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https://www.readbyqxmd.com/read/27905521/evaluation-of-a-silicon-90-sr-betavoltaic-power-source
#1
Jefferson Dixon, Aravindh Rajan, Steven Bohlemann, Dusan Coso, Ajay D Upadhyaya, Ajeet Rohatgi, Steven Chu, Arun Majumdar, Shannon Yee
Betavoltaic energy converters (i.e., β-batteries) are attractive power sources because of their potential for high energy densities (>200 MWh/kg) and long duration continuous discharge (>1 year). However, conversion efficiencies have been historically low (<3%). High efficiency devices can be achieved by matching β-radiation transport length scales with the device physics length scales. In this work, the efficiency of c-Si devices using high-energy (>1 MeV) electrons emitted from (90)Sr as a power source is investigated...
December 1, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27816362/experimental-platform-for-ultra-high-dose-rate-flash-irradiation-of-small-animals-using-a-clinical-linear-accelerator
#2
Emil Schüler, Stefania Trovati, Gregory King, Frederick Lartey, Marjan Rafat, Manuel Villegas, A Joe Praxel, Billy W Loo, Peter G Maxim
PURPOSE: A key factor limiting the effectiveness of radiation therapy is normal tissue toxicity, and recent preclinical data have shown that ultra-high dose rate irradiation (>50 Gy/s, "FLASH") potentially mitigates this effect. However, research in this field has been strongly limited by the availability of FLASH irradiators suitable for small animal experiments. We present a simple methodologic approach for FLASH electron small animal irradiation with a clinically available linear accelerator (LINAC)...
September 20, 2016: International Journal of Radiation Oncology, Biology, Physics
https://www.readbyqxmd.com/read/27685106/is-the-dose-distribution-distorted-in-imrt-and-rapidarc-treatment-when-patient-plans-are-swapped-across-beam-matched-machines
#3
Krishnappan Chockkalingam, Chandrasekaran Anu Radha, Vendhan Subramani, Vendhan Subramani, Madhan Kumar Gunasekaran
The purpose of this study is to evaluate the degree of dose distribution distortion in advanced treatments like IMRT and RapidArc when patient plans are swapped across dosimetrically equivalent so-called "beam-matched" machines. For this purpose the entire work is divided into two stages. At forefront stage all basic beam properties of 6 MV X-rays like PDD, profiles, output factors, TPR20/10 and MLC transmission of two beam-matched machines - Varian Clinac iX and Varian 600 C/D Unique - are compared and evaluated for differences...
2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/27455486/clinical-implications-of-the-overshoot-effect-for-treatment-plan-delivery-and-patient-specific-quality-assurance-for-step-and-shoot-imrt
#4
John Baines, Sylwia J Zawlodzka, Matthew L Parfitt, Brigid E Hickey, Andrew P Pullar
In this work, overshoot and undershoot effects associated with step-and-shoot IMRT (SSIMRT) delivery on a Varian Clinac 21iX are investigated, and their impact on patient-specific QA point dose measurements and treatment plan delivery are evaluated. Pinnacle3 SSIMRT plans consisting of 5, 10, and 15 identical 5 × 5 cm2 MLC defined segments and MU/segment values of 5 MU, 10 MU, and 20 MU were utilized and delivered at 600/300 MU/min. Independent of the number of segments the overshoot and undershoot at 600 MU/min were approximately ± 10%, ± 5%, and ± 2...
2016: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/27170731/on-the-neutron-radiation-field-and-air-activation-around-a-medical-electron-linac
#5
Felix Horst, Georg Fehrenbacher, Klemens Zink
In high-energy photon therapy, several radiation protection issues result from photonuclear reactions. In this study, the photoneutron radiation field around a Varian Clinac linear accelerator in 18 MV-X mode within two different radiotherapy bunkers was investigated by means of Monte Carlo simulations using the FLUKA code as well as ambient dose-equivalent measurements. Furthermore, the activation of the air inside the treatment room due to photonuclear reactions ((13)N and (15)O) and the capture of photoneutrons moderated down within the bunker ((41)Ar) was studied by FLUKA simulations...
May 11, 2016: Radiation Protection Dosimetry
https://www.readbyqxmd.com/read/27072390/the-use-of-log-file-analysis-within-vmat-audits
#6
Conor K McGarry, Christina E Agnew, Mohammad Hussein, Yatman Tsang, Alan R Hounsell, Catharine H Clark
OBJECTIVE: This work investigated the delivery accuracy of different Varian linear accelerator models using log file-derived multileaf collimator (MLC) root mean square (RMS) values. METHODS: Seven centres independently created a plan on the same virtual phantom using their own planning system, and the log files were analyzed following delivery of the plan in each centre to assess MLC positioning accuracy. A single standard plan was also delivered by the seven centres to remove variations in complexity, and the log files were analyzed for Varian TrueBeams and Clinacs (2300IX or 2100CD models)...
