Introdução: A avaliação da distribuição de material radioativo na articulação por imagens SPECT pós radiosinoviortese (RSO) com ítrio-90 ( 90 Y) visa garantir a eficácia e segurança da terapia. Contudo, a qualidade de imagem por Bremsstrahlung possui grandes limitações, tornando necessários estudos sobre a otimização de parâmetros de aquisição SPECT e dos métodos de reconstrução de imagem para o radionuclídeo 90 Y. Métodos: Foram obtidas imagens SPECT de um simulador de acrílico contendo quatro inserções cilíndricas de diferentes diâmetros que mimetizam lesões captantes, com colimadores de alta, média e baixa (HEGP, MEGP e LEHR) energia, janela de energia de 130 keV, largura 70% e matriz 64 x 64. Os métodos de reconstrução utilizados foram FBP e OSEM, com aplicação de diferentes filtros e número de iterações. Resultados: O maior contraste de imagem foi observado para o método de reconstrução iterativo, com a aplicação do filtro Gauss, sendo que o método FBP apresentou resultados insatisfatórios. O acréscimo no número de iterações no método OSEM não apresentou aumento da qualidade da imagem. Há menor discrepância entre os valores de captação das diferentes lesões para as aquisições com o colimador HEGP. Conclusões: Há diferença significativa na quantificação entre as reconstruções FBP e OSEM. O uso do colimador HEGP e do método de reconstrução iterativo OSEM com a aplicação do filtro Gauss se mostrou como o protocolo de aquisição de imagem mais indicado para estudos com 90 Y.
This work aims to compare SPECT (Single Photon Emission Tomography Computed) and planar modalities as the most efficient methodology to perform dosimetry by molecular imaging. Twenty-one male C57BL6 mice induced with murine melanoma cell line B16-F10, administered 131I-Ixolaris were used for melanoma therapy. The procedures applied to them followed the standards described for the use of experimental animals, duly approved by the National Council for Animal Experimentation Control (CONCEA from Federal University of Rio de Janeiro. The accumulated activities were obtained in order to estimate the absorbed doses in each organ. Mass and metabolic differences between mice and humans were considered and used to extrapolate data acquired at different scales. From the dose factors provided by the MIRDOSE software, the absorbed doses in the target organs irradiated by the source organs were calculated and, finally, the effective dose was estimated. From the Student's t-hypothesis test performed in the accumulated activity, absorbed dose and S-factor quantities, there is no statistically significant difference between performing the image dosimetry from SPECT and planar acquired images.
This study aimed to determine the biokinetic model for Ixolaris labelled with 99mTc radiotracer in mice by means of an imaging dosimetry method to estimate the absorbed and effective doses resulting from the diagnosis of melanoma and metastases in humans. C57BL6 mice induced animals with cell line B16-F10 murine melanoma were tested. It was determined by Single Photon Emission Tomography Computed (SPECT) images a latency period of 15 to 21 days for the development of lung metastasis in mice. The 99mTc-Ixolaris radiopharmaceutical was intravenously administered in a caudal vein, and SPECT images were acquired approximately at 0.5 h, 1.5 h, 2.5 h, 3.5 h and 24 h post-administration for analysis and biodistribution quantification. The biokinetic model was determined and cumulative activity to estimate the absorbed dose in each organ was calculated. The mass and metabolic differences between mice and humans were considered and used to extrapolate the data for different scales. Absorbed doses in irradiated target organs were calculated for the source organs based on dose factors provided by the software MIRDOSE and Olinda/EXM (S factor). Afterwards, the effective doses were estimated. The metabolic differences were 7,02 in this study. The dosimetric results indicated an estimated effective dose of 4.3 mSv for diagnostic exams conducted in human melanoma patients for an administered activity of 25.7 MBq. Comparing with effective doses resulting from other 99mTc diagnostic techniques, effective dose ranging from 0.6 to 4.8 mSv it was concluded that the procedure should proceed into a Clinical Phase in humans.
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