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https://www.readbyqxmd.com/read/28432792/monte-carlo-study-of-the-chamber-phantom-air-gap-effect-in-a-magnetic-field
#1
Daniel J O'Brien, Gabriel O Sawakuchi
PURPOSE: The aim of this study was to examine the effect of sub-millimeter air gaps that may exist between an ionization chamber and solid phantoms when measurements are performed in a magnetic field. METHODS: Geant4 Monte Carlo simulations were performed using a model of a PTW 30013 Farmer chamber in a water phantom. Symmetrical and asymmetrical air gaps of various thicknesses were modeled surrounding the chamber, and the dose to the air cavity of the chamber was scored in each case...
April 22, 2017: Medical Physics
https://www.readbyqxmd.com/read/28428474/evaluation-of-absorbed-dose-for-cbct-in-image-guided-radiation-therapy-comparison-of-each-devices-and-facilities
#2
Yumiko Kitazato, Noriyuki Kuga, Katsutoshi Shirieda, Masahiro Enzaki, Yuji Nakaguchi, Yoshinobu Shimohigashi, Toshihisa Kawasaki, Masahiko Toyoda, Daisuke Kawahara, Fujio Araki, Shinji Kawamura
Recently, intensity-modulated radiation therapy (IMRT) is used worldwide, highly accurate verification of the location using image-guided radiation therapy (IGRT) has become critical. However, the use of cone-beam computed tomography (CBCT) to ascertain the location each time raises concerns about its influence on radiotherapy dosage and increased radiation exposure. The purpose of this study was to measure the absorbed dose using nine kilovoltage (kV) devices and two megavoltage (MV) devices (total 11 devices) at eight facilities, compare the absorbed dose among the devices, and assess the characteristics of the respective devices to ensure optimal clinical operation...
2017: Nihon Hoshasen Gijutsu Gakkai Zasshi
https://www.readbyqxmd.com/read/28407496/study-of-the-wall-effect-of-the-sample-position-well-of-the-frisch-grid-ionization-chamber
#3
Huaiyong Bai, Zhimin Wang, Luyu Zhang, Haoyu Jiang, Yi Lu, Jinxiang Chen, Guohui Zhang
When measuring the charged particles using a Frisch-grid ionization chamber, the sample is usually placed at the bottom of a sample position well on the common cathode. Thus, there will be the wall effect of the sample position well and this will change the measured energy spectrum of the charged particles. The wall effect of the sample position well is proved to be noticeable by the present work using experiments and simulations.
April 7, 2017: Applied Radiation and Isotopes
https://www.readbyqxmd.com/read/28407129/a-noninferiority-trial-comparing-a-heparin-grafted-membrane-plus-citrate-containing-dialysate-versus-regional-citrate-anticoagulation-results-of-the-cited-study
#4
Björn Meijers, Christoph Metalidis, Thomas Vanhove, Ruben Poesen, Dirk Kuypers, Pieter Evenepoel
Background.: Anticoagulation is a prerequisite for successful haemodialysis. Heparin and low-molecular weight heparins are routinely used despite increased bleeding risk. Regional citrate anticoagulation (RCA) is efficacious, but is laborious and may induce metabolic disturbances. Heparin-grafted membranes are less efficacious. It is not known whether combining citrate-containing dialysate and a heparin-grafted membrane is a valid anticoagulation strategy. Methods.: We performed a randomized crossover noninferiority trial, with a prespecified noninferiority threshold of 10% in maintenance dialysis patients ( n  = 25)...
April 1, 2017: Nephrology, Dialysis, Transplantation
https://www.readbyqxmd.com/read/28405107/response-of-nanodot-optically-stimulated-luminescence-dosimeters-to-therapeutic-electron-beams
#5
Y Retna Ponmalar, Ravikumar Manickam, S Sathiyan, K M Ganesh, R Arun, Henry Finlay Godson
Response of Al2O3:C-based nanoDot optically stimulated luminescence (OSL) dosimeter was studied for the dosimetry of 6, 9, 12, 16, and 20 MeV therapeutic electron beams. With reference to ionization chamber, no change in the response was observed with the change in the energy of electron beams for the field size from 6 cm × 6 cm to 25 cm × 25 cm, dose rates from 100 MU/min to 600 MU/min, and the linearity in the response up to 300 cGy. The fading of the transient signal was higher for 20 MeV electron beam than that of 6 MeV electron beam by about 5% as compared to value at 20 min after irradiation...