June 2016: British Journal of Radiology
https://www.readbyqxmd.com/read/27052438/raystation-monte-carlo-application-evaluation-of-electron-calculations-with-entry-obliquity
#7
Ben Archibald-Heeren, Guilin Liu
To evaluate the accuracy of Raystation's implementation for Monte Carlo VMC ++ with electrons at varying angles of incidence for low and medium energy electron beams. Thirty-two profile and percentage depth dose scans were taken at 5° incident angle intervals for 6 and 12 MeV and compared to extracted fluences from Raystation calculations using gamma analysis with 2 %/2 mm criteria. Point dose measurements were compared to calculated doses to determine output accuracy. Electron profile and percentage depth dose curves for both energies show good agreement between 0° and 20° with 29/30 scans above 90 % pass rate...
June 2016: Australasian Physical & Engineering Sciences in Medicine
https://www.readbyqxmd.com/read/27008349/robust-breathing-signal-extraction-from-cone-beam-ct-projections-based-on-adaptive-and-global-optimization-techniques
#8
Ming Chao, Jie Wei, Tianfang Li, Yading Yuan, Kenneth E Rosenzweig, Yeh-Chi Lo
We present a study of extracting respiratory signals from cone beam computed tomography (CBCT) projections within the framework of the Amsterdam Shroud (AS) technique. Acquired prior to the radiotherapy treatment, CBCT projections were preprocessed for contrast enhancement by converting the original intensity images to attenuation images with which the AS image was created. An adaptive robust z-normalization filtering was applied to further augment the weak oscillating structures locally. From the enhanced AS image, the respiratory signal was extracted using a two-step optimization approach to effectively reveal the large-scale regularity of the breathing signals...
April 21, 2016: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/26831923/investigation-of-conformal-and-intensity-modulated-radiation-therapy-techniques-to-determine-the-absorbed-fetal-dose-in-pregnant-patients-with-breast-cancer
#9
Akın Öğretici, Uğur Akbaş, Canan Köksal, Hatice Bilge
The aim of this research was to investigate the fetal doses of pregnant patients undergoing conformal radiotherapy or intensity-modulated radiation therapy (IMRT) for breast cancers. An Alderson Rando phantom was chosen to simulate a pregnant patient with breast cancer who is receiving radiation therapy. This phantom was irradiated using the Varian Clinac DBX 600 system (Varian Medical System, Palo Alto, CA) linear accelerator, according to the standard treatment plans of both three-dimensional conformal radiation therapy (3-D CRT) and IMRT techniques...
2016: Medical Dosimetry: Official Journal of the American Association of Medical Dosimetrists
https://www.readbyqxmd.com/read/26457404/evaluation-of-lens-absorbed-dose-with-cone-beam-igrt-procedures
#10
R Palomo, M C Pujades, J Gimeno-Olmos, V Carmona, F Lliso, C Candela-Juan, J Vijande, F Ballester, J Perez-Calatayud
The purpose of this work is to evaluate the absorbed dose to the eye lenses due to the cone beam computed tomography (CBCT) system used to accurately position the patient during head-and-neck image guided procedures. The on-board imaging (OBI) systems (v.1.5) of Clinac iX and TrueBeam (Varian) accelerators were used to evaluate the imparted dose to the eye lenses and some additional points of the head. All CBCT scans were acquired with the Standard-Dose Head protocol from Varian. Doses were measured using thermoluminescence dosimeters (TLDs) placed in an anthropomorphic phantom...
December 2015: Journal of Radiological Protection: Official Journal of the Society for Radiological Protection
https://www.readbyqxmd.com/read/26219015/comparison-of-measured-varian-clinac-21ex-and-truebeam-accelerator-electron-field-characteristics
#11
COMPARATIVE STUDY
Samantha A M Lloyd, Sergei Zavgorodni, Isabelle M Gagne
Dosimetric comparisons of radiation fields produced by Varian's newest linear accelerator, the TrueBeam, with those produced by older Varian accelerators are of interest from both practical and research standpoints. While photon fields have been compared in the literature, similar comparisons of electron fields have not yet been reported. In this work, electron fields produced by the TrueBeam are compared with those produced by Varian's Clinac 21EX accelerator. Diode measurements were taken of fields shaped with electron applicators and delivered at 100 cm SSD, as well as those shaped with photon MLCs without applicators and delivered at 70 cm SSD for field sizes ranging from 5 × 5 to 25 × 25 cm² at energies between 6 and 20 MeV...
