Quantitative Evaluation of Scintillation Camera Imaging Characteristics of Isotopes Used in Liver Radioembolization

Scintillation camera imaging is used for treatment planning and post-treatment dosimetry in liver radioembolization (RE). In yttrium-90 (90Y) RE, scintigraphic images of technetium-99m (99mTc) are used for treatment planning, while 90Y Bremsstrahlung images are used for post-treatment dosimetry. In holmium-166 (166Ho) RE, scintigraphic images of 166Ho can be used for both treatment planning and post-treatment dosimetry. The aim of this study is to quantitatively evaluate and compare the imaging characteristics of these three isotopes, in order that imaging protocols can be optimized and RE studies with varying isotopes can be compared.Phantom experiments were performed in line with NEMA guidelines to assess the spatial resolution, sensitivity, count rate linearity, and contrast recovery of 99mTc, 90Y and 166Ho. In addition, Monte Carlo simulations were performed to obtain detailed information about the history of detected photons. The results showed that the use of a broad energy window and the high-energy collimator gave optimal combination of sensitivity, spatial resolution, and primary photon fraction for 90Y Bremsstrahlung imaging, although differences with the medium-energy collimator were small. For 166Ho, the high-energy collimator also slightly outperformed the medium-energy collimator. In comparison with 99mTc, the image quality of both 90Y and 166Ho is degraded by a lower spatial resolution, a lower sensitivity, and larger scatter and collimator penetration fractions.The quantitative evaluation of the scintillation camera characteristics presented in this study helps to optimize acquisition parameters and supports future analysis of clinical comparisons between RE studies

Retrospective evaluation of bone pain palliation after samarium-153-EDTMP therapy Avaliação retrospectiva do tratamento da dor óssea metastática com Samário-153-EDTMP

PURPOSE: The aim of this study was to evaluate the degree of metastatic bone pain palliation and medullar toxicity associated with samarium-153-EDTMP treatment. METHODS: Seventy-three patients with metastatic bone pain having previously undergone therapy with samarium-153-EDTMP (1 mCi/kg) were retrospectively evaluated. Routine follow-up included pain evaluation and blood counts for 2 months after treatment. Pain was evaluated using a subjective scale (from 0 to 10) before and for 8 weeks after the treatment. Blood counts were obtained before treatment and once a week for 2 months during follow-up. Dosimetry, based upon the urinary excretion of the isotope, was estimated in 41 individuals, and the resulting radiation absorbed doses were correlated with hematological data. RESULTS: Reduction in pain scores of 75% to 100% was obtained in 36 patients (49%), with a decrease of 50% to 75%, 25% to 50%, and 0% to 25% in, respectively, 20 (27%), 10 (14%), and 7 (10%) patients. There was no significant relationship between the pain response and location of the primary tumor (breast or prostate cancer). Mild to moderate myelosuppression was noted in 75.3% of patients, usually with hematological recovery at 8 weeks. The mean bone marrow dose was 347 ± 65 cGy, and only a weak correlation was found between absorbed dose and myelosuppression (Pearson coefficient = .4). CONCLUSIONS: Samarium-153-EDTMP is a valuable method for metastatic bone pain palliation. A mild to moderate and transitory myelosuppression is the main toxicity observed after samarium therapy, showing a weak correlation with dosimetric measures.<br>OBJETIVO: O presente trabalho teve por objetivo avaliar o efeito paliativo da dor e a toxicidade medular associados ao tratamento com Samário-153-EDTMP em pacientes com metástases ósseas. MÉTODOS: O estudo foi realizado de forma retrospectiva, a partir do levantamento de prontuário de 178 pacientes submetidos a tratamento com 1mCi/kg de 153Sm-EDTMP devido à dor por metástases ósseas. Os prontuários de 73 pacientes foram considerados adequados para análise dos parâmetros clínicos (intensidade da dor) e laboratoriais (hemograma). A intensidade da dor foi avaliada em escala de 0 a 10 pelo próprio paciente, antes e durante 8 semanas após o tratamento. Hemograma completo foi realizado antes do tratamento e a cada semana nas 8 semanas seguintes. Estudos de dosimetria foram realizados em 41 dos 73 pacientes, baseados na excreção urinária e retenção do radioisótopo, sendo a dose de radiação absorvida correlacionada à toxicidade medular. RESULTADOS: Redução importante na intensidade da dor (diminuição de 75 a 100% do basal) foi constatada em 36 pacientes (49%), com redução de 50-75%, 25-50% e 0-25% em, respectivamente, 20 (27%), 10 (14%) e 7 (10%) casos. Não se observou variação significativa da resposta entre os pacientes com tumor primário de mama (n=29) ou de próstata (n=36). Toxicidade medular foi observada em 75,3% dos pacientes (71,2% com leucopenia e 53,4% com plaquetopenia), em geral de grau leve a moderado e com recuperação ao término da 8º semana. A dose média de medula foi de 347±65 cGy, havendo baixa correlação entre a dosimetria medular e a queda da contagem de leucócitos (coeficiente de correlação linear de 0,40) ou de plaquetas (coeficiente de correlação linear = 0,48). CONCLUSÕES: O tratamento com Samário-153-EDTMP permitiu um adequado controle da dor por metástases ósseas, com significativa redução na intensidade da dor. A toxicidade medular transitória foi a principal reação adversa observada, em geral de grau leve a moderado, apresentando baixa correlação com as medidas dosimétricas