January 2017: Journal of Medical Physics
https://www.readbyqxmd.com/read/28405102/measurement-of-total-scatter-factor-for-stereotactic-cones-with-plastic-scintillation-detector
#6
Suresh H Chaudhari, Rishabh Dobhal, Rajesh A Kinhikar, Sudarshan S Kadam, Deepak D Deshpande
Advanced radiotherapy modalities such as stereotactic radiosurgery (SRS) and image-guided radiotherapy may employ very small beam apertures for accurate localized high dose to target. Accurate measurement of small radiation fields is a well-known challenge for many dosimeters. The purpose of this study was to measure total scatter factors for stereotactic cones with plastic scintillation detector and its comparison against diode detector and theoretical estimates. Measurements were performed on Novalis Tx(™) linear accelerator for 6MV SRS beam with stereotactic cones of diameter 6 mm, 7...
January 2017: Journal of Medical Physics
https://www.readbyqxmd.com/read/28383157/development-of-a-novel-low-radiation-absorbent-lok-bar-to-reduce-x-ray-scattering-and-absorption-in-rapidarc-%C3%A2-treatment-planning-and-dose-delivery
#7
Hajime Monzen, Kazuki Kubo, Mikoto Tamura, Masaru Hayakawa, Yasumasa Nishimura
We developed a novel low-radiation-absorbent lok-bar (HM-bar) that is used to secure the immobilizers to the couch. The aim of this study was to investigate the X-ray scattering and absorption properties of the HM-bar in computed tomography (CT) simulation and radiotherapy dose delivery using the Varian Exact™ lok-bar (VL-bar) as a benchmark. CT images were obtained with or without lok-bar, and then each image was visually evaluated for artifacts. The attenuation rates for each lok-bar were measured using a farmer-type ionization chamber (PTW30013) and the I'mRT phantom (IBA Dosimetry GmbH)...
April 6, 2017: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28376951/measurement-error-in-atomic-scale-scanning-transmission-electron-microscopy-energy-dispersive-x-ray-spectroscopy-stem-eds-mapping-of-a-model-oxide-interface
#8
Steven R Spurgeon, Yingge Du, Scott A Chambers
With the development of affordable aberration correctors, analytical scanning transmission electron microscopy (STEM) studies of complex interfaces can now be conducted at high spatial resolution at laboratories worldwide. Energy-dispersive X-ray spectroscopy (EDS) in particular has grown in popularity, as it enables elemental mapping over a wide range of ionization energies. However, the interpretation of atomically resolved data is greatly complicated by beam-sample interactions that are often overlooked by novice users...
April 5, 2017: Microscopy and Microanalysis
https://www.readbyqxmd.com/read/28372412/experimental-setup-for-the-laboratory-investigation-of-micrometeoroid-ablation-using-a-dust-accelerator
#9
Evan Thomas, Jonas Simolka, Michael DeLuca, Mihály Horányi, Diego Janches, Robert A Marshall, Tobin Munsat, John M C Plane, Zoltan Sternovsky
A facility has been developed to simulate the ablation of micrometeoroids in laboratory conditions. An electrostatic dust accelerator is used to generate iron particles with velocities of 10-70 km/s. The particles are then introduced into a chamber pressurized with a target gas, where the pressure is adjustable between 0.01 and 0.5 Torr, and the particle partially or completely ablates over a short distance. An array of biased electrodes above and below the ablation path is used to collect the generated ions/electrons with a spatial resolution of 2...
March 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28369978/monte-carlo-based-investigations-on-the-impact-of-removing-the-flattening-filter-on-beam-quality-specifiers-for-photon-beam-dosimetry
#10
Damian Czarnecki, Björn Poppe, Klemens Zink
PURPOSE: The impact of removing the flattening filter in clinical electron accelerators on the relationship between dosimetric quantities such as beam quality specifiers and the mean photon and electron energies of the photon radiation field was investigated by Monte Carlo simulations. The purpose of this work was to determine the uncertainties when using the well-known beam quality specifiers or energy-based beam specifiers as predictors of dosimetric photon field properties when removing the flattening filter...
