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https://www.readbyqxmd.com/read/28405104/structural-shielding-design-of-a-6-mv-flattening-filter-free-linear-accelerator-indian-scenario
#1
Bibekananda Mishra, T Palani Selvam, P K Dash Sharma
Detailed structural shielding of primary and secondary barriers for a 6 MV medical linear accelerator (LINAC) operated with flattening filter (FF) and flattening filter free (FFF) modes are calculated. The calculations have been carried out by two methods, one using the approach given in National Council on Radiation Protection (NCRP) Report No. 151 and the other based on the monitor units (MUs) delivered in clinical practice. Radiation survey of the installations was also carried out. NCRP approach suggests that the primary and secondary barrier thicknesses are higher by 24% and 26%...
January 2017: Journal of Medical Physics
https://www.readbyqxmd.com/read/28374591/diversity-and-hierarchy-in-supramolecular-assemblies-of-triphenylalanine-from-laminated-helical-ribbons-to-toroids
#2
Enric Mayans, Jordi Casanovas, Ana M Gil, Ana I Jiménez, Carlos Cativiela, Jordi Puiggalí, Carlos Alemán
Microstructures from small phenylalanine-based peptides have attracted great attention lately because these compounds are considered to be a new class of tunable materials. In spite of the extensive studies on uncapped diphenylalanine and tetraphenylalanine peptides, studies on the self-assembly of uncapped triphenylananine (FFF) are very scarce and nonsystematic. In this work, we demonstrate that FFF assemblies can organize in a wide number of well-defined supramolecular structures, which include laminated helical-ribbons, leaflike dendrimers, doughnut-, needle-, and flower-shapes...
April 11, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28336006/influence-of-the-integral-quality-monitor-transmission-detector-on-high-energy-photon-beams-a-multi-centre-study
#3
Bozidar Casar, Marlies Pasler, Sonja Wegener, David Hoffman, Cinzia Talamonti, Jianguo Qian, Ignasi Mendez, Denis Brojan, Bruce Perrin, Martijn Kusters, Richard Canters, Stefania Pallotta, Primoz Peterlin
PURPOSE: The influence of the Integral Quality Monitor (IQM) transmission detector on photon beam properties was evaluated in a preclinical phase, using data from nine participating centres: (i) the change of beam quality (beam hardening), (ii) the influence on surface dose, and (iii) the attenuation of the IQM detector. METHODS: For 6 different nominal photon energies (4 standard, 2 FFF) and square field sizes from 1×1cm(2) to 20×20cm(2), the effect of IQM on beam quality was assessed from the PDD20,10 values obtained from the percentage dose depth (PDD) curves, measured with and without IQM in the beam path...
March 20, 2017: Zeitschrift Für Medizinische Physik
https://www.readbyqxmd.com/read/28300376/moving-gpu-opencl-based-monte-carlo-dose-calculation-toward-clinical-use-automatic-beam-commissioning-and-source-sampling-for-treatment-plan-dose-calculation
#4
Zhen Tian, Yongbao Li, Nima Hassan-Rezaeian, Steve B Jiang, Xun Jia
We have previously developed a GPU-based Monte Carlo (MC) dose engine on the OpenCL platform, named goMC, with a built-in analytical linear accelerator (linac) beam model. In this paper, we report our recent improvement on goMC to move it toward clinical use. First, we have adapted a previously developed automatic beam commissioning approach to our beam model. The commissioning was conducted through an optimization process, minimizing the discrepancies between calculated dose and measurement. We successfully commissioned six beam models built for Varian TrueBeam linac photon beams, including four beams of different energies (6 MV, 10 MV, 15 MV, and 18 MV) and two flattening-filter-free (FFF) beams of 6 MV and 10 MV...
