Base de dados : MEDLINE
Pesquisa : E07.710 [Categoria DeCS]
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[PMID]:28202324
[Au] Autor:Aldosary G; Safigholi H; Song W; Seuntjens J; Sarfehnia A
[Ad] Endereço:Department of Medical Physics, Cedars Cancer Centre, McGill University Health Centre (Glen Site), DS1 7141, 1001 boul. Decarie, Montreal, Quebec H4A 3J1, Canada. Electronic address: Ghada.Aldosary@McGill.ca.
[Ti] Título:Polarity and ion recombination corrections in continuous and pulsed beams for ionization chambers with high Z chamber walls.
[So] Source:Phys Med;35:102-109, 2017 Mar.
[Is] ISSN:1724-191X
[Cp] País de publicação:Italy
[La] Idioma:eng
[Ab] Resumo:In this work, the response of Farmer-type ionization chambers fitted with high atomic number (Z) walls is studied, and results of the effects of such walls on polarity and ion recombination correction factors in both continuous and pulsed beams are presented. Measurements were made in a continuous Co-60 beam and a pulsed 6MV linac beam using an Exradin-A12 ionization chamber fitted with the manufacturer's C-552 plastic wall, as well as geometrically identical walls made from aluminum, copper and molybdenum. The bias voltage was changed between 10values (range: +50 to +560V). Ion recombination was determined from Jaffé plots and by using the "two-voltage technique". The saturation charge measured with each chamber wall was extrapolated from Jaffé plots. Additionally, the effect of different wall materials on chamber response was studied using MCNP simulations. Results showed that the polarity correction factor is not significantly affected by changes in chamber wall material (within 0.1%). Furthermore, although the saturation charges greatly vary with each chamber wall material, and charge multiplication increases for higher atomic number wall materials, the standard methods of calculating ion recombination yielded results that differed by only 0.2%. Therefore, polarity and ion recombination correction factors are not greatly affected by the chamber wall material. The experimental saturation charges for all the different wall materials agreed well within the uncertainty with MCNP simulations. The breakdown of the linear relationship in Jaffé plots that was previously reported to exist for conventional chamber walls was also observed with the different wall materials.
[Mh] Termos MeSH primário: Equipamentos e Provisões para Radiação
[Mh] Termos MeSH secundário: Alumínio
Radioisótopos de Cobalto
Simulação por Computador
Cobre
Desenho de Equipamento
Transferência Linear de Energia
Molibdênio
Método de Monte Carlo
Plásticos
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Cobalt Radioisotopes); 0 (Plastics); 789U1901C5 (Copper); 81AH48963U (Molybdenum); CPD4NFA903 (Aluminum)
[Em] Mês de entrada:1704
[Cu] Atualização por classe:170410
[Lr] Data última revisão:
170410
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170217
[St] Status:MEDLINE


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[PMID]:28097674
[Au] Autor:Schnerr RS; de Jong AN; Landry G; Jeukens CR; Wierts R
[Ad] Endereço:Department of Radiology, Maastricht UMC+, 6229 HX, Maastricht, The Netherlands.
[Ti] Título:Monte Carlo simulations of ceiling scatter in nuclear medicine: Tc, I and F.
[So] Source:Med Phys;44(3):1113-1119, 2017 Mar.
[Is] ISSN:2473-4209
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:PURPOSE: In the design of nuclear medicine treatment and examination rooms, an important consideration is the shielding required for ionizing radiation from the radioactive isotopes used. The shielding in the walls is normally limited to a height lower than the actual ceiling height. The direct radiation, possibly with build-up correction, can be calculated relatively easily. However, little data are available to estimate the dose contribution from ionizing radiation traveling over the wall shielding and scattering off the ceiling. We aim to determine the contribution of the ceiling scatter to the radiation dose outside nuclear medicine rooms. METHODS: Monte Carlo simulations were performed using Gate for different heights of lead shielding in the wall, and different ceiling heights. A point source in air of Tc (141 keV), I (365 keV) or F (511 keV) was placed 1.0 m above the floor, 3.0 m from the lead shielding. Simulations of ceiling scatter only and for the total radiation dose were performed for these 3 isotopes, 5 different ceiling heights and 4-8 different wall shielding heights, resulting in a total of 165 simulations. This allowed us to compare the contribution of the radiation passing through the shielding and the ceiling scatter. RESULTS: We find that the shielding required for the primary radiation, measured in half-value layers, is an important factor in determining the relative contribution of ceiling scatter. When more than about 4 half-value layers of shielding are used, ceiling scatter becomes the dominant factor and should be taken into account in the shielding design. In many practical cases for low energy photons (e.g. from Tc; 141 keV; half-value layer of 0.26 mm lead), 2 mm of lead is used and ceiling scatter is a dominating factor contributing >~70% of the dose outside the shielded room. For higher energies (e.g. F; 511 keV; half-value layer of 3.9 mm lead) the ceiling scatter is typically less than about 15% when 8 mm of lead shielding is used. CONCLUSIONS: We have performed simulations that allow an estimation of the contribution of ceiling scatter to the radiation dose outside a room, based on the ceiling height, shielding height, and isotope used. This will allow for improved shielding designs in nuclear medicine departments.
