RESUMO
PURPOSE: The aim of this study was to compare the organ doses assessed through a digital phantom-based and a patient specific-based dosimetric tool in adult routine thorax computed tomography (CT) examinations with reference to physical dose measurements performed in anthropomorphic phantoms. METHODS: Two Monte Carlo based dose calculation tools were used to assess organ doses in routine adult thorax CT examinations. These were a digital phantom-based dosimetry tool (NCICT, National Cancer Institute, USA) and a patient-specific individualized dosimetry tool (ImpactMC, CT Imaging GmbH, Germany). Digital phantoms and patients were classified in four groups according to their water equivalent diameter (Dw). Normalized to volume computed tomography dose index (CTDIvol), organ dose was assessed for lungs, esophagus, heart, breast, active bone marrow, and skin. Organ doses were compared to measurements performed using thermoluminescent detectors (TLDs) in two physical anthropomorphic phantoms that simulate the average adult individual as a male (Alderson Research Labs, USA) and as a female (ATOM Phantoms, USA). RESULTS: The average percent difference of NCICT to TLD and ImpactMC to TLD dose measurements across all organs in both sexes was 13% and 6%, respectively. The average ± 1 standard deviation in dose values across all organs with NCICT, ImpactMC, and TLDs was ± 0.06 (mGy/mGy), ± 0.19 (mGy/mGy), and ± 0.13 (mGy/mGy), respectively. Organ doses decreased with increasing Dw in both NCICT and ImpactMC. CONCLUSION: Organ doses estimated with ImpactMC were in closer agreement to TLDs compared to NCICT. This may be attributed to the inherent property of ImpactMC methodology to generate phantoms that resemble the realistic anatomy of the examined patient as opposed to NCICT methodology that incorporates an anatomical discrepancy between phantoms and patients.
Assuntos
Método de Monte Carlo , Órgãos em Risco , Imagens de Fantasmas , Doses de Radiação , Radiografia Torácica , Tomografia Computadorizada por Raios X , Humanos , Tomografia Computadorizada por Raios X/métodos , Masculino , Feminino , Adulto , Órgãos em Risco/efeitos da radiação , Radiografia Torácica/métodos , Radiometria/métodos , Tórax/diagnóstico por imagem , Tórax/efeitos da radiação , Processamento de Imagem Assistida por Computador/métodos , Planejamento da Radioterapia Assistida por Computador/métodosRESUMO
PURPOSE: To propose an artificial intelligence (AI)-based method for personalized and real-time dosimetry for chest CBCT acquisitions. METHODS: CT images from 113 patients who underwent radiotherapy treatment were collected for simulating thorax examinations using cone-beam computed tomography (CBCT) with the Monte Carlo technique. These simulations yielded organ dose data, used to train and validate specific AI algorithms. The efficacy of these AI algorithms was evaluated by comparing dose predictions with the actual doses derived from Monte Carlo simulations, which are the ground truth, utilizing Bland-Altman plots for this comparative analysis. RESULTS: The absolute mean discrepancies between the predicted doses and the ground truth are (0.9 ± 1.3)% for bones, (1.2 ± 1.2)% for the esophagus, (0.5 ± 1.3)% for the breast, (2.5 ± 1.4)% for the heart, (2.4 ± 2.1)% for lungs, (0.8 ± 0.6)% for the skin, and (1.7 ± 0.7)% for integral. Meanwhile, the maximum discrepancies between the predicted doses and the ground truth are (14.4 ± 1.3)% for bones, (12.9 ± 1.2)% for the esophagus, (9.4 ± 1.3)% for the breast, (14.6 ± 1.4)% for the heart, (21.2 ± 2.1)% for lungs, (10.0 ± 0.6)% for the skin, and (10.5 ± 0.7)% for integral. CONCLUSIONS: AI models that can make real-time predictions of the organ doses for patients undergoing CBCT thorax examinations as part of radiotherapy pre-treatment positioning were developed. The results of this study clearly show that the doses predicted by analyzed AI models are in close agreement with those calculated using Monte Carlo simulations.
