RESUMO
Considering the higher radiosensitivity of children in comparison to adults, studies related to children's exposure to ionising radiation have been long considered of relevance. For this study, the MCNPX2.7.0 Monte Carlo code and four paediatric voxel computational anthropomorphic phantoms, of both genders and aged 5 and 10 years, were used to simulate scenarios, where children are exposed to natural radiation emitted by sources in the ground by radionuclides of40K and of232Th and238U radioactive series. These elements are part of the composition of ten different types of ornamental rocks obtained from three regions of Brazil, and used as architectural material for flooring of houses. The virtual paediatric anthropomorphic phantoms were positioned in a room with dimensions of (4.0 × 5.0 × 2.8) m3filled with atmospheric air and a 3 cm thick granitic floor acting as a uniformly distributed planar gamma radiation source. The walls of the room were composed of 20 cm thick concrete. Gonads, bone marrow, bladder, colon, and skin were found to be the organs which receive the highest doses. The mean values of effective dose per air kerma at 1 m above the ground summed for all three radionuclides, were 0.96 and 0.68 Sv Gy-1for the 5 and 10 year old phantoms, respectively. The obtained results showed that the granitic rocks considered implicate annual effective doses which are 69%-78% lower than the annual limits, recommended by ICRP Publication 103.
Assuntos
Poluentes Radioativos do Ar , Radioatividade , Adulto , Poluentes Radioativos do Ar/análise , Radiação de Fundo , Criança , Pré-Escolar , Feminino , Humanos , Masculino , Método de Monte Carlo , Imagens de Fantasmas , Doses de Radiação , RadiometriaRESUMO
The objective of this study was to estimate the risk of radiation-induced injury to the organs due to ionizing radiation following breast screening recommendations employing digital breast tomosynthesis (DBT) and digital mammography (DM). Using the Monte Carlo method, absorbed doses in the tissues and organs were calculated on an adult female phantom, considering two-view craniocaudal (CC) and mediolateral oblique (MLO) projections for each breast. The results showed differences in the total effective risk due to DM (CC + MLO) and DBT (CC + MLO) examinations in Brazil, ranging from 20.73 cases 10-5(DM) to 27.19 cases 10-5(DBT). Significant differences were also observed in the total effective risk of cancer incidence in the lungs due to DM (CC + MLO) and DBT (CC + MLO), ranging from 1.75×10-01cases 10-5(DM) to 1.76×10-01cases 10-5(DBT). The results indicate that the total effective risk of incidence should be considered as an additional parameter for the evaluation of DBT or DBT + DM program performance.
Assuntos
Neoplasias da Mama , Neoplasias Induzidas por Radiação , Adulto , Mama/diagnóstico por imagem , Neoplasias da Mama/diagnóstico por imagem , Detecção Precoce de Câncer , Feminino , Humanos , Mamografia , Programas de Rastreamento , Neoplasias Induzidas por Radiação/epidemiologia , Neoplasias Induzidas por Radiação/etiologiaRESUMO
Granites are widely used in construction and they may be potential sources of ionizing radiation, due to the presence of radionuclides such as 40Kand decay products from 238Useries and 232Thseries. These radionuclides occur in the minerals constituting the rocks. To evaluate the doses in humans exposed to 40K, and decay products from 238Useries and 232Thseries γ radiation, a room with dimensions of 4.0 × 5.0 × 2.8 m3, with uniformly distributed radiation source on the floor of granitic rocks, was computationally modeled. Adult individuals were represented in the virtual scenario by two virtual anthropomorphic phantoms FASH3 and MASH3, incorporated simultaneously in the software MCNPX 2.7.0. The mean energy deposited on each organ and tissue of FASH3 and MASH3 phantoms was determined using the MCNPX F6 tally (MeV/g/particle), while the photon flux within the room was calculated with the MCNPX F4 tally (MeV/cm2/particle). The organs that obtained the highest conversion coefficients CC[HT](Sv/Gy) were the red bone marrow (0.94), skin (0.90), breast (0.81) and bladder (0.73) for the FASH3; skin (0.89), gonads (0.88), breast (0.79) and bladder (0.70) for the MASH3. The simulated air absorbed dose rates varied between 23.4 (11%) and 25.8 (12%) nGy/h, and the annual dose rates were 0.10 (6%) and 0.11 (6%) mSv/year. These results presented acceptable statistical uncertainties and they are in agreement with the literature. Fluency of photons pointed to the central region of the room floor as the place of greatest exposure. The results showed that the organs closer to the radiation source had the highest deposited energy values. Based on the annual effective dose data obtained, it was possible to note that the values are within the literature. We believe that the methodology used will allow the investigation of any ornamental material that emits natural radiation.