April 1, 2017: Medical Physics
https://www.readbyqxmd.com/read/28362367/sublimation-of-dan-matrix-for-the-detection-and-visualization-of-gangliosides-in-rat-brain-tissue-for-maldi-imaging-mass-spectrometry
#11
Sarah Caughlin, Dae Hee Park, Ken K-C Yeung, David F Cechetto, Shawn N Whitehead
Sample preparation is key for optimal detection and visualization of analytes in Matrix-assisted Laser Desorption/Ionization (MALDI) Imaging Mass Spectrometry (IMS) experiments. Determining the appropriate protocol to follow throughout the sample preparation process can be difficult as each step must be optimized to comply with the unique characteristics of the analytes of interest. This process involves not only finding a compatible matrix that can desorb and ionize the molecules of interest efficiently, but also selecting the appropriate matrix deposition technique...
March 23, 2017: Journal of Visualized Experiments: JoVE
https://www.readbyqxmd.com/read/28347899/measurement-of-the-gamma-ray-energy-spectrum-of-the-educational-kinki-university-reactor-utr-kinki
#12
Satoru Endo, Tatsuro Taniguchi, Tsuyoshi Kajimoto, Kenichi Tanaka, Masashi Takada, So Kamada, Tetsuo Horiguchi, Kazuo Fujikawa
The gamma-ray energy spectrum of the Kinki University Reactor (UTR-KINKI) was estimated from Ge detector measurements combined with Monte Carlo N-particle transport criticality calculations. The gamma rays mainly originated from prompt fission components, although small amounts of gamma rays from (n,γ) reactions, fission product gamma rays, and activation gamma rays were detected. The averaged gamma-ray tissue kerma rate in the irradiation port during UTR-KINKI operation at 1W was calculated as 10.5cGy/h based on the estimated gamma-ray energy spectrum...
March 16, 2017: Applied Radiation and Isotopes
https://www.readbyqxmd.com/read/28342596/the-practical-application-of-scintillation-dosimetry-in-small-field-photon-beam-radiotherapy
#13
Elisa Burke, Daniela Poppinga, Andreas A Schönfeld, Dietrich Harder, Björn Poppe, Hui Khee Looe
Plastic scintillation detectors are a new instrument of stereotactic photon-beam dosimetry. The clinical application of the plastic scintillation detector Exradin W1 at the Siemens Artiste and Elekta Synergy accelerators is a matter of current interest. In order to reduce the measurement uncertainty, precautions have to be taken with regard to the geometrical arrangement of the scintillator, the light-guide fiber and the photodiode in the radiation field. To determine the "Cerenkov light ratio" CLR with a type A uncertainty below 1%, the Cerenkov calibration procedure for small-field measurements based on the two-channel spectral method was used...
March 22, 2017: Zeitschrift Für Medizinische Physik
https://www.readbyqxmd.com/read/28332995/three-dimensional-dosimetric-validation-of-a-magnetic-resonance-guided-intensity-modulated-radiation-therapy-system
#14
Leith J Rankine, Stewart Mein, Bin Cai, Austen Curcuru, Titania Juang, Devin Miles, Sasa Mutic, Yuhe Wang, Mark Oldham, H Harold Li
PURPOSE: To validate the dosimetric accuracy of a commercially available magnetic resonance guided intensity modulated radiation therapy (MRgIMRT) system using a hybrid approach: 3-dimensional (3D) measurements and Monte Carlo calculations. METHODS AND MATERIALS: We used PRESAGE radiochromic plastic dosimeters with remote optical computed tomography readout to perform 3D high-resolution measurements, following a novel remote dosimetry protocol. We followed the intensity modulated radiation therapy commissioning recommendations of American Association of Physicists in Medicine Task Group 119, adapted to incorporate 3D data...
April 1, 2017: International Journal of Radiation Oncology, Biology, Physics
https://www.readbyqxmd.com/read/28331147/basic-study-on-visibility-and-water-equivalency-of-a-new-colorless-transparent-bolus-for-electron-radiotherapy
#15
Daiki Maruyama, Shinichi Yamazaki, Emi Honda, Eiji Suzuki, Kouji Hommatsu, Ryo Oshiba, Noboru Sato
Boluses used in electron radiotherapy need to have radiation field visibility and water equivalence. In this report, we have examined field visibility and water equivalence of a new colorless transparent bolus. We examined field visibility, water equivalence, and dose profile. Field visibility was evaluated by comparison to conventional bolus. Water equivalence was investigated by a measured fluence scaling factor. The dose profile was measured by using radiochromic film with the bolus and an ionization chamber in water...