Assuntos
Inteligência Artificial , Tomografia Computadorizada de Feixe Cônico Espiral , Humanos , Dosagem Radioterapêutica , Radiometria/métodos , Tomografia Computadorizada de Feixe Cônico/métodos , Método de Monte Carlo , Imagens de Fantasmas , Doses de RadiaçãoRESUMO
PURPOSE: To develop a machine learning-based methodology for patient-specific radiation dosimetry in thoracic and abdomen CT. METHODS: Three hundred and thirty-one thoracoabdominal radiotherapy-planning CT examinations with the respective organ/patient contours were collected retrospectively for the development and validation of segmentation 3D-UNets. Moreover, 97 diagnostic thoracic and 89 diagnostic abdomen CT examinations were collected retrospectively. For each of the diagnostic CT examinations, personalized MC dosimetry was performed. The data derived from MC simulations along with the respective CT data were used for the training and validation of a dose prediction deep neural network (DNN). An algorithm was developed to utilize the trained models and perform patient-specific organ dose estimates for thoracic and abdomen CT examinations. The doses estimated with the DNN were compared with the respective doses derived from MC simulations. A paired t-test was conducted between the DNN and MC results. Furthermore, the time efficiency of the proposed methodology was assessed. RESULTS: The mean percentage differences (range) between DNN and MC dose estimates for the lungs, liver, spleen, stomach, and kidneys were 7.2 % (0.2-24.1 %), 5.5 % (0.4-23.0 %), 7.9 % (0.6-22.3 %), 6.9 % (0.0-23.0 %) and 6.7 % (0.3-22.6 %) respectively. The differences between DNN and MC dose estimates were not significant (p-value = 0.12). Moreover, the mean processing time of the proposed workflow was 99 % lower than the respective time needed for MC-based dosimetry. CONCLUSIONS: The proposed methodology can be used for rapid and accurate patient-specific dosimetry in chest and abdomen CT.
Assuntos
Radiometria , Tomografia Computadorizada por Raios X , Humanos , Estudos Retrospectivos , Método de Monte Carlo , Imagens de Fantasmas , Radiometria/métodos , Tomografia Computadorizada por Raios X/métodos , Aprendizado de Máquina , Doses de Radiação , Abdome/diagnóstico por imagemRESUMO
BACKGROUND: Patient-specific organ-dose estimation in diagnostic CT examinations can provide useful insights on individualized secondary cancer risks, protocol optimization, and patient management. Current dose estimation techniques mainly rely on time-consuming Monte Carlo methods or/and generalized anthropomorphic phantoms. PURPOSE: We proposed a proof-of-concept rapid workflow based on deep learning networks to estimate organ doses for individuals following thorax Computed Tomography (CT) examinations. METHODS: CT scan data from 95 individuals undergoing thorax CT examinations were used. Monte Carlo simulations were performed and three-dimensional (3D) dose distributions for each patient were obtained. A fully connected sequential deep learning network model was constructed and trained for each organ considered in this study. Water-equivalent diameter (WED), scan length, and tube current were the independent variables. Organ doses for heart, lungs, esophagus, and bones were calculated from the Monte Carlo 3D distribution and used to train the deep learning networks. Organ dose predictions from each network were evaluated using an independent data set of 19 patients. RESULTS: The trained networks provided organ dose predictions within a second. There was very good agreement between the deep learning network predictions and reference organ dose values calculated from Monte Carlo simulations. The average difference was -1.5% for heart, -1.6% for esophagus, -1.0% for lungs, and -0.4% for bones in the 95 patients dataset, and -5.1%, 4.3%, 0.9%, and 1.4% respectively in the 19 patients test dataset. CONCLUSIONS: The proposed workflow demonstrated that patient-specific organ-doses can be estimated in nearly real-time using deep learning networks. The workflow can be readily implemented and requires a small set of representative data for training.
