Sucrose hydrolysis by invertase using a membrane reactor: effect of membrane cut-off on enzyme performance

Sucrose hydrolysis by invertase [EC.3.2.1.26] produces inverted sugar syrup, an ingredient mainly used in the food industry. To properly catalyze hydrolysis, the enzyme should be reused after this reaction. It is advisable to maintain constant activity over a considerable period. Thus, sucrose hydrolysis was performed in a membrane bioreactor - a continuously stirred tank reactor coupled with an ultrafiltration membrane (UFM) which provides good diffusion and high activity per unit volume. Molecular weight cut-off for soluble invertase UFMs was up to 100kDa. This study focused on the role of UFM invertase cut-off as it is the main element in the process. We demonstrated that both the cut-off and chemical nature of the UFM affected specific invertase activity

Comparison of I-131 Radioimmunotherapy Tumor Dosimetry: Unit Density Sphere Model Versus Patient-Specific Monte Carlo Calculations

High computational requirements restrict the use of Monte Carlo algorithms for dose estimation in a clinical setting, despite the fact that they are considered more accurate than traditional methods. The goal of this study was to compare mean tumor absorbed dose estimates using the unit density sphere model incorporated in OLINDA with previously reported dose estimates from Monte Carlo simulations using the dose planning method (DPMMC) particle transport algorithm. The dataset (57 tumors, 19 lymphoma patients who underwent SPECT/CT imaging during I-131 radioimmunotherapy) included tumors of varying size, shape, and contrast. OLINDA calculations were first carried out using the baseline tumor volume and residence time from SPECT/CT imaging during 6 days post-tracer and 8 days post-therapy. Next, the OLINDA calculation was split over multiple time periods and summed to get the total dose, which accounted for the changes in tumor size. Results from the second calculation were compared with results determined by coupling SPECT/CT images with DPM Monte Carlo algorithms. Results from the OLINDA calculation accounting for changes in tumor size were almost always higher (median 22%, range -1%-68%) than the results from OLINDA using the baseline tumor volume because of tumor shrinkage. There was good agreement (median -5%, range -13%-2%) between the OLINDA results and the self-dose component from Monte Carlo calculations, indicating that tumor shape effects are a minor source of error when using the sphere model. However, because the sphere model ignores cross-irradiation, the OLINDA calculation significantly underestimated (median 14%, range 2%-31%) the total tumor absorbed dose compared with Monte Carlo. These results show that when the quantity of interest is the mean tumor absorbed dose, the unit density sphere model is a practical alternative to Monte Carlo for some applications. For applications requiring higher accuracy, computer-intensive Monte Carlo calculation is needed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90433/1/cbr-2E2011-2E0965.pd

Uso do código MCNP-4C para análise da curva de PDP em feixes de fótons de alta energia

Introdução: O método de Monte Carlo tem sido largamente aplicado para simulações de tratamentos e modelagem de feixes de radiação utilizados em radioterapia. As simulações envolvem características específicas do problema: geometria; composição; disposição dos elementos da simulação; especificações da fonte. Nestas simulações, um desafio é determinar o espectro da fonte de radiação, pois os fabricantes dos equipamentos não disponibilizam as informações específicas do feixe. O espectro pode ser obtido por um método empírico a partir da curva experimental de Porcentagem de Dose Profunda (PDP) e perfil de planura, obtidos nos procedimentos de dosimetria. Objetivos: Reconstruir as PDP experimentais dos feixes de 6 MV e 10 MV do acelerador linear Varian, modelo 2100C, através de simulações com o código MCNP-4C. Métodos: Os valores experimentais da PDP foram cedidos pelo Setor de Radioterapia do Hospital das Clínicas da UNESP de Botucatu. O MCNP-4C foi utilizado para simulações e reconstrução da curva de PDP. A modelagem geométrica considerou uma fonte plana de fótons, a 100cm da superfície de um fantoma cúbico de água contendo, em seu interior, 31 elipsoides (uma a cada 1cm). A energia depositada foi calculada para cada elipsoide e, com esses resultados, foram reconstruídas as curvas de PDP. Resultados: O desvio máximo encontrado para cada ponto foi de 1%, comprovando a consistência das medidas obtidas pelo MCNP-4C. A diferença máxima entre curvas experimentais e simuladas foi de 3,7% (feixe 6MV) e 4,6% (10MV). Conclusão: A concordância entre os resultados, para os feixes de fótons, valida a metodologia proposta

Sucrose hydrolysis by invertase using a membrane reactor: effect of membrane cut-off on enzyme performance

Sucrose hydrolysis by invertase [EC.3.2.1.26] produces inverted sugar syrup, an ingredient mainly used in the food industry. To properly catalyze hydrolysis, the enzyme should be reused after this reaction. It is advisable to maintain constant activity over a considerable period. Thus, sucrose hydrolysis was performed in a membrane bioreactor - a continuously stirred tank reactor coupled with an ultrafiltration membrane (UFM) which provides good diffusion and high activity per unit volume. Molecular weight cut-off for soluble invertase UFMs was up to 100kDa. This study focused on the role of UFM invertase cut-off as it is the main element in the process. We demonstrated that both the cut-off and chemical nature of the UFM affected specific invertase activity