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https://www.readbyqxmd.com/read/28350702/dose-conversion-coefficients-based-on-taiwanese-reference-phantoms-and-monte-carlo-simulations-for-use-in-external-radiation-protection
#1
Shu-Jun Chang, Jui-Ting Hsu, Shih-Yen Hung, Yan-Lin Liu, Shiang-Huei Jiang, Jay Wu
Reference phantoms are widely applied to evaluate the radiation dose for external exposure. However, the frequently used reference phantoms are based on Caucasians. Dose estimation for Asians using a Caucasian phantom can result in significant errors. This study recruited 40 volunteers whose body sizes are close to the average Taiwanese population. Magnetic resonance imaging was performed to obtain the organ volume for construction of the Taiwanese reference man (TRM) and Taiwanese reference woman (TRW). The dose conversion coefficients (DCC) resulting from photo beams in anterior-posterior, posterior-anterior, right-lateral, left-lateral, and isotropic irradiation geometries were estimated...
May 2017: Health Physics
https://www.readbyqxmd.com/read/28350696/monte-carlo-simulations-comparing-the-response-of-a-novel-hemispherical-tepc-to-existing-spherical-and-cylindrical-tepcs-for-neutron-monitoring-and-dosimetry
#2
David P Broughton, Anthony J Waker
Neutron dosimetry in reactor fields is currently mainly conducted with unwieldy flux monitors. Tissue Equivalent Proportional Counters (TEPCs) have been shown to have the potential to improve the accuracy of neutron dosimetry in these fields, and Multi-Element Tissue Equivalent Proportional Counters (METEPCs) could reduce the size of instrumentation required to do so. Complexity of current METEPC designs has inhibited their use beyond research. This work proposes a novel hemispherical counter with a wireless anode ball in place of the traditional anode wire as a possible solution for simplifying manufacturing...
May 2017: Health Physics
https://www.readbyqxmd.com/read/28350546/comparing-stochastic-proton-interactions-simulated-using-topas-nbio-to-experimental-data-from-fluorescent-nuclear-track-detectors
#3
T S A Underwood, W Sung, C H McFadden, S J McMahon, D C Hall, A L McNamara, H Paganetti, G O Sawakuchi, J Schuemann
Whilst Monte Carlo (MC) simulations of proton energy deposition have been well-validated at the macroscopic level, their microscopic validation remains lacking. Equally, no gold-standard yet exists for experimental metrology of individual proton tracks. In this work we compare the distributions of stochastic proton interactions simulated using the TOPAS-nBio MC platform against confocal microscope data for Al2O3:C,Mg fluorescent nuclear track detectors (FNTDs). We irradiated [Formula: see text] mm(3) FNTD chips inside a water phantom, positioned at seven positions along a pristine proton Bragg peak with a range in water of 12 cm...
April 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28345728/embedding-1d-or-2d-cobalt-carboxylate-substrates-in-3d-coordination-polymers-exhibiting-slow-magnetic-relaxation-behaviors-crystal-structures-high-field-epr-and-magnetic-studies
#4
Nannan Mao, Biquan Zhang, Fan Yu, Xi Chen, Gui-Lin Zhuang, Zhenxing Wang, Zhongwen Ouyang, Tianle Zhang, Bao Li
By utilizing well-designed bifunctional ligands derived from 1H-imidazole-4,5-dicarboxylic acid, magnetic coordination polymers (CPs) that exhibit slow magnetic relaxation at the low temperature regions were constructed and further structurally characterized. In 1, 1D cobalt-carboxyl chains were stabilized in the final structure. In contrast, by adjusting the length of the substituted arms on imidazole-4,5-dicarboxylic acid, a novel 3D CP, 2 containing 2D 6(3) cobalt-carboxyl layer was obtained. A combination of Quantum Monte Carlo (QMC) simulations and the first-principles Density functional theory (DFT) calculations showed that compound 2 features weak ferro- and antiferro-magnetic coupling mechanisms with two different super-exchange paths of -/+/- for syn-anti carboxylate bridges and -/-/- for syn-syn carboxylate bridges...