Assuntos
Aprendizado Profundo , Humanos , Tomografia Computadorizada por Raios X/métodos , Imagens de Fantasmas , Método de Monte Carlo , Doses de Radiação , Radiometria/métodosRESUMO
Medical ionizing radiation procedures and especially medical imaging are a non negligible source of exposure to patients. Whereas the biological effects of high absorbed doses are relatively well known, the effects of low absorbed doses are still debated. This work presents the development of a computer platform called Image and Radiation Dose BioBank (IRDBB) to manage research data produced in the context of the MEDIRAD project, a European project focusing on research on low doses in the context of medical procedures. More precisely, the paper describes a semantic database linking dosimetric data (such as absorbed doses to organs) to the images corresponding to X-rays exposure (such as CT images) or scintigraphic images (such as SPECT or PET images) that allow measuring the distribution of a radiopharmaceutical. The main contributions of this work are: 1) the implementation of the semantic database of the IRDBB system and 2) an ontology called OntoMEDIRAD covering the domain of discourse involved in MEDIRAD research data, especially many concepts from the DICOM standard modelled according to a realist approach.
Assuntos
Mineração de Dados/métodos , Diagnóstico por Imagem , Documentação/métodos , Processamento de Linguagem Natural , Radiometria , Semântica , Algoritmos , Sistemas de Gerenciamento de Base de Dados , Bases de Dados Factuais , Humanos , Aprendizado de Máquina , Doses de Radiação , Radiografia , Radiometria/métodos , Terminologia como AssuntoRESUMO
PURPOSE: To provide normalized scatter exposure data and methods for reliable estimation of cumulative effective dose and eye-lens equivalent dose to personnel involved in fluoroscopically guided cardiac catheterization (FGCC) procedures. METHODS: An anthropomorphic phantom was placed supine on the table of a modern digital C-arm angiographic system and 17 different fluoroscopic projections commonly employed during FGCC procedures were represented. Scatter exposure rates at the waist and eye level were measured for varying exposure parameters and position in the operating room. The effect of beam field size, patient size, use of radioprotective garments and small variations in projection angulation and table height on scatter radiation was investigated. RESULTS: Apart from the position and use of radio-protective garments, radiation burden to operators during fluoroscopic guidance was found to remarkably depend beam field size (>45% reduction if a 10 × 10 cm(2) instead of 15 × 15 cm(2) fluoroscopy beam is used) and patient size (>25% increased scatter for obese patients). In contrast, the variation of measured scatter exposure from a given projection was found to be <10% when the source to skin distance was altered by ±10 cm or beam angulation of a specific projection was altered by ±10°. CONCLUSION: Presented scatter exposure data charts and methods allow for prospective and retrospective estimation of effective dose and eye-lens equivalent dose to personnel involved in any FGCC procedure. Projection specific maps of scatter exposure produced may enhance familiarization of involved medical staff to good radiation protection practice and optimization of working habits in the cardiac catheterization lab.
Assuntos
Cateterismo Cardíaco , Fluoroscopia , Exposição Ocupacional/análise , Radiometria/métodos , Pessoal de Saúde , HumanosRESUMO
The current study aimed to: a) utilize Monte Carlo simulation methods for the assessment of radiation doses imparted to all organs at risk to develop secondary radiation induced cancer, for patients undergoing radiotherapy for breast cancer; and b) evaluate the effect of breast size on dose to organs outside the irradiation field. A simulated linear accelerator model was generated. The in-field accuracy of the simulated photon beam properties was verified against percentage depth dose (PDD) and dose profile measurements on an actual water phantom. Off-axis dose calculations were verified with thermoluminescent dosimetry (TLD) measurements on a humanoid physical phantom. An anthropomorphic mathematical phantom was used to simulate breast cancer radiotherapy with medial and lateral fields. The effect of breast size on the calculated organ dose was investigated. Local differences between measured and calculated PDDs and dose profiles did not exceed 2% for the points at depths beyond the depth of maximum dose and the plateau region of the profile, respectively. For the penumbral regions of the dose profiles, the distance to agreement (DTA) did not exceed 2 mm. The mean difference between calculated out-of-field doses and TLD measurements was 11.4% ± 5.9%. The calculated doses to peripheral organs ranged from 2.32 cGy up to 161.41 cGy depending on breast size and thus the field dimensions applied, as well as the proximity of the organs to the primary beam. An increase to the therapeutic field area by 50% to account for the large breast led to a mean organ dose elevation by up to 85.2% for lateral exposure. The contralateral breast dose ranged between 1.4% and 1.6% of the prescribed dose to the tumor. Breast size affects dose deposition substantially.