[Mh] Termos MeSH primário: Simulação por Computador
Arquitetura de Instituições de Saúde
Método de Monte Carlo
Proteção Radiológica
Radiação Ionizante
Espalhamento de Radiação
[Mh] Termos MeSH secundário: Ar
Arquitetura de Instituições de Saúde/instrumentação
Arquitetura de Instituições de Saúde/métodos
Radioisótopos de Flúor
Radioisótopos do Iodo
Chumbo
Modelos Teóricos
Medicina Nuclear/instrumentação
Medicina Nuclear/métodos
Compostos de Organotecnécio
Fótons
Dose de Radiação
Equipamentos e Provisões para Radiação
Proteção Radiológica/métodos
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Fluorine Radioisotopes); 0 (Iodine Radioisotopes); 0 (Organotechnetium Compounds); 2P299V784P (Lead)
[Em] Mês de entrada:1703
[Cu] Atualização por classe:170328
[Lr] Data última revisão:
170328
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170119
[St] Status:MEDLINE
[do] DOI:10.1002/mp.12113


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[PMID]:28094853
[Au] Autor:Petersson K; Jaccard M; Germond JF; Buchillier T; Bochud F; Bourhis J; Vozenin MC; Bailat C
[Ad] Endereço:CHUV, Institut de Radiophysique, Rue du Grand-Pré 1, CH-1007, Lausanne, Switzerland.
[Ti] Título:High dose-per-pulse electron beam dosimetry - A model to correct for the ion recombination in the Advanced Markus ionization chamber.
[So] Source:Med Phys;44(3):1157-1167, 2017 Mar.
[Is] ISSN:2473-4209
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:PURPOSE: The purpose of this work was to establish an empirical model of the ion recombination in the Advanced Markus ionization chamber for measurements in high dose rate/dose-per-pulse electron beams. In addition, we compared the observed ion recombination to calculations using the standard Boag two-voltage-analysis method, the more general theoretical Boag models, and the semiempirical general equation presented by Burns and McEwen. METHODS: Two independent methods were used to investigate the ion recombination: (a) Varying the grid tension of the linear accelerator (linac) gun (controls the linac output) and measuring the relative effect the grid tension has on the chamber response at different source-to-surface distances (SSD). (b) Performing simultaneous dose measurements and comparing the dose-response, in beams with varying dose rate/dose-per-pulse, with the chamber together with dose rate/dose-per-pulse independent Gafchromic™ EBT3 film. Three individual Advanced Markus chambers were used for the measurements with both methods. All measurements were performed in electron beams with varying mean dose rate, dose rate within pulse, and dose-per-pulse (10  ≤ mean dose rate ≤ 10 Gy/s, 10  ≤ mean dose rate within pulse ≤ 10  Gy/s, 10  ≤ dose-per-pulse ≤ 10  Gy), which was achieved by independently varying the linac gun grid tension, and the SSD. RESULTS: The results demonstrate how the ion collection efficiency of the chamber decreased as the dose-per-pulse increased, and that the ion recombination was dependent on the dose-per-pulse rather than the dose rate, a behavior predicted by Boag theory. The general theoretical Boag models agreed well with the data over the entire investigated dose-per-pulse range, but only for a low polarizing chamber voltage (50 V). However, the two-voltage-analysis method and the Burns & McEwen equation only agreed with the data at low dose-per-pulse values (≤ 10 and ≤ 10  Gy, respectively). An empirical model of the ion recombination in the chamber was found by fitting a logistic function to the data. CONCLUSIONS: The ion collection efficiency of the Advanced Markus ionization chamber decreases for measurements in electron beams with increasingly higher dose-per-pulse. However, this chamber is still functional for dose measurements in beams with dose-per-pulse values up toward and above 10 Gy, if the ion recombination is taken into account. Our results show that existing models give a less-than-accurate description of the observed ion recombination. This motivates the use of the presented empirical model for measurements with the Advanced Markus chamber in high dose-per-pulse electron beams, as it enables accurate absorbed dose measurements (uncertainty estimation: 2.8-4.0%, k = 1). The model depends on the dose-per-pulse in the beam, and it is also influenced by the polarizing chamber voltage, with increasing ion recombination with a lowering of the voltage.