March 27, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28345047/molecular-beam-brightening-by-shock-wave-suppression
#5
Yair Segev, Natan Bibelnik, Nitzan Akerman, Yuval Shagam, Alon Luski, Michael Karpov, Julia Narevicius, Edvardas Narevicius
Supersonic beams are a prevalent source of cold molecules used in the study of chemical reactions, atom interferometry, gas-surface interactions, precision spectroscopy, molecular cooling, and more. The triumph of this method emanates from the high densities produced in relation to other methods; however, beam density remains fundamentally limited by interference with shock waves reflected from collimating surfaces. We show experimentally that this shock interaction can be reduced or even eliminated by cryocooling the interacting surface...
March 2017: Science Advances
https://www.readbyqxmd.com/read/28344608/a-brief-look-at-model-based-dose-calculation-principles-practicalities-and-promise
#6
REVIEW
Ron S Sloboda, Hali Morrison, Brie Cawston-Grant, Geetha V Menon
Model-based dose calculation algorithms (MBDCAs) have recently emerged as potential successors to the highly practical, but sometimes inaccurate TG-43 formalism for brachytherapy treatment planning. So named for their capacity to more accurately calculate dose deposition in a patient using information from medical images, these approaches to solve the linear Boltzmann radiation transport equation include point kernel superposition, the discrete ordinates method, and Monte Carlo simulation. In this overview, we describe three MBDCAs that are commercially available at the present time, and identify guidance from professional societies and the broader peer-reviewed literature intended to facilitate their safe and appropriate use...
February 2017: Journal of Contemporary Brachytherapy
https://www.readbyqxmd.com/read/28343130/computational-study-of-ibuprofen-removal-from-water-by-adsorption-in-realistic-activated-carbons
#7
Daniel Bahamon, Leticia Carro, Sonia Guri, Lourdes F Vega
Molecular simulations using the Grand Canonical Monte Carlo (GCMC) method have been performed in order to obtain physical insights on how the interaction between ibuprofen (IBP) and activated carbons (ACs) in aqueous mixtures affects IBP removal from water by ACs. A nanoporous carbon model based on units of polyaromatic molecules with different number of rings, defects and polar-oxygenated sites is described. Individual effects of factors such as porous features and chemical heterogeneities in the adsorbents are investigated and quantified...
March 18, 2017: Journal of Colloid and Interface Science
https://www.readbyqxmd.com/read/28341315/initial-clinical-experience-of-postmastectomy-intensity-modulated-proton-therapy-in-patients-with-breast-expanders-with-metallic-ports
#8
Robert W Mutter, Nicholas B Remmes, Mohamed Mh Kahila, Kathy A Hoeft, Deanna H Pafundi, Yan Zhang, Kimberly S Corbin, Sean S Park, Elizabeth S Yan, Valerie Lemaine, Judy C Boughey, Chris J Beltran
PURPOSE: The feasibility of proton postmastectomy radiation therapy in patients reconstructed with expanders has not been previously reported, limiting treatment options. We analyzed the dosimetric impact of the metallic port contained within expanders on intensity modulated proton therapy (IMPT) and report our techniques and quality control for treating patients in this setting. METHODS AND MATERIALS: Twelve patients with the same expander model underwent 2-field IMPT as part of a prospective registry...
December 16, 2016: Practical Radiation Oncology
https://www.readbyqxmd.com/read/28341297/geant4-models-for-the-secondary-radiation-flux-in-the-collimation-system-of-a-300mev-proton-microbeam
#9
Yanxin Dou, David N Jamieson, Jianli Liu, Anlong Li, Liyi Li
In Harbin, we are developing a 300MeV proton microbeam for many applications in space science including upset studies in microelectronic devices, radiation hardness of materials for satellites and radiation effects in human tissues. There are also applications of this facility proposed for proton therapy. The microbeam system will employ a purpose-built proton synchrotron to provide the beam. However there are many challenges to be addressed in the design, construction and operation of this facility. Here we address two important design aspects for which we apply GEANT4 modeling...
December 2016: Physica Medica: PM
https://www.readbyqxmd.com/read/28339846/estimation-of-whole-body-radiation-exposure-from-brachytherapy-for-oral-cancer-using-a-monte-carlo-simulation
#10
Y Ozaki, H Watanabe, A Kaida, M Miura, K Nakagawa, K Toda, R Yoshimura, Y Sumi, T Kurabayashi
Early stage oral cancer can be cured with oral brachytherapy, but whole-body radiation exposure status has not been previously studied. Recently, the International Commission on Radiological Protection Committee (ICRP) recommended the use of ICRP phantoms to estimate radiation exposure from external and internal radiation sources. In this study, we used a Monte Carlo simulation with ICRP phantoms to estimate whole-body exposure from oral brachytherapy. We used a Particle and Heavy Ion Transport code System (PHITS) to model oral brachytherapy with 192Ir hairpins and 198Au grains and to perform a Monte Carlo simulation on the ICRP adult reference computational phantoms...