Assuntos
Neoplasias da Mama/radioterapia , Modelos Biológicos , Órgãos em Risco/efeitos da radiação , Planejamento da Radioterapia Assistida por Computador/métodos , Dosimetria Termoluminescente , Simulação por Computador , Feminino , Humanos , Método de Monte Carlo , Dosagem RadioterapêuticaRESUMO
The purpose of this study was to measure the scattered dose to out-of-field organs from head and neck radiotherapy in pediatric patients and to estimate the risk for second cancer induction to individual organs. Radiotherapy for thalamic tumor, brain tumor, acute leukemia and Hodgkin's disease in the neck region was simulated on 5 and 10-year-old pediatric phantoms with a 6 MV photon beam. The radiation dose to thyroid, breast, lung, stomach, ovaries, bladder, liver, uterus, prostate and colon was measured using thermoluminescent dosimeters. The methodology, provided by the BEIR VII report was used for the second cancer risk estimations. Peripheral dose range for a simulated 5-year-old patient was 0.019%-1.572% of the given tumor dose. The corresponding range at the advanced patient age was reduced to 0.018%-1.468%. The second cancer risk per fraction for male patients varied from 3 to 215 per 1,000,000 patients depending upon the age at the time of exposure, primary cancer site and organ scattered dose. The corresponding risk for females was 1-1186 per 1,000,000 patients. The higher risk values were found for breast, thyroid and lung cancer development. The current data concerning the risk magnitude for developing subsequent neoplasms to various out-of-field organs may be of value for health care professionals in the follow-up studies of childhood cancer survivors.
Assuntos
Neoplasias de Cabeça e Pescoço/radioterapia , Neoplasias Induzidas por Radiação/etiologia , Órgãos em Risco/efeitos da radiação , Doses de Radiação , Tolerância a Radiação/efeitos da radiação , Espalhamento de Radiação , Criança , Pré-Escolar , Feminino , Humanos , Masculino , Imagens de FantasmasRESUMO
BACKGROUND: Symptomatic choledocholithiasis can be treated during pregnancy. Conceptus doses ranged from 0.1 mGy to 3 mGy in previous studies. OBJECTIVE: The objectives of the current study were to investigate whether the conceptus dose may exceed the threshold of 10 mGy in the case of a pregnant patient undergoing ERCP, and to provide data for the accurate assessment of a conceptus dose. DESIGN: Monte Carlo methodology and mathematical anthropomorphic phantoms were used to determine normalized conceptus dose data. Phantoms simulated pregnant patients of different body sizes and gestational stages. Monte Carlo simulations were performed to estimate the efficiency of external shielding. SETTING: University hospital. PATIENTS: Twenty-four consecutive patients. INTERVENTIONS: All patients underwent therapeutic ERCP. Exposure parameters and dose-area product were recorded during the procedures. MAIN OUTCOME MEASUREMENTS: The total dose-area product recorded during ERCP procedures ranged between 62 x 10(3) and 491 x 10(3) mGy . cm(2). RESULTS: Monte Carlo normalized conceptus dose data are presented as a function of kV(p), total filtration, gestational stage, and body mass index. The conceptus dose may exceed 10 mGy when the total dose-area product surpasses 130 mGy . cm(2). LIMITATIONS: Variations of conceptus location and size from the average. CONCLUSIONS: Conceptus dose from ERCP may occasionally exceed 10 mGy, the dose above which the analytical dose calculation is recommended. The use of external shielding is unnecessary because the associated dose reduction is negligible. The normalized dose data may be used for the accurate estimation of conceptus dose from an ERCP procedure performed on a pregnant patient, regardless of body size, gestational stage, operating parameters, and equipment used.