March 2017: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28300374/efficient-independent-planar-dose-calculation-for-fff-imrt-qa-with-a-bivariate-gaussian-source-model
#5
Feifei Li, Ji-Yeon Park, Brendan Barraclough, Bo Lu, Jonathan Li, Chihray Liu, Guanghua Yan
The aim of this study is to perform a direct comparison of the source model for photon beams with and without flattening filter (FF) and to develop an efficient independent algorithm for planar dose calculation for FF-free (FFF) intensity-modulated radiotherapy (IMRT) quality assurance (QA). The source model consisted of a point source modeling the primary photons and extrafocal bivariate Gaussian functions modeling the head scatter, monitor chamber backscatter, and collimator exchange effect. The model parameters were obtained by minimizing the difference between the calculated and measured in-air output factors (Sc )...
March 2017: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28297462/surface-dose-variations-in-6-and-10-mv-flattened-and-flattening-filter-free-fff-photon-beams
#6
Jason Cashmore
As the use of linear accelerators operating in flattening filter-free (FFF) modes becomes more widespread, it is important to have an understanding of the surface doses delivered to patients with these beams. Flattening filter removal alters the beam quality and relative contributions of low-energy X-rays and contamination electrons in the beam. Having dosimetric data to describe the surface dose and buildup regions under a range of conditions for FFF beams is important if clinical decisions are to be made...
September 2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28297340/dosimetric-properties-of-equivalent-quality-flattening-filter-free-fff-and-flattened-photon-beams-of-versa-hd-linear-accelerator
#7
Mukesh N Meshram, Srimanta Pramanik, C P Ranjith, Saravana K Gopal, Rishabh Dobhal
This study presents the basic dosimetric properties of photon beams of a Versa HD linear accelerator (linac), which is capable of delivering flattening filter-free (FFF) beams with a beam quality equivalent to the corresponding flattened beams based on comprehensive beam data measurement. The analyzed data included the PDDs, profiles, penumbra, out-of-field doses, surface doses, output factors, head and phantom scatter factors, and MLC transmissions for both FFF and flattened beams of 6 MV and 10 MV energy from an Elekta Versa HD linac...
May 2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28297327/small-field-detector-correction-factors-effects-of-the-flattening-filter-for-elekta-and-varian-linear-accelerators
#8
Madelaine K Tyler, Paul Z Y Liu, Christopher Lee, David R McKenzie, Natalka Suchowerska
Flattening filter-free (FFF) beams are becoming the preferred beam type for stereotactic radiosurgery (SRS) and stereotactic ablative radiation therapy (SABR), as they enable an increase in dose rate and a decrease in treatment time. This work assesses the effects of the flattening filter on small field output factors for 6 MV beams generated by both Elekta and Varian linear accelerators, and determines differences between detector response in flattened (FF) and FFF beams. Relative output factors were measured with a range of detectors (diodes, ionization chambers, radiochromic film, and microDiamond) and referenced to the relative output factors measured with an air core fiber optic dosimeter (FOD), a scintillation dosimeter developed at Chris O'Brien Lifehouse, Sydney...
May 2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28297306/epid-based-dosimetry-to-verify-imrt-planar-dose-distribution-for-the-as1200-epid-and-fff-beams
#9
Narges Miri, Peter Keller, Benjamin J Zwan, Peter Greer
We proposed to perform a basic dosimetry commissioning on a new imager system, the Varian aS1200 electronic portal imaging device (EPID) and TrueBeam 2.0 linear accelerator for flattened (FF) and flattening filter-free (FFF) beams, then to develop an image-based quality assurance (QA) model for verification of the system delivery accuracy for intensity-modulated radiation therapy (IMRT) treatments. For dosimetry testing, linearity of dose response with MU, imager lag, and effectiveness of backscatter shielding were investigated...
November 2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28297295/a-comparison-of-methods-for-monitoring-photon-beam-energy-constancy
#10
Song Gao, Peter A Balter, Mark Rose, William E Simon
In extension of a previous study, we compared several photon beam energy metrics to determine which was the most sensitive to energy change; in addition to those, we accounted for both the sensitivity of each metric and the uncertainty in determining that metric for both traditional flattening filter (FF) beams (4, 6, 8, and 10 MV) and for flattening filter-free (FFF) beams (6 and 10 MV) on a Varian TrueBeam. We examined changes in these energy metrics when photon energies were changed to ±5% and ±10% from their nominal energies: 1) an attenuation-based metric (the percent depth dose at 10 cm depth, PDD(10)) and, 2) profile-based metrics, including flatness (Flat) and off-axis ratios (OARs) measured on the orthogonal axes or on the diagonals (diagonal normalized flatness, FDN)...
