RESUMO
The aim of this study was the calculation of conversion coefficients for absorbed doses per fluence (DT/Φ) using the sitting and standing male hybrid phantom (UFH/NCI) exposure to monoenergetic protons with energy ranging from 2 MeV to 10 GeV. Sex-averaged effective dose per fluence (E/Φ) using the results of DT/Φ for the male and female hybrid phantom in standing and sitting postures were also calculated. Results of E/Φ of UFH/NCI standing phantom were also compared with tabulated effective dose conversion coefficients provided in ICRP publication 116. To develop an exposure scenario implementing the male UFH/NCI phantom in sitting and standing postures was used the radiation transport code MCNPX. Whole-body irradiations were performed using the recommended irradiation geometries by ICRP publication 116 antero-posterior (AP), postero-anterior (PA), right and left lateral, rotational (ROT) and isotropic (ISO). In most organs, the conversion coefficients DT/Φ were similar for both postures. However, relative differences were significant for organs located in the lower abdominal region, such as prostate, testes and urinary bladder, especially in the AP geometry. Results of effective dose conversion coefficients were 18% higher in the standing posture of the UFH/NCI phantom, especially below 100 MeV in AP and PA. In lateral geometry, the conversion coefficients values below 20 MeV were 16% higher in the sitting posture. In ROT geometry, the differences were below 10%, for almost all energies. In ISO geometry, the differences in E/Φ were negligible. The results of E/Φ of UFH/NCI phantom were in general below the results of the conversion coefficients provided in ICRP publication 116.
Assuntos
Imagens de Fantasmas , Prótons , Doses de Radiação , Irradiação Corporal Total , Feminino , Humanos , Masculino , Método de Monte Carlo , Neoplasias/radioterapia , Postura , Proteção RadiológicaRESUMO
Absorbed fraction (AF) calculations to the human skeletal tissues due to alpha particles are of interest to the internal dosimetry of occupationally exposed workers and members of the public. The transport of alpha particles through the skeletal tissue is complicated by the detailed and complex microscopic histology of the skeleton. In this study, both Monte Carlo and chord-based techniques were applied to the transport of alpha particles through 3-D microCT images of the skeletal microstructure of trabecular spongiosa. The Monte Carlo program used was 'Visual Monte Carlo--VMC'. VMC simulates the emission of the alpha particles and their subsequent energy deposition track. The second method applied to alpha transport is the chord-based technique, which randomly generates chord lengths across bone trabeculae and the marrow cavities via alternate and uniform sampling of their cumulative density functions. This paper compares the AF of energy to two radiosensitive skeletal tissues, active marrow and shallow active marrow, obtained with these two techniques.
Assuntos
Osso e Ossos/fisiologia , Modelos Biológicos , Contagem Corporal Total/métodos , Partículas alfa , Bioensaio/métodos , Simulação por Computador , Humanos , Internacionalidade , Cinética , Método de Monte Carlo , Especificidade de Órgãos , Doses de Radiação , Eficiência Biológica Relativa , Sensibilidade e Especificidade , Especificidade da Espécie , Distribuição TecidualRESUMO
In May 2000, an operator of a (60)Co industrial gamma radiography apparatus, during a routine service, was involved in a partial-body radiological accident, which caused serious injuries to his left hand. Dose reconstruction was started aiming to assess the radiation doses, in order to assist the medical staff in the evaluation and prescription of suitable medical procedures for the patient's treatment and follow-up. This work presents the dose reconstruction used for assessment of the distribution of doses on the patient's left hand, which was made using two methods: physical and computational techniques. For the first technique a physical hand simulator was built. The computational method was performed using microcomputer software for external dose calculations, named 'Visual Monte-Carlo-VMC', together with a hand voxel simulator. The values obtained through both methods for the distribution of absorbed doses on the operator's left hand were compared. About half of them were similar within a range of uncertainty of 20%.
Assuntos
Radioisótopos de Cobalto/efeitos adversos , Mãos/efeitos da radiação , Exposição Ocupacional/efeitos adversos , Liberação Nociva de Radioativos , Radiometria/métodos , Adulto , Brasil , Humanos , Masculino , Método de Monte Carlo , Doses de RadiaçãoRESUMO
Radionuclides deposited internally in the mother will give rise to a radiation dose in the infant in two ways. The radionuclides may be transferred through milk and give rise to an internal dose in the infant, or the radionuclides may emit photons that are absorbed by the infant, giving rise to an external dose. In this paper, the external dose to the newborn infant caused by direct irradiation was estimated for monoenergetic photons. Voxel models (also called voxel phantoms) of the mother and infant were made in three geometries. These models, consisting of volume elements, or voxels, were designed so that the infant model was placed in the lap, at the breast and on the shoulder of the mother model. The Visual Monte Carlo (VMC) code was used to transport the photons through the voxel models. Source regions for the emitted photons, such as the whole body, the thyroid, the lung, the liver and the skeleton, were chosen. For the validation of the calculation procedure, VMC results were favourably compared with the results obtained by using other Monte Carlo programs and also with the previously published results for specific absorbed fractions. This paper provides estimates of the external dose per photon to the infant for photon energies between 0.05 and 2.5 MeV. The external dose per photon estimates were made for the three geometries and for the sources listed above. The results show that, for the geometry of the nursing infant model at the breast, the highest dose to the infant per photon comes from radionuclides deposited in the mother's liver. For the nursing infant model at the shoulder, the highest dose to the infant per photon comes from radionuclides deposited in the mother's thyroid, and for the nursing infant model in the lap, the highest dose to the infant per photon comes from radionuclides deposited uniformly in the whole body. The dose per photon results were then used to estimate the dose an infant might receive over the lactation period (6 months) due to the incorporation of 1 Bq of a radionuclide by the mother. This information may be used to provide external dose estimates to the infant in the case of a known or suspected radionuclide incorporation by the mother due to, for example, a nuclear medicine procedure.