Assuntos
Poluentes Radioativos do Ar/análise , Poluição do Ar em Ambientes Fechados/análise , Modelos Teóricos , Radioisótopos/análise , Dióxido de Silício , Adulto , Brasil , Simulação por Computador , Feminino , Raios gama , Humanos , Masculino , Método de Monte Carlo , Doses de Radiação , RadiometriaRESUMO
ABSTRACT: The influence of the angular deviation of the tube during digital breast tomosynthesis (DBT) acquisition to the dose in the examined breast and in other organs and tissues is not well known. In this work, the Monte Carlo method was used with an adult female virtual anthropomorphic phantom to investigate the impact of this angular variation on the breast dose. The absorbed dose in the examined breast was normalized by the air kerma, which resulted in an absorbed dose coefficient (DT/Kair) for the breast. The absorbed dose in each organ was normalized by the glandular dose in the breast, resulting in the relative organ dose (ROD). An adult female virtual anthropomorphic phantom (FSTA_M50_H50) was incorporated into a scenario containing tomosynthesis equipment with Mo/Mo, Mo/Rh, and W/Rh target/filter combinations and tube voltages of 28 kV. The comparison between the results of the simulations considering digital mammography (DM) and DBT data showed that the DT/Kair values for the examined breast obtained with the DBT parameters were up to 24 times higher than with the DT/Kair obtained with DM parameters. A DT/Kair of 0.97 × 10-1 mGy mGy-1 was obtained in a DBT exam of the right breast. Considering the other organs, the highest ROD values were observed in the thyroid (6.45 × 10-4), eyes (3.87 × 10-4), liver (1.95 × 10-5), and eye lenses (3.21 × 10-3). A variation in the absorbed dose values for the breast and other organs was observed for all projections different from 0°.
Assuntos
Mamografia , Radiometria , Mama/diagnóstico por imagem , Feminino , Humanos , Método de Monte Carlo , Imagens de Fantasmas , Doses de Radiação , Radiometria/métodosRESUMO
PURPOSE: Uterine fibroids affect women mainly of childbearing age, an alternative for the treatment of these fibroids is uterine artery embolization (UAE), a minimally invasive procedure which uses fluoroscopy, providing radiation doses often high, due to the fact that professionals remain in the room throughout the procedure. In this work, equivalent and effective doses were evaluated for the main physician, for the assistant and for the patient during the UAE procedure. METHODS: Doses were calculated using computer simulation with the Monte Carlo Method, and virtual anthropomorphic phantoms, in a typical scenario of interventional radiology with field sizes of 20 × 20, 25 × 25 and 32 × 32 cm2, tube voltages of 70, 80, 90 and 100 kV, and projections of LAO45, RAO45 and PA. RESULTS: The results showed that the highest doses received by the professionals were for the LAO45 projection with 32 × 32 cm2 field size and 100 kV tube voltage, which is in accordance with the existing literature. The highest equivalent doses, without the protective equipment, were in the eyes, skin, breast and stomach for the main physician, and for the assistant they were in the eyes, breast, thyroid and skin. When she used the protective equipment, the highest equivalent doses for the main physician were on the skin, brain, bone marrow and bone surface, and for the assistant they were on the skin, brain, red bone marrow and bone surface. CONCLUSIONS: Effective doses increased up to 3186% for the main physician, and 2462% for the assistant, without protective equipment, thus showing their importance.
