis of noise were compared to the reference image indicated by the manufactúrer, allowing the selection of optimized techniques that were evaluated in terms of spatial resolution of high and low contrast, using the same phantom. Results: The CE that has generated smallest dose and acceptable image quality was 120 kV, filter 2, matrix 512x512 pixels with 300 mAs, for slices thickness of 3 mm and 200 mAs for slice thickness of 7 mm of. In this condition, ' there was a reduction of the absorbed dose of 32,3% for the head exposure to the secondary X-rays and 33,5% to the primary in relation to the generated dose on CE suggested by the scanner manufacturer, which was estimated in 169,7(50,2) cGy. Conclusion: It is possible to reduce the effective dose on the CT exam from the studies of optimized techniques. The operatiorial condition proposed by the clinicai team promoted a reduction of 84,1% on the total dose in relation to the operational condition proposed by the manufacturer, however, it has generated unacceptable losses of quality related to the resolutions of high and low contrast. The utilization of termoluminescent dosimetry made the determination of the distribution of the absorbed dose on the patient possible in an integrated way for the difterent conditions of exposure to the X-rays contained in the examinations
Descrição
Citação
São Paulo: [s.n.], 2005. 119 p.