Assuntos
Colangiopancreatografia Retrógrada Endoscópica , Feto/efeitos da radiação , Doses de Radiação , Feminino , Humanos , Gravidez , Fatores de RiscoRESUMO
The objective of this study was to estimate the radiation dose and associated risks resulting from fluoroscopically guided percutaneous transluminal angioplasty with or without stent placement in the abdominal region. Average examination parameters for renal and aortoiliac procedures were derived using data from 80 consecutive procedures performed in our institute. Organ and effective doses were estimated for endovascular procedures with the use of a Monte Carlo (MC) transport code and an adult mathematical phantom. Thermoluminescent dosimeters were used in an anthropomorphic phantom to verify MC calculations. Radiation-induced risks were estimated. Results are presented as doses normalized to dose area product, so that the patient dose from any technique and X-ray unit can be easily calculated for iliac and renal PTA/stenting sessions. The average effective dose varied from 75 to 371 microSv per Gycm(2) depending on the beam quality, procedure scheme and sex of the patient. Differences up to 17% were observed between MC-calculated data and data derived from thermoluminescent dosimetry. The radiation-induced cancer risk may be considerable for younger individuals undergoing transluminal angioplasty with stent placement.
Assuntos
Angioplastia , Fluoroscopia/efeitos adversos , Doses de Radiação , Radiografia Abdominal/efeitos adversos , Radiografia Intervencionista/efeitos adversos , Stents , Humanos , Método de Monte Carlo , Doenças Vasculares Periféricas/diagnóstico por imagem , Doenças Vasculares Periféricas/terapia , Imagens de Fantasmas , Obstrução da Artéria Renal/diagnóstico por imagem , Obstrução da Artéria Renal/terapia , Medição de Risco , Estatísticas não Paramétricas , Dosimetria TermoluminescenteRESUMO
The aim of the current study was to (a) provide normalized dose data for the estimation of the radiation dose from upper gastrointestinal tract contrast (UGIC) studies carried out to infants and (b) estimate the average patient dose and risks associated with radiation from UGIC examinations performed in our institution. Organ and effective doses, normalized to entrance skin dose (ESD) and dose area product (DAP) were estimated for UGIC procedures utilizing the Monte Carlo N-particle (MCNP) transport code and two mathematical phantoms, one corresponding to the size of a newborn and one to the size of a 1-year-old child. The validity of the MCNP results was verified by comparison with dose data obtained in physical anthropomorphic phantoms simulating a newborn and a 1-year-old infant using thermoluminescence dosimetry (TLD). Data were also collected from 25 consecutive UGIC examinations performed to infants. Study participants were (a) 12 infants aged from 0.5 to 5.9 months (group 1) and (b) 13 infants aged from 6 to 15 months (group 2). For each examination, ESD and dose to comforters were measured using TLD. Patient effective doses were estimated using normalized dose data obtained in the simulation study. The risk for fatal cancer induction was estimated using appropriate coefficients. The results consist of tabulated dose data normalized to ESD or DAP for the estimation of patient dose. Conversion coefficients were estimated for various tube potentials and beam filtration values. The mean total fluoroscopy time was 1.26 and 1.62 min for groups 1 and 2, respectively. The average effective dose was 1.6 mSv for group 1 and 1.9 mSv for group 2. The risk of cancer attributable to the radiation exposure associated with a typical UGIC study was found to be up to 3 per 10 000 infants undergoing an UGIC examination. The mean radiation dose absorbed by the hands of comforters was 47 microGy. In conclusion, estimation of radiation doses associated with UGIC studies performed to infants can be made using the normalized dose data provided in the current study. Radiation dose values associated with UGIC examinations carried out to infants are not low and should be minimized as much as possible.
