RESUMO
This work aims to evaluate the potential risks of incidents in nuclear research reactors. For its development, two databases of the International Atomic Energy Agency (IAEA) were used: the Research Reactor Data Base (RRDB) and the Incident Report System for Research Reactor (IRSRR). For this study, the probabilistic safety analysis (PSA) was used. To obtain the result of the probability calculations for PSA, the theory and equations in the paper IAEA TECDOC-636 were used. A specific program to analyse the probabilities was developed within the main program, Scilab 5.1.1. for two distributions, Fischer and chi-square, both with the confidence level of 90 %. Using Sordi equations, the maximum admissible doses to compare with the risk limits established by the International Commission on Radiological Protection (ICRP) were obtained. All results achieved with this probability analysis led to the conclusion that the incidents which occurred had radiation doses within the stochastic effects reference interval established by the ICRP-64.
Assuntos
Centrais Elétricas , Proteção Radiológica , Liberação Nociva de Radioativos , Gestão da Segurança , Humanos , Energia Nuclear , Probabilidade , Monitoramento de RadiaçãoRESUMO
PURPOSE: The intra-arterial administration of radioactive glass microspheres is an alternative therapy option for treating primary hepatocellular carcinoma, the main cause of liver cancer death, and metastatic liver cancer, another important kind of cancer induced in the liver. The technique involves the administration of radioactive microspheres in the hepatic artery, which are trapped preferentially in the tumor. METHODS: In this work the GEANT4 toolkit was used to calculate the radial dose-rate distributions in water from 32P-loaded glass microspheres and also from 90Y-loaded glass microspheres. To validate the toolkit for this application, the authors compared the dose-rate distribution of 32P and 90Y point sources in water with data from the International Commission on Radiation Units and Measurements report 72. RESULTS: Tables of radial dose-rate distributions are provided for practical use in brachytherapy planning with these microspheres. CONCLUSIONS: The simulations with the microspheres show that the shape of the beta ray energy spectra with respect to the 32P and 90Y sources is significantly modified by the glass matrix.
Assuntos
Artérias , Braquiterapia/instrumentação , Braquiterapia/métodos , Radioisótopos de Fósforo/análise , Radioisótopos de Fósforo/uso terapêutico , Próteses e Implantes , Planejamento da Radioterapia Assistida por Computador/métodos , Simulação por Computador , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Vidro , Humanos , Microesferas , Modelos Teóricos , Doses de Radiação , Dosagem Radioterapêutica , Reprodutibilidade dos Testes , Espalhamento de Radiação , Sensibilidade e EspecificidadeRESUMO
PURPOSE: Radiopharmaceutical applications in nuclear medicine require a detailed dosimetry estimate of the radiation energy delivered to the human tissues. Over the past years, several publications addressed the problem of internal dose estimate in volumes of several sizes considering photon and electron sources. Most of them used Monte Carlo radiation transport codes. Despite the widespread use of these codes due to the variety of resources and potentials they offered to carry out dose calculations, several aspects like physical models, cross sections, and numerical approximations used in the simulations still remain an object of study. Accurate dose estimate depends on the correct selection of a set of simulation options that should be carefully chosen. This article presents an analysis of several simulation options provided by two of the most used codes worldwide: MCNP and GEANT4. METHODS: For this purpose, comparisons of absorbed fraction estimates obtained with different physical models, cross sections, and numerical approximations are presented for spheres of several sizes and composed as five different biological tissues. RESULTS: Considerable discrepancies have been found in some cases not only between the different codes but also between different cross sections and algorithms in the same code. Maximum differences found between the two codes are 5.0% and 10%, respectively, for photons and electrons. CONCLUSION: Even for simple problems as spheres and uniform radiation sources, the set of parameters chosen by any Monte Carlo code significantly affects the final results of a simulation, demonstrating the importance of the correct choice of parameters in the simulation.