November 2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28297290/gafchromic-ebt-xd-film-dosimetry-characterization-in-high-dose-volumetric-modulated-arc-therapy
#11
Hideharu Miura, Shuichi Ozawa, Fumika Hosono, Naoki Sumida, Toshiya Okazue, Kiyoshi Yamada, Yasushi Nagata
Radiochromic films are important tools for assessing complex dose distributions. Gafchromic EBT-XD films have been designed for optimal performance in the 40-4,000 cGy dose range. We investigated the dosimetric characteristics of these films, including their dose-response, postexposure density growth, and dependence on scanner orientation, beam energy, and dose rate with applications to high-dose volumetric-modulated arc therapy (VMAT) verification. A 10 MV beam from a TrueBeam STx linear accelerator was used to irradiate the films with doses in the 0-4,000 cGy range...
November 2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28297285/deriving-detector-specific-correction-factors-for-rectangular-small-fields-using-a-scintillator-detector
#12
Yujiao Qin, Hualiang Zhong, Ning Wen, Karen Snyder, Yimei Huang, Indrin J Chetty
The goal of this study was to investigate small field output factors (OFs) for flattening filter-free (FFF) beams on a dedicated stereotactic linear accelerator-based system. From this data, the collimator exchange effect was quantified, and detector-specific correction factors were generated. Output factors for 16 jaw-collimated small fields (from 0.5 to 2 cm) were measured using five different detectors including an ion chamber (CC01), a stereotactic field diode (SFD), a diode detector (Edge), Gafchromic film (EBT3), and a plastic scintillator detector (PSD, W1)...
November 2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28297283/clinically-relevant-investigation-of-flattening-filter-free-skin-dose
#13
Christopher L Guy, Kishor Karki, Manju Sharma, Siyong Kim
As flattening filter-free (FFF) photon beams become readily available for treatment delivery in techniques such as SBRT, thorough investigation of skin dose from FFF photon beams is necessary under clinically relevant conditions. Using a parallel-plate PTW Markus chamber placed in a custom water-equivalent phantom, surface-dose measurements were taken at 2×2,3×3,4×4,6×6,8×8,10×10,20×20, and 30×30 cm2 field sizes, at 80, 90, and 100 cm source-to-surface distances (SSDs), and with fields defined by jaws and multileaf collimator (MLC) using multiple beam energies (6X, 6XFFF, 10X, and 10XFFF)...
November 2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28296305/on-flattening-filter-free-portal-dosimetry
#14
Eduardo Pardo, Juan Castro Novais, María Yolanda Molina López, Sheila Ruiz Maqueda
Varian introduced (in 2010) the option of removing the flattening filter (FF) in their C-Arm linacs for intensity-modulated treatments. This mode, called flattening filter-free (FFF), offers the advantage of a greater dose rate. Varian's "Portal Dosimetry" is an electronic portal imager device (EPID)-based tool for IMRT verification. This tool lacks the capability of verifying flattening filter-free (FFF) modes due to saturation and lack of an image prediction algorithm. (Note: the latest versions of this software and EPID correct these issues...
July 2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28291940/superficial-and-peripheral-dose-in-compensator-based-fff-beam-imrt
#15
Daniel G Zhang, Vladimir Feygelman, Eduardo G Moros, Kujtim Latifi, Sarah Hoffe, Jessica Frakes, Geoffrey G Zhang
Flattening filter-free (FFF) beams produce higher dose rates. Combined with compensator-based intensity modulated radiotherapy (IMRT) techniques, the dose delivery for each beam can be much shorter compared to the flattened beam MLC-based or flattened beam compensator-based IMRT. This 'snap shot' IMRT delivery is beneficial to patients for tumor motion management. Due to softer energy, superficial doses in FFF beam treatment are usually higher than those from flattened beams. Due to no flattening filter, thus less photon scattering, peripheral doses are usually lower in FFF beam treatment...