Assuntos
Doses de Radiação , Eficiência Biológica Relativa , Medição de Risco/métodos , Dosimetria Termoluminescente/métodos , Trato Gastrointestinal Superior/diagnóstico por imagem , Carga Corporal (Radioterapia) , Simulação por Computador , Meios de Contraste , Feminino , Humanos , Lactente , Recém-Nascido , Modelos Biológicos , Especificidade de Órgãos , Radiografia , Valores de Referência , Raios XRESUMO
PURPOSE: The aim of this study was to determine occupational dose levels for projections commonly used in fluoroscopically guided percutaneous transhepatic biliary (PTB) drainage and stent placement procedures. METHODS: Exposure data from 71 consecutive PTB examinations were analyzed to determine average examination parameters for biliary drainage and stent placement procedures. An anthropomorphic phantom was exposed at three projections common in PTB interventions according to the actual geometric parameters recorded in the patient study. Scattered air-kerma dose rates were measured for neck, waist, and gonad levels at various sites in the interventional radiology laboratory. To produce technique- and instrumentation-independent data, dose rate values were converted to dose-area product (DAP)-normalized air-kerma values. In addition, sets of thermoluminescent dosimetry crystals were placed in both hands of the interventional radiologist to monitor doses during all PTB procedures. RESULTS: Isodose maps of DAP-normalized air-kerma doses in the interventional laboratory for projections commonly used in PTB procedures are presented. To facilitate effective dose estimation, normalized dosimetric data at the interventional radiologist's position are presented for left and right access drainage procedures, metallic stent placement only, and drainage and metallic stent placement in one-session procedures with and without under-couch shielding. Doses to the hands of interventional radiologists are presented for left and right transhepatic biliary access and metallic stent placement. CONCLUSIONS: Body level-specific normalized air-kerma distributions from commonly used projections in PTB procedures may be useful to accurately quantify dose, maximum workloads, and possible radiogenic risks delivered to medical personnel working in the interventional radiology laboratory. Normalized dose data presented will enable occupational exposure estimation from other institutions.
Assuntos
Colestase/diagnóstico por imagem , Fluoroscopia/efeitos adversos , Exposição Ocupacional , Monitoramento de Radiação/métodos , Radiografia Intervencionista/efeitos adversos , Idoso , Colestase/terapia , Feminino , Pessoal de Saúde , Humanos , Masculino , Pessoa de Meia-Idade , Imagens de Fantasmas , Doses de Radiação , Espalhamento de Radiação , StentsRESUMO
PURPOSE: To estimate radiation dose and associated risks after fluoroscopically guided percutaneous transhepatic biliary (PTB) drainage and stent implantation procedures. MATERIALS AND METHODS: Organ and effective doses, normalized to dose-area product (DAP), were estimated for PTB procedures with use of a Monte Carlo transport code and an adult mathematical phantom. Exposure parameters from 51 consecutive patients were used to determine average examination parameters for biliary drainage and stent implantation procedures. Thermoluminescent dosimeters were used in an anthropomorphic phantom to verify Monte Carlo calculations. Radiation-induced cancer and genetic risks were estimated. RESULTS: The results consist of doses normalized to DAP so patient dose from any technique and x-ray unit can be easily calculated for left and right biliary access and for separate or combined biliary and metallic stent implantation sessions. A good agreement was found between Monte Carlo-calculated data and data derived from thermoluminescent dosimetry. The average effective dose varied from 1.8 to 5.4 mSv depending on procedure approach (left vs right access) and procedure scheme. A maximum effective dose of 13 mSv was estimated for 30 minutes of fluoroscopy. CONCLUSIONS: Doses delivered to patients undergoing PTB procedures are comparable to those that arise from computed tomography protocols. Radiation-induced cancer risk may be considerable for young patients undergoing PTB drainage and stent implantation procedures.