[Mh] Termos MeSH primário: Elétrons
Modelos Teóricos
Equipamentos e Provisões para Radiação
Radiometria/métodos
[Mh] Termos MeSH secundário: Imagens de Fantasmas
Radiometria/instrumentação
Água
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
059QF0KO0R (Water)
[Em] Mês de entrada:1703
[Cu] Atualização por classe:170328
[Lr] Data última revisão:
170328
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170118
[St] Status:MEDLINE
[do] DOI:10.1002/mp.12111


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[PMID]:28094849
[Au] Autor:Stelljes TS; Looe HK; Harder D; Poppe B
[Ad] Endereço:University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University Oldenburg, Germany.
[Ti] Título:The "collimator monitoring fill factor" of a two-dimensional detector array, a measure of its ability to detect collimation errors.
[So] Source:Med Phys;44(3):1128-1138, 2017 Mar.
[Is] ISSN:2473-4209
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:PURPOSE: Two-dimensional detector arrays are routinely used for constancy checks and treatment plan verification in photon-beam radiotherapy. In addition to the spatial resolution of the dose profiles, the "coverage" of the radiation field with respect to the detection of any beam collimation deficiency appears as the second characteristic feature of a detector array. The here proposed "collimator monitoring fill factor" (CM fill factor) has been conceived to serve as a quantitative characteristic of this "coverage". METHODS: The CM fill factor is defined as the probability of a 2D array to detect any collimator position error. Therefore, it is represented by the ratio of the "sensitive area" of a single detector, in which collimator position errors are detectable, and the geometrical "cell area" associated with this detector within the array. Numerical values of the CM fill factor have been Monte Carlo simulated for 2D detector arrays equipped with air-vented ionization chambers, liquid-filled ionization chambers and diode detectors and were compared with the "FWHM fill factor" defined by Gago-Arias et al. (2012). RESULTS: For arrays with vented ionization chambers, the differences between the CM fill factor and the FWHM fill factor are moderate, but occasionally the latter exceeds unity. For narrower detectors such as liquid-filled ionization chambers and Si diodes and for small sampling distances, large differences between the FWHM fill factor and the CM fill factor have been observed. These differences can be explained by the shapes of the fluence response functions of these narrow detectors. CONCLUSIONS: A new parameter "collimator monitoring fill factor" (CM fill factor), applicable to quantitate the collimator position error detection probability of a 2D detector array, has been proposed. It is designed as a help in classifying the clinical performance of two-dimensional detector arrays in photon-beam radiotherapy.
[Mh] Termos MeSH primário: Terapia com Prótons/instrumentação
Equipamentos e Provisões para Radiação
Planejamento da Radioterapia Assistida por Computador/instrumentação
Erros de Configuração em Radioterapia
[Mh] Termos MeSH secundário: Algoritmos
Simulação por Computador
Método de Monte Carlo
Probabilidade
Erros de Configuração em Radioterapia/prevenção & controle
Silício
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
Z4152N8IUI (Silicon)
[Em] Mês de entrada:1703
[Cu] Atualização por classe:170328
[Lr] Data última revisão:
170328
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170118
[St] Status:MEDLINE
[do] DOI:10.1002/mp.12106


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[PMID]:28079260
[Au] Autor:Toftegaard J; Hansen R; Ravkilde T; Macek K; Poulsen PR
[Ad] Endereço:Department of Oncology, Aarhus University Hospital, Aarhus C, 8000, Denmark.
[Ti] Título:An experimentally validated couch and MLC tracking simulator used to investigate hybrid couch-MLC tracking.
[So] Source:Med Phys;44(3):798-809, 2017 Mar.