January 2017: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28291939/pixel-response-based-epid-dosimetry-for-patient-specific-qa
#16
Bin Han, Aiping Ding, Minghui Lu, Lei Xing
Increasing use of high dose rate, flattening filter free (FFF), and/or small-sized field beams presents a significant challenge to the medical physics community. In this work, we develop a strategy of using a high spatial resolution and high frame rate amorphous silicon flat panel electronic portal imaging device (EPID) for dosimetric measurements of these challenging cases, as well as for conventional external beam therapy. To convert a series of raw EPID-measured radiation field images into water-based dose distribution, a pixel-to-pixel dose-response function of the EPID specific to the linac is essential...
January 2017: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28291921/evaluation-of-the-truebeam-machine-performance-check-mpc-beam-constancy-checks-for-flattened-and-flattening-filter-free-fff-photon-beams
#17
Michael P Barnes, Peter B Greer
Machine Performance Check (MPC) is an automated and integrated image-based tool for verification of beam and geometric performance of the TrueBeam linac. The aims of the study were to evaluate the MPC beam performance tests against current daily quality assurance (QA) methods, to compare MPC performance against more accurate monthly QA tests and to test the sensitivity of MPC to changes in beam performance. The MPC beam constancy checks test the beam output, uniformity, and beam center against the user defined baseline...
January 2017: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28291919/an-in-house-protocol-for-improved-flood-field-calibration-of-truebeam-fff-cine-imaging
#18
Austin M Faught, Fang-Fang Yin, Justus Adamson
PURPOSE: TrueBeams equipped with the 40 × 30 cm(2) Electronic Portal Imaging Devices (EPIDs) are prone to image saturation at the image center when used with flattening filter free (FFF) photon energies. While cine imaging during treatment may not saturate because the beam is attenuated by the patient, the flood field calibration is affected when the standard calibration procedure is followed. Here, we describe the hardware and protocol to achieve improved image quality for this model of TrueBeam EPID...
January 2017: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28261817/field-correction-factors-for-a-ptw-31016-pinpoint-ionization-chamber-for-both-flattened-and-unflattened-beams-study-of-the-main-sources-of-uncertainties
#19
Josep Puxeu Vaqué, M Amor Duch Guillen, William H Nailon, M Cruz Lizuain Arroyo, Mercè Ginjaume
PURPOSE: The primary aim of this study was to determine correction factors, kQclin,Qmsr,fclin,fmsr for a PTW-31016 ionization chamber on field sizes from 0.5 cm x 0.5 cm to 2 cm x 2 cm for both flattened (FF) and flattened filter-free (FFF) beams produced in a TrueBeam clinical accelerator. The secondary objective was the determination of field output factors, ΩQclin,Qmsrfclin,fmsr, over this range of field sizes using both Monte Carlo (MC) simulation and measurements. METHODS: kQclin,Qmsrfclin,fmsr for the PTW-31016 chamber were calculated by MC simulation for field sizes of 0...
March 6, 2017: Medical Physics
https://www.readbyqxmd.com/read/28256932/understanding-the-working-relationships-between-national-health-service-clinicians-and-finance-staff
#20
Virginia Minogue, Rebecca McCaffry
Purpose The Department of Health and the National Health Service (NHS) Future Focused Finance (FFF) programme promotes effective engagement between clinical and finance staff. Surveys undertaken by the Department of Health between 2013 and 2015 found few NHS Trusts reported high levels of engagement. The purpose of this paper is to gain a better understanding of current working relationships between NHS clinical and finance professionals and how they might be supported to become more effective. Design/methodology/approach Ipsos MORI were commissioned by the NHS FFF programme to undertake an online survey of NHS clinical and finance staff between June and August 2015...
March 13, 2017: International Journal of Health Care Quality Assurance
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