Assuntos
Ductos Biliares/efeitos da radiação , Colestase/terapia , Fluoroscopia/efeitos adversos , Doses de Radiação , Stents , Adulto , Idoso , Idoso de 80 Anos ou mais , Procedimentos Cirúrgicos do Sistema Biliar , Feminino , Fluoroscopia/instrumentação , Humanos , Masculino , Pessoa de Meia-Idade , Método de Monte Carlo , Neoplasias Induzidas por Radiação , Imagens de Fantasmas , Radiografia Intervencionista , Eficiência Biológica Relativa , Fatores de Risco , Dosimetria Termoluminescente , Vísceras/efeitos da radiaçãoRESUMO
The purpose of this study was to determine the gonadal dose, effective dose and relevant radiogenic risks associated with pediatric patients undergoing voiding cystourethrography (VCUG). Exposure parameters were monitored in 118 consecutive children undergoing VCUG. The entrance surface dose (ESD) was determined by thermoluminescent dosimeters (TLDs). For male patients, the gonadal dose was determined by TLDs attached on the anterior scrotum. For female patients, the gonadal dose was estimated by converting ESD to the ovarian dose. ESD-to-ovarian dose conversion factors were determined by thermoluminescence dosimetry and physical anthropomorphic phantoms representing newborn and 1-, 5- and 10-year-old individuals. The effective dose was estimated by using ESD and data obtained from the literature. The mean fluoroscopy time and number of radiographs during VCUG were 0.73 min and 2.3 for female and 0.91 min and 3.0 for male pediatric patients, respectively. The gonadal dose range was 0.34-5.17 mGy in boys and 0.36-2.57 mGy in girls. The corresponding ranges of effective dosage were 0.12-1.67 mSv and 0.15-1.45 mSv. Mean radiation risks for genetic anomalies and carcinogenesis following VCUG during childhood were estimated to be up to 15 per million and 125 per million, respectively. Radiation risks associated with pediatric patients undergoing VCUG should not be disregarded if such a procedure is to be justified adequately.
Assuntos
Fluoroscopia/efeitos adversos , Urografia/efeitos adversos , Adolescente , Criança , Pré-Escolar , Meios de Contraste , Feminino , Gônadas/efeitos da radiação , Humanos , Lactente , Recém-Nascido , Masculino , Imagens de Fantasmas , Doses de Radiação , Radiografia Intervencionista , Fatores de Risco , Dosimetria TermoluminescenteRESUMO
Our aim in the present study was to investigate the effects of initial electron beam characteristics on Monte Carlo calculated absorbed dose distribution for a linac 6 MV photon beam. Moreover, the range of values of these parameters was derived, so that the resulted differences between measured and calculated doses were less than 1%. Mean energy, radial intensity distribution and energy spread of the initial electron beam, were studied. The method is based on absorbed dose comparisons of measured and calculated depth-dose and dose-profile curves. All comparisons were performed at 10.0 cm depth, in the umbral region for dose-profile and for depths past maximum for depth-dose curves. Depth-dose and dose-profile curves were considerably affected by the mean energy of electron beam, with dose profiles to be more sensitive on that parameter. The depth-dose curves were unaffected by the radial intensity of electron beam. In contrast, dose-profile curves were affected by the radial intensity of initial electron beam for a large field size. No influence was observed in dose-profile or depth-dose curves with respect to energy spread variations of electron beam. Conclusively, simulating the radiation source of a photon beam, two of the examined parameters (mean energy and radial intensity) of the electron beam should be tuned accurately, so that the resulting absorbed doses are within acceptable precision. The suggested method of evaluating these crucial but often poorly specified parameters may be of value in the Monte Carlo simulation of linear accelerator photon beams.