[Is] ISSN:2473-4209
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:PURPOSE/OBJECTIVE: Couch and MLC tracking are two novel techniques to mitigate intrafractional tumor motion on a conventional linear accelerator, but both techniques still have residual dosimetric errors. Here, we first propose and experimentally validate a software tool to simulate couch and MLC tracking, and then use the simulator to study hybrid couch-MLC tracking for improved tracking performance. MATERIALS AND METHODS: The tracking simulator requires a treatment plan and a motion trajectory as input and simulates the delivered monitor units and motion of all accelerator parts as function of time. The simulator outputs accelerator log files synchronized with the target motion as well as the MLC exposure error, which is a simple dose error surrogate. A series of couch and MLC tracking experiments were used to determine appropriate parameters for the simulator dynamics and to validate the simulator by its ability to reproduce the experimental tracking accuracy. Three hybrid couch-MLC tracking strategies were investigated. All strategies divided the target motion in beam's eye view into motion perpendicular and parallel to the MLC leaves. In the hybrid strategies, couch tracking compensated for the following target motion components (in order of decreasing couch tracking contribution): (a) all perpendicular motion, (b) residual perpendicular motion less than half a leaf width, and (c) persistent residual perpendicular motion that was stable at a time scale of 1s. MLC tracking compensated for the remaining target motion. All tracking strategies were simulated with two prostate and two lung cancer single-arc VMAT plans using 695 prostate trajectories and 160 lung tumor trajectories. The tracking error was quantified as the MLC exposure error. The couch motion was quantified as the mean speed, acceleration, and jerk of the couch. RESULTS: The simulator reproduced the experimental gantry position with a mean (maximum) root-mean-square (rms) error of 0.07°(0.2°). The geometrical rms tracking error was reproduced with mean (maximum) absolute errors of 0.20 mm(0.23 mm) and 0.1 mm(0.23 mm) for MLC tracking parallel and perpendicular to the MLC leaves, and 0.40 mm(0.46 mm), 0.09 mm(0.25 mm), and 0.20 mm(0.46 mm) for couch tracking in the left-right, anterior-posterior, and cranio-caudal directions. The MLC exposure error of VMAT MLC tracking was reproduced with a mean absolute error of 5.6%. All hybrid tracking strategies reduced the couch motion relative to pure couch tracking and improved the tracking accuracy compared with pure MLC tracking. The mean MLC exposure error reduction relative to no tracking was 66.6% (couch tracking), 72.9% (hybrid (1)), 70.2% (2), 59.1% (3), and 55.6% (MLC tracking) for lung tumor motion and 76.5% (couch tracking), 76.1% (1), 74.3% (2), 72.3% (3), and 35.9% (MLC tracking) for prostate motion. For prostate motion, pure MLC tracking resulted in rather large MLC exposure errors that were more than halved with all hybrid tracking strategies. CONCLUSION: A couch and MLC tracking simulator was developed and experimentally validated against a series of tracking experiments. All hybrid couch-MLC tracking strategies improved MLC tracking. Two strategies also improved couch tracking of lung tumors. In particular, MLC tracking of prostate may be greatly improved by a modest degree of couch motion.
[Mh] Termos MeSH primário: Simulação por Computador
Movimento (Física)
Aceleradores de Partículas
Equipamentos e Provisões para Radiação
Planejamento da Radioterapia Assistida por Computador/métodos
Software
[Mh] Termos MeSH secundário: Seres Humanos
Neoplasias Pulmonares/fisiopatologia
Neoplasias Pulmonares/radioterapia
Masculino
Movimento
Neoplasias da Próstata/fisiopatologia
Neoplasias da Próstata/radioterapia
Planejamento da Radioterapia Assistida por Computador/instrumentação
Radioterapia de Intensidade Modulada/instrumentação
Radioterapia de Intensidade Modulada/métodos
[Pt] Tipo de publicação:JOURNAL ARTICLE; VALIDATION STUDIES
[Em] Mês de entrada:1703
[Cu] Atualização por classe:170328
[Lr] Data última revisão:
170328
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:170113
[St] Status:MEDLINE
[do] DOI:10.1002/mp.12104


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[PMID]:27487868
[Au] Autor:Chow PE; Thomas DH; Agazaryan N; Cao M; Low DA; Yang Y; Steinberg ML; Lee P; Lamb JM
[Ad] Endereço:Department of Radiation Oncology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095.
[Ti] Título:Technical Note: Dosimetric effects of couch position variability on treatment plan quality with an MRI-guided Co-60 radiation therapy machine.