February 24, 2017: Journal of Radiation Research
https://www.readbyqxmd.com/read/28338980/a-multi-element-thick-gas-electron-multiplier-based-microdosemeter-for-measurement-of-neutrons-dose-equivalent-a-monte-carlo-study
#11
A Moslehi, G Raisali
To determine the dose-equivalent of neutrons in an extended energy range, in the present work a multi-element thick gas electron multiplier-based microdosemeter made of PMMA (Perspex) walls of 10 mm in thickness is designed. Each cavity is filled with the propane-based tissue-equivalent (TE) gas simulating 1 µm of tissue. Also, a few weight fractions of 3He are assumed to be added to the TE gas. The dose-equivalents are determined for 11 neutron energies between thermal and 14 MeV using the lineal energy distributions calculated by Geant4 simulation toolkit and also the lineal energy-based quality factors...
March 14, 2017: Radiation Protection Dosimetry
https://www.readbyqxmd.com/read/28338948/comparing-measured-and-calculated-doses-in-interventional-cardiology-procedures
#12
M W Oliveira da Silva, L V Canevaro, J Hunt, B B D Rodrigues
Interventional cardiology requires complex procedures and can result in high doses and dose rates to the patient and medical staff. The many variables that influence the dose to the patient and staff include the beam position and angle, beam size, kVp, filtration, kerma-area product and focus-skin distance. A number of studies using the Monte Carlo method have been undertaken to obtain prospective dose assessments. In this paper, detailed irradiation scenarios were simulated mathematically and the resulting dose estimates were compared with real measurements made previously under very similar irradiation conditions and geometries...
March 16, 2017: Radiation Protection Dosimetry
https://www.readbyqxmd.com/read/28338151/field-theoretic-simulations-of-random-copolymers-with-structural-rigidity
#13
Shifan Mao, Quinn MacPherson, Jian Qin, Andrew J Spakowitz
Copolymers play an important role in a range of soft-materials applications and biological phenomena. Prevalent works on block copolymer phase behavior use flexible chain models and incorporate interactions using a mean-field approximation. However, when phase separation takes place on length scales comparable to a few monomers, the structural rigidity of the monomers becomes important. In addition, concentration fluctuations become significant at short length scales, rendering the mean-field approximation invalid...
March 24, 2017: Soft Matter
https://www.readbyqxmd.com/read/28337862/bayesian-sensitivity-analysis-of-a-1d-vascular-model-with-gaussian-process-emulators
#14
A Melis, R H Clayton, A Marzo
One-dimensional models of the cardiovascular system can capture the physics of pulse waves, but involve many parameters. Since these may vary among individuals, patient-specific models are difficult to construct. Sensitivity analysis can be used to rank model parameters by their effect on outputs, and to quantify how uncertainty in parameters influences output uncertainty. This type of analysis is often conducted with a Monte Carlo method, where large numbers of model runs are used to assess input-output relations...
March 24, 2017: International Journal for Numerical Methods in Biomedical Engineering
https://www.readbyqxmd.com/read/28337649/conformational-properties-of-block-polyampholytes-adsorbed-on-charged-cylindrical-surfaces
#15
Daniel L Z Caetano, Sidney J de Carvalho
Polyampholytes are polymers that have positive and negative monomers along their chain. The adsorption of polyampholytes on charged surfaces has been the subject of a large number of theoretical, computational and experimental studies due to its importance in a variety of bio and nanothechnological systems. However, computational studies focusing on interaction between polyampholytes and cylindrical charged surfaces are rather scarce. This study, therefore, aims to investigate the conformational properties of block-polyampholytes in the presence of a negatively charged cylinder by means of Metropolis Monte Carlo simulations...