2017: Nihon Hoshasen Gijutsu Gakkai Zasshi
https://www.readbyqxmd.com/read/28326764/utility-of-higher-harmonics-in-electrospray-ionization-fourier-transform-electrostatic-linear-ion-trap-mass-spectrometry
#16
Eric T Dziekonski, Joshua T Johnson, Scott A McLuckey
Mass resolution (M/ΔM fwhm) is observed to linearly increase with harmonic order in a Fourier transform electrostatic linear ion trap (ELIT) mass spectrometer. This behavior was predicted by Grosshans and Marshall for frequency-multiple detection in a Fourier transform ion cyclotron resonance mass spectrometer only for situations when the prominent mechanism for signal decay is ion ejection from the trap. As the analyzer pressure in our ELIT chamber is relatively high, such that collisional scattering and collision-induced dissociation are expected to underlie much of the ion loss, we sought to explore the relationship between harmonic order and mass resolution...
March 30, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/28319041/practical-use-of-a-plastic-scintillator-for-quality-assurance-of-electron-beam-therapy
#17
Katsunori Yogo, Yuya Tatsuno, Masato Tsuneda, Yuki Aono, Daiki Mochizuki, Yoshiki Fujisawa, Akihiro Matsushita, Minoru Ishigami, Hiromichi Ishiyama, Kazushige Hayakawa
Quality assurance (QA) of the clinical electron beam is essential for performing accurate and safe radiation therapy. However, with advances in radiation therapy, QA tends to be labor-intensive and time consuming. Here, we propose the practical use of a tissue-equivalent plastic scintillator for quick and easy QA of clinical electron beams. This tool enabled us to verify simultaneously the constancy of output, beam quality, depth and lateral dose profiles during monthly QAs at lower doses of irradiation (small MUs)...
March 20, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28319031/evaluation-of-the-water-equivalence-of-plastic-materials-in-low-and-high-energy-clinical-proton-beams
#18
A Lourenço, D Shipley, N Wellock, R Thomas, H Bouchard, A Kacperek, F Fracchiolla, S Lorentini, M Schwarz, N MacDougall, G Royle, H Palmans
The aim of this work was to evaluate the water-equivalence of new trial plastics designed specifically for light-ion beam dosimetry as well as commercially available plastics in clinical proton beams. The water-equivalence of materials was tested by computing a plastic-to-water conversion factor, [Formula: see text]. Trial materials were characterized experimentally in 60 MeV and 226 MeV un-modulated proton beams and the results were compared with Monte Carlo simulations using the FLUKA code. For the high-energy beam, a comparison between the trial plastics and various commercial plastics was also performed using FLUKA and Geant4 Monte Carlo codes...
March 20, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28317122/an-anthropomorphic-abdominal-phantom-for-deformable-image-registration-accuracy-validation-in-adaptive-radiation-therapy
#19
Yuliang Liao, Linjing Wang, Xiangdong Xu, Haibin Chen, Jiawei Chen, Guoqian Zhang, Huaiyu Lei, Ruihao Wang, Shuxu Zhang, Xuejun Gu, Xin Zhen, Linghong Zhou
PURPOSE: To design and construct a three-dimensional (3D) anthropomorphic abdominal phantom for geometric accuracy and dose summation accuracy evaluations of deformable image registration (DIR) algorithms for adaptive radiation therapy (ART). METHOD: Organ molds, including liver, kidney, spleen, stomach, vertebra and two metastasis tumors, were 3D printed using contours from an ovarian cancer patient. The organ molds were molded with deformable gels made of different mixtures of polyvinyl chloride (PVC) and the softener dioctyl terephthalate...
March 20, 2017: Medical Physics
https://www.readbyqxmd.com/read/28300383/dosimetry-analysis-of-panoramic-imaging-devices-in-different-sized-phantoms
#20
Muizz A Wahid, Ella Choi, David S MacDonald, Nancy L Ford
The aim of this study is to measure the radiographic dose in adult, adolescent, and child head-sized PMMA phantoms for three panoramic-imaging devices: the panoramic mode on two CBCT machines (Carestream 9300 and i-CAT NG) and the Planmeca ProMax 2D. A SEDENTEXCT dose index adult phantom and custom-built adolescent and pediatric PMMA dosimetry phantoms were used. Panoramic radiographs were performed using a Planmeca ProMax 2D and the panoramic mode on a Carestream 9300 CBCT and an i-CAT NG using the protocols used clinically...
March 2017: Journal of Applied Clinical Medical Physics
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