[So] Source:Med Phys;43(8):4514, 2016 Aug.
[Is] ISSN:2473-4209
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:PURPOSE: Magnetic resonance imaging (MRI) guidance in radiation therapy brings real-time imaging and adaptive planning into the treatment vault where it can account for interfraction and intrafraction movement of soft tissue. The only commercially available MRI-guided radiation therapy device is a three-head (60)Co and MRI system with an integrated treatment planning system (TPS). Couch attenuation of the beam of up to 20% is well modeled in the TPS. Variations in the patient's day-to-day position introduce discrepancies in the actual couch attenuation as modeled in the treatment plan. For this reason, the authors' institution avoids plans with beams that pass through or near the couch edges. This study investigates the effects of differential beam attenuation by the couch due to couch shifts in order to determine whether couch edge avoidance restrictions can be lifted. Couch shifts were simulated using a Monte Carlo treatment planning system and ion chamber measurements performed for validation. METHODS: A total of 27 plans from 23 patients were investigated. Couch shifts of 1 and 2 cm were introduced in combinations of lateral and vertical directions to simulate patient position variations giving 16 shifted plans per reference plan. The 1 and 2 cm shifts were based on shifts recorded in 320 treatment fractions. RESULTS: Following TG176 recommendations for measurement methods, couch attenuation measurements agreed with TPS modeled attenuation to within 2.1%. Planning target volume D95 changed less than 1% for 1 and 2 cm couch shifts in only the x-direction and less than 3% for all directions. CONCLUSIONS: Dosimetry of all plans tested was robust to couch shifts up to ±2 cm. In general, couch shifts resulted in clinically insignificant dosimetric deviations. It is conceivable that in certain cases with large systematic couch shifts and plans that are particularly sensitive to shifts, dosimetric changes might rise to a clinically significant level.
[Mh] Termos MeSH primário: Radioisótopos de Cobalto/uso terapêutico
Imagem por Ressonância Magnética/instrumentação
Posicionamento do Paciente/instrumentação
Equipamentos e Provisões para Radiação
Planejamento da Radioterapia Assistida por Computador/instrumentação
Radioterapia Guiada por Imagem/instrumentação
[Mh] Termos MeSH secundário: Simulação por Computador
Seres Humanos
Imagem por Ressonância Magnética/métodos
Modelos Teóricos
Método de Monte Carlo
Neoplasias/diagnóstico por imagem
Neoplasias/radioterapia
Posicionamento do Paciente/métodos
Radiometria
Dosagem Radioterapêutica
Planejamento da Radioterapia Assistida por Computador/métodos
Radioterapia Guiada por Imagem/métodos
[Pt] Tipo de publicação:JOURNAL ARTICLE; VALIDATION STUDIES
[Nm] Nome de substância:
0 (Cobalt Radioisotopes)
[Em] Mês de entrada:1703
[Cu] Atualização por classe:170308
[Lr] Data última revisão:
170308
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160805
[St] Status:MEDLINE
[do] DOI:10.1118/1.4955116


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[PMID]:27370122
[Au] Autor:Saenz DL; Kirby N; Gutiérrez AN
[Ad] Endereço:Department of Radiation Oncology, School of Medicine, Cancer Therapy and Research Center, The University of Texas Health Science Center San Antonio, San Antonio, Texas 78229.
[Ti] Título:Characterization of air temperature in modern ion chambers due to phantom geometry and ambient temperature changes.
[So] Source:Med Phys;43(7):4032, 2016 Jul.