March 2017: European Physical Journal. E, Soft Matter
https://www.readbyqxmd.com/read/28336783/three-dimensional-dosimetry-for-radiation-safety-estimates-from-intrathecal-administration
#16
Jacob Hesterman, Susan Kost, Robert Holt, Howard Dobson, Ajay Verma, P David Mozley
Intrathecal (IT) administration is of growing interest for drug delivery and its utility is being increasingly investigated through imaging. In this work, the three-dimensional (3D) Voxel-Based Internal Dosimetry Application (VIDA) and 4D Extended Cardiac Torso Phantom (XCAT) were extended to provide radiation safety estimates specific to intrathecal administration. Methods: The 3D VIDA dosimetry application Monte Carlo simulation was run using a modified XCAT phantom with additional and edited cerebrospinal fluid (CSF) regions to produce voxel-level absorbed dose per unit cumulated activity maps for nine selected source regions...
March 23, 2017: Journal of Nuclear Medicine: Official Publication, Society of Nuclear Medicine
https://www.readbyqxmd.com/read/28336781/quantitative-evaluation-of-two-scatter-correction-techniques-for-18-f-fdg-brain-pet-mr-imaging-in-regard-to-mr-based-attenuation-correction
#17
Jarmo Teuho, Virva Saunavaara, Tuula Tolvanen, Terhi Tuokkola, Antti Karlsson, Jouni Tuisku, Mika Teräs
In positron emission tomography (PET), corrections for photon scatter and attenuation are essential for visual and quantitative consistency. Magnetic resonance attenuation correction (MRAC) is generally conducted by image segmentation and assignment of discrete attenuation coefficients, which offers limited accuracy compared to computed tomography attenuation correction (CTAC). Potential inaccuracies in MRAC may affect scatter correction, as the attenuation image (µ-map) is used in single scatter simulation (SSS) to calculate the scatter estimate...
March 23, 2017: Journal of Nuclear Medicine: Official Publication, Society of Nuclear Medicine
https://www.readbyqxmd.com/read/28336665/active-sites-for-co2-hydrogenation-to-methanol-on-cu-zno-catalysts
#18
Shyam Kattel, Pedro J Ramírez, Jingguang G Chen, José A Rodriguez, Ping Liu
The active sites over commercial copper/zinc oxide/aluminum oxide (Cu/ZnO/Al2O3) catalysts for carbon dioxide (CO2) hydrogenation to methanol, the Zn-Cu bimetallic sites or ZnO-Cu interfacial sites, have recently been the subject of intense debate. We report a direct comparison between the activity of ZnCu and ZnO/Cu model catalysts for methanol synthesis. By combining x-ray photoemission spectroscopy, density functional theory, and kinetic Monte Carlo simulations, we can identify and characterize the reactivity of each catalyst...
March 24, 2017: Science
https://www.readbyqxmd.com/read/28334300/flight-capacity-of-the-walnut-twig-beetle-coleoptera-scolytidae-on-a-laboratory-flight-mill
#19
Aubree M Kees, Andrea R Hefty, Robert C Venette, Steven J Seybold, Brian H Aukema
The walnut twig beetle, Pityophthorus juglandis Blackman, and associated fungus Geosmithia morbida Kolařík, Freeland, Utley, & Tisserat constitute the insect-fungal complex that causes thousand cankers disease in walnut, Juglans spp., and wingnut, Pterocarya spp. Thousand cankers disease is responsible for the decline of Juglans species throughout the western United States and more recently, the eastern United States and northern Italy. We examined the flight capacity of P. juglandis over 24-h trials on a flight mill in the laboratory...
March 16, 2017: Environmental Entomology
https://www.readbyqxmd.com/read/28333230/bayesian-analysis-of-evolutionary-divergence-with-genomic-data-under-diverse-demographic-models
#20
Yujin Chung, Jody Hey
We present a new Bayesian method for estimating demographic and phylogenetic history using population genomic data. Several key innovations are introduced that allow the study of diverse models within an Isolation with Migration framework. The new method implements a 2-step analysis, with an initial Markov chain Monte Carlo (MCMC) phase that samples simple coalescent trees, followed by the calculation of the joint posterior density for the parameters of a demographic model. In step 1, the MCMC sampling phase, the method uses a reduced state space, consisting of coalescent trees without migration paths, and a simple importance sampling distribution without the demography of interest...
February 25, 2017: Molecular Biology and Evolution
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