Assuntos
Aleitamento Materno , Transferência Linear de Energia/fisiologia , Exposição Materna , Radioisótopos/análise , Radioisótopos/farmacocinética , Medição de Risco/métodos , Contagem Corporal Total/métodos , Adulto , Carga Corporal (Radioterapia) , Feminino , Humanos , Lactente , Recém-Nascido , Método de Monte Carlo , Especificidade de Órgãos , Doses de Radiação , Monitoramento de Radiação/métodos , Eficiência Biológica Relativa , Fatores de RiscoRESUMO
The Monte Carlo program 'Visual Monte Carlo-dose calculation' (VMC-dc) uses a voxel phantom to simulate the body organs and tissues, transports photons through this phantom and reports the absorbed dose received by each organ and tissue relevant to the calculation of effective dose as defined in ICRP Publication 60. This paper shows the validation of VMC-dc by comparison with EGSnrc and with a physical phantom containing TLDs. The validation of VMC-dc by comparison with EGSnrc was made for a collimated beam of 0.662 MeV photons irradiating a cube of water. For the validation by comparison with the physical phantom, the case considered was a whole body irradiation with a point 137Cs source placed at a distance of 1 m from the thorax of an Alderson-RANDO phantom. The validation results show good agreement for the doses obtained using VMC-dc and EGSnrc calculations, and from VMC-dc and TLD measurements. The program VMC-dc was then applied to the calculation of doses due to immersion in water containing gamma emitters. The dose conversion coefficients for water immersion are compared with their equivalents in the literature.
Assuntos
Método de Monte Carlo , Imagens de Fantasmas , Radioisótopos/administração & dosagem , Irradiação Corporal Total/normas , Humanos , Masculino , Modelos Anatômicos , Fótons , Dosagem Radioterapêutica/normas , Equivalência TerapêuticaRESUMO
A Monte Carlo program, Visual Monte Carlo (VMC) in vivo, was written to simulate photon transport through an anthropomorphic phantom and to detect radiation emitted from the phantom. VMC in vivo uses a voxel phantom provided by Yale University and may be used to calibrate in vivo systems. This paper shows the application of VMC in vivo to the measurement of 241Am deposited simultaneously in the thoracic region, the bones, the liver and in the rest of the body. The percentages of 241Am in the four body regions were calculated using the biokinetic models established by the ICRP, for a single intake via inhalation. The four regions of the voxel phantom were then 'contaminated' in accordance with the calculated percentages. The calibration factor of the in vivo system was then obtained. This procedure was repeated for the radionuclide distributions obtained 5, 30, 120, 240 and 360 days after intake. VMC in vivo was also used to calculate the calibration factor of the in vivo system in which the radionuclide was assumed to be deposited only in the lung, as is normally done. The activities calculated with the radionuclide distributed in the four body regions as a factor of time, and the activities calculated with the radionuclide deposited in the lung only are compared.
Assuntos
Amerício/farmacocinética , Articulação do Joelho/metabolismo , Fígado/metabolismo , Pulmão/metabolismo , Modelos Biológicos , Modelos Estatísticos , Contagem Corporal Total/métodos , Amerício/análise , Simulação por Computador , Humanos , Exposição por Inalação/análise , Taxa de Depuração Metabólica , Método de Monte Carlo , Especificidade de Órgãos , Imagens de Fantasmas , Fótons , Doses de Radiação , Contagem Corporal Total/normasRESUMO
On 13 September 1987, a radiation accident occurred in the city of Goiânia in Central Brazil. Approximately 250 people were exposed to a 137Cs source from an abandoned radiotherapy unit. At least 14 patients showed some degree of bone marrow depression, and eight developed the classical signs and symptoms of acute radiation syndrome (ARS). Twenty-eight people presented local radiation injuries ranging from first to third degree, and 104 individuals showed evidence of internal contamination. This paper describes the circumstances of the event, the first-aid measures taken, the criteria adopted for triage of the exposed population, and the radiation protection procedures used during the clinical management of the irradiated individuals.