[Is] ISSN:2473-4209
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:PURPOSE: Temperature and pressure corrections are necessary to account for the varying mass of air in the sensitive volume of a vented ionization chamber (IC) when performing absolute dose measurements. Locations commonly used to measure the presumed IC air temperature may not accurately represent the chamber cavity air temperature, and phantoms undergoing temperature changes further compound the problem. Prior studies have characterized thermal equilibrium in separate phantoms for Farmer chambers alone. However, the purpose of this study was to characterize the cavity air temperature dependence on changes in the ambient temperature and phantom geometry configuration for a wider and more modern variety of chambers to determine if previously published wait times apply to these chambers as well. METHODS: Thermal conduction properties were experimentally investigated by modifying a PTW 0.3 cm(3) Semiflex IC with a thermocouple replacing the central electrode. Air cavity temperature versus time was recorded in three phantom geometries characteristic of common absolute dose measurements. The phantoms were (15 ± 1) °C before measurement with an IC at the treatment vault temperature of (21 ± 1) °C. Simulations were conducted to provide a theoretical basis for the measurements and to simulate temperature response of a PTW PinPoint® and Farmer chamber. The simulation methods were first validated by comparison with measured Semiflex chamber thermal response curves before extension to the other chambers. RESULTS: Two thermal equilibria curves were recorded on different time scales. IC temperature initially dropped to the colder phantom temperature but subsequently increased as the phantom itself equilibrated with the warmer room temperature. In a large phantom of dimensions (25.5 × 25.5 × 23.4) cm(3), 3 min was required before the IC temperature reached within 0.5 °C of its equilibrium within the phantom. Similarly, wait times of 2 min were needed for 7.5 and 2 cm slab phantoms. CONCLUSIONS: Recording of temperature in the phantom was deemed far more accurate than measurement in ambient air due to the air cavity thermally equilibrating with phantom temperature instead of the vented ambient air. Wait times of 3 and 2 min are needed for a cube and 7.5 cm slab phantom, respectively, to achieve 0.2% dosimetric accuracy (temperature accuracy of 0.5 °C). Chamber volume alone did not determine wait times, as a 0.3 cm(3) IC required a longer wait time than a Farmer chamber, suggesting wall thickness as an important variable as well.
[Mh] Termos MeSH primário: Modelos Teóricos
Imagens de Fantasmas
Equipamentos e Provisões para Radiação
Temperatura Ambiente
[Mh] Termos MeSH secundário: Ar
Simulação por Computador
Desenho de Equipamento
[Pt] Tipo de publicação:JOURNAL ARTICLE; VALIDATION STUDIES
[Em] Mês de entrada:1703
[Cu] Atualização por classe:170308
[Lr] Data última revisão:
170308
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160703
[St] Status:MEDLINE
[do] DOI:10.1118/1.4953195


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[PMID]:27277020
[Au] Autor:Larsson JC; Lundström U; Hertz HM
[Ad] Endereço:Biomedical and X-ray Physics, Department of Applied Physics, KTH Royal Institute of Technology/Albanova, Stockholm 10691, Sweden.
[Ti] Título:Characterization of scintillator-based detectors for few-ten-keV high-spatial-resolution x-ray imaging.
[So] Source:Med Phys;43(6):2731-2740, 2016 Jun.
[Is] ISSN:2473-4209
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:PURPOSE: High-spatial-resolution x-ray imaging in the few-ten-keV range is becoming increasingly important in several applications, such as small-animal imaging and phase-contrast imaging. The detector properties critically influence the quality of such imaging. Here the authors present a quantitative comparison of scintillator-based detectors for this energy range and at high spatial frequencies. METHODS: The authors determine the modulation transfer function, noise power spectrum (NPS), and detective quantum efficiency for Gadox, needle CsI, and structured CsI scintillators of different thicknesses and at different photon energies. An extended analysis of the NPS allows for direct measurements of the scintillator effective absorption efficiency and effective light yield as well as providing an alternative method to assess the underlying factors behind the detector properties. RESULTS: There is a substantial difference in performance between the scintillators depending on the imaging task but in general, the CsI based scintillators perform better than the Gadox scintillators. At low energies (16 keV), a thin needle CsI scintillator has the best performance at all frequencies. At higher energies (28-38 keV), the thicker needle CsI scintillators and the structured CsI scintillator all have very good performance. The needle CsI scintillators have higher absorption efficiencies but the structured CsI scintillator has higher resolution. CONCLUSIONS: The choice of scintillator is greatly dependent on the imaging task. The presented comparison and methodology will assist the imaging scientist in optimizing their high-resolution few-ten-keV imaging system for best performance.
[Mh] Termos MeSH primário: Equipamentos e Provisões para Radiação
Radiografia/instrumentação
[Mh] Termos MeSH secundário: Césio
Desenho de Equipamento
Iodetos
Fótons
Radiografia/métodos
Raios X
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Iodides); 1KSV9V4Y4I (Cesium); U1P3GVC56L (cesium iodide)
[Em] Mês de entrada:1702
[Cu] Atualização por classe:170511
[Lr] Data última revisão:
170511
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160610
[St] Status:MEDLINE
[do] DOI:10.1118/1.4948687


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[PMID]:27167287
[Au] Autor:Wunderle KA; Rakowski JT; Dong FF
[Ad] Endereço:Cleveland Clinic; Wayne State University School of Medicine. kwunderle@gmail.com.