Assuntos
Exposição Ocupacional , Embolização da Artéria Uterina , Simulação por Computador , Feminino , Humanos , Método de Monte Carlo , Imagens de Fantasmas , Doses de RadiaçãoRESUMO
Thermoluminescence dosimeters containing boron, such as magnesium tetraborate (MgB4O7), are of interest because of their very high sensitivity, near tissue-equivalent absorption coefficients, low cost, easy handling, and very large linearity range for absorbed dose. Another important parameter that should be considered when working with thermoluminescent dosimeter (TLD) is the mass energy absorption coefficient (µen/ρ), which is a close approximation to the energy available for production of chemical, biological and other effects associated with exposure to ionizing radiation, therefore important in estimating dose in medical and health physics. In this study the mass energy absorption coefficients and energy responses of undoped and some doped magnesium tetraborates were calculated by Monte Carlo N-particle transport code for a range of photon energies between 20â¯keV and 20â¯MeV. The calculated parameters for MgB4O7, MgB4O7:Dy and MgB4O7:Dy,Li were evaluated in comparison with standard TLDs as Al2O3:C and TLD-100 (LiF: Mg, Ti) and ICRU tissue data. The influence of the dopant concentration in the MgB4O7 matrix on the energy dependence of TLD was also investigated. The analyses indicated a good agreement between the simulations and theoretical calculations. The µen/ρ and energy dependence of the materials are higher in the low energy range (Eâ¯<â¯100â¯keV), which is related to the high probability of interaction between radiation and matter due to photoelectric absorption. With regard to the influence of dysprosium concentration in the MgB4O7 matrix an increase in the energy dependence of MgB4O7 for higher concentrations of dopants was observed in the low energy range.
RESUMO
In this study we evaluated the occupational exposures during an abdominal fluoroscopically guided interventional radiology procedure. We investigated the relation between the Body Mass Index (BMI), of the patient, and the conversion coefficient values (CC) for a set of dosimetric quantities, used to assess the exposure risks of medical radiation workers. The study was performed using a set of male and female virtual anthropomorphic phantoms, of different body weights and sizes. In addition to these phantoms, a female and a male phantom, named FASH3 and MASH3 (reference virtual anthropomorphic phantoms), were also used to represent the medical radiation workers. The CC values, obtained as a function of the dose area product, were calculated for 87 exposure scenarios. In each exposure scenario, three phantoms, implemented in the MCNPX 2.7.0 code, were simultaneously used. These phantoms were utilized to represent a patient and medical radiation workers. The results showed that increasing the BMI of the patient, adjusted for each patient protocol, the CC values for medical radiation workers decrease. It is important to note that these results were obtained with fixed exposure parameters.
Assuntos
Abdome/diagnóstico por imagem , Fluoroscopia/efeitos adversos , Pessoal de Saúde , Exposição Ocupacional , Doses de Radiação , Índice de Massa Corporal , Peso Corporal , Simulação por Computador , Feminino , Fluoroscopia/instrumentação , Humanos , Masculino , Modelos Anatômicos , Método de Monte Carlo , Imagens de Fantasmas , Interface Usuário-ComputadorRESUMO
In this work we investigated the way in which conversion coefficients from air kerma-area product for effective doses (CCE) and entrance skin doses (CCESD) in interventional radiology (IR) are affected by variations in the filtration, projection angle of the X-ray beam, lead curtain attached to the surgical table, and suspended shield lead glass in regular conditions of medical practice. Computer simulations were used to model an exposure scenario similar to a real IR room. The patient and the physician were represented by MASH virtual anthropomorphic phantoms, inserted in the MCNPX 2.7.0 radiation transport code. In all cases, the addition of copper filtration also increased the CCE and CCESD values. The highest CCE values were obtained for lateral, cranial and caudal projections. In these projections, the X-ray tube was located above the table, and more scattered radiation reached the middle and upper portions of the physician trunk, where most of the radiosensitive organs are located. Another important result of this study was to show that the physician's protection is 358% higher when the lead curtain and suspended shield lead glasses are used. The values of CCE and CCESD, presented in this study, are an important resource for calculation of effective doses and entrance skin doses in clinical practice.