[Ti] Título:Effect of fluoroscopic X-ray beam spectrum on air-kerma measurement accuracy: implications for establishing correction coefficients on interventional fluoroscopes with KAP meters.
[So] Source:J Appl Clin Med Phys;17(3):467-474, 2016 05 08.
[Is] ISSN:1526-9914
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:The first goal of this study was to investigate the accuracy of the displayed reference plane air kerma (Ka,r) or air kerma-area product (Pk,a) over a broad spectrum of X-ray beam qualities on clinically used interventional fluoroscopes incorporating air kerma-area product meters (KAP meters) to measure X-ray output. The second goal was to investigate the accuracy of a correction coefficient (CC) determined at a single beam quality and applied to the measured Ka,r over a broad spectrum of beam qualities. Eleven state-of-the-art interventional fluoroscopes were evaluated, consisting of eight Siemens Artis zee and Artis Q systems and three Philips Allura FD systems. A separate calibrated 60 cc ionization chamber (external chamber) was used to determine the accuracy of the KAP meter over a broad range of clinically used beam qualities. For typical adult beam qualities, applying a single CC deter-mined at 100 kVp with copper (Cu) in the beam resulted in a deviation of < 5% due to beam quality variation. This result indicates that applying a CC determined using The American Association of Physicists in Medicine Task Group 190 protocol or a similar protocol provides very good accuracy as compared to the allowed ± 35% deviation of the KAP meter in this limited beam quality range. For interventional fluoroscopes dedicated to or routinely used to perform pediatric interventions, using a CC established with a low kVp (~ 55-60 kVp) and large amount of Cu filtration (~ 0.6-0.9 mm) may result in greater accuracy as compared to using the 100 kVp values. KAP meter responses indicate that fluoroscope vendors are likely normalizing or otherwise influencing the KAP meter output data. Although this may provide improved accuracy in some instances, there is the potential for large discrete errors to occur, and these errors may be difficult to identify.
[Mh] Termos MeSH primário: Calibragem/normas
Fluoroscopia/normas
Melhoria de Qualidade/normas
Dosímetros de Radiação/normas
Equipamentos e Provisões para Radiação/normas
[Mh] Termos MeSH secundário: Adulto
Seres Humanos
Raios X
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Em] Mês de entrada:1704
[Cu] Atualização por classe:170913
[Lr] Data última revisão:
170913
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160512
[St] Status:MEDLINE
[do] DOI:10.1120/jacmp.v17i3.6092


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[PMID]:27036792
[Au] Autor:Kumar SV; Tare ST; Upalekar YV; Tsering T
[Ad] Endereço:Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India.
[Ti] Título:Dose controlled low energy electron irradiator for biomolecular films.
[So] Source:Rev Sci Instrum;87(3):034302, 2016 Mar.
[Is] ISSN:1089-7623
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:We have developed a multi target, Low Energy Electron (LEE), precise dose controlled irradiator for biomolecular films. Up to seven samples can be irradiated one after another at any preset electron energy and dose under UHV conditions without venting the chamber. In addition, one more sample goes through all the steps except irradiation, which can be used as control for comparison with the irradiated samples. All the samples are protected against stray electron irradiation by biasing them at -20 V during the entire period, except during irradiation. Ethernet based communication electronics hardware, LEE beam control electronics and computer interface were developed in house. The user Graphical User Interface to control the irradiation and dose measurement was developed using National Instruments Lab Windows CVI. The working and reliability of the dose controlled irradiator has been fully tested over the electron energy range of 0.5 to 500 eV by studying LEE induced single strand breaks to ΦX174 RF1 dsDNA.
[Mh] Termos MeSH primário: DNA
Elétrons
Dose de Radiação
Equipamentos e Provisões para Radiação
[Mh] Termos MeSH secundário: DNA/genética
Quebras de DNA/efeitos da radiação
Desenho de Equipamento
Proteção Radiológica
Software
Interface Usuário-Computador
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
9007-49-2 (DNA)
[Em] Mês de entrada:1612
[Cu] Atualização por classe:161231
[Lr] Data última revisão:
161231
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160403
[St] Status:MEDLINE
[do] DOI:10.1063/1.4944812



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