2015: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/26218999/determining-the-optimal-dosimetric-leaf-gap-setting-for-rounded-leaf-end-multileaf-collimator-systems-by-simple-test-fields
#12
Weiguang Yao, Jonathan B Farr
Individual QA for IMRT/VMAT plans is required by protocols. Sometimes plans cannot pass the institute's QA criteria. For the Eclipse treatment planning system (TPS) with rounded leaf-end multileaf collimator (MLC), one practical way to improve the agreement of planned and delivered doses is to tune the value of dosimetric leaf gap (DLG) in the TPS from the measured DLG. We propose that this step may be necessary due to the complexity of the MLC system, including dosimetry of small fields and the tongue-and-groove (T&G) effects, and report our use of test fields to obtain linac-specific optimal DLGs in TPSs...
2015: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/26133618/development-of-an-accurate-epid-based-output-measurement-and-dosimetric-verification-tool-for-electron-beam-therapy
#13
Aiping Ding, Lei Xing, Bin Han
PURPOSE: To develop an efficient and robust tool for output measurement and absolute dose verification of electron beam therapy by using a high spatial-resolution and high frame-rate amorphous silicon flat panel electronic portal imaging device (EPID). METHODS: The dosimetric characteristics of the EPID, including saturation, linearity, and ghosting effect, were first investigated on a Varian Clinac 21EX accelerator. The response kernels of the individual pixels of the EPID to all available electron energies (6, 9, 12, 16, and 20 MeV) were calculated by using Monte Carlo (MC) simulations, which formed the basis to deconvolve an EPID raw images to the incident electron fluence map...
July 2015: Medical Physics
https://www.readbyqxmd.com/read/26127040/technical-note-study-of-the-electron-transport-parameters-used-in-penelope-for-the-monte-carlo-simulation-of-linac-targets
#14
Miguel Rodriguez, Josep Sempau, Lorenzo Brualla
PURPOSE: The Monte Carlo simulation of electron transport in Linac targets using the condensed history technique is known to be problematic owing to a potential dependence of absorbed dose distributions on the electron step length. In the PENELOPE code, the step length is partially determined by the transport parameters C1 and C2. The authors have investigated the effect on the absorbed dose distribution of the values given to these parameters in the target. METHODS: A monoenergetic 6...
June 2015: Medical Physics
https://www.readbyqxmd.com/read/25873196/investigating-in-field-and-out-of-field-neutron-contamination-in-high-energy-medical-linear-accelerators-based-on-the-treatment-factors-of-field-size-depth-beam-modifiers-and-beam-type
#15
Fatih Biltekin, Mete Yeginer, Gokhan Ozyigit
PURPOSE: We analysed the effects of field size, depth, beam modifier and beam type on the amount of in-field and out-of-field neutron contamination for medical linear accelerators (linacs). METHODS: Measurements were carried out for three high-energy medical linacs of Elekta Synergy Platform, Varian Clinac DHX High Performance and Philips SL25 using bubble detectors. The photo-neutron measurements were taken in the first two linacs with 18 MV nominal energy, whereas the electro-neutrons were measured in the three linacs with 9 MeV, 10 MeV, 15 MeV and 18 MeV...
July 2015: Physica Medica: PM
https://www.readbyqxmd.com/read/25813482/preliminary-testing-of-gan-based-dosimeters-for-electron-beam-radiotherapy
#16
A Ismail, R Wang, A Chaikh, P Pittet, J Balosso
The response of an implantable in vivo dosimetric system based on gallium nitride radioluminescence was investigated for electron beam radiotherapy using ELEKTA SLi and VARIAN Clinac 2100 CD Linear Accelerators. A bi-channel method has been implemented for fibre background rejection. The percentage depth dose (PDD) profiles were measured in polymethyl methacrylate for 6, 12 and 18 MeV electron beams. The PDD results were in excellent agreement with those measured with reference to ionisation chambers.
July 2015: Radiation Protection Dosimetry
https://www.readbyqxmd.com/read/25404493/applicability-of-self-activation-of-an-nai-scintillator-for-measurement-of-photo-neutrons-around-a-high-energy-x-ray-radiotherapy-machine
#17
Genichiro Wakabayashi, Akihiro Nohtomi, Eriko Yahiro, Toshioh Fujibuchi, Junichi Fukunaga, Yoshiyuki Umezu, Yasuhiko Nakamura, Katsumasa Nakamura, Makoto Hosono, Tetsuo Itoh
The applicability of the activation of an NaI scintillator for neutron monitoring at a clinical linac was investigated experimentally. Thermal neutron fluence rates are derived by measurement of the I-128 activity generated in an NaI scintillator irradiated by neutrons; β-rays from I-128 are detected efficiently by the NaI scintillator. In order to verify the validity of this method for neutron measurement, we irradiated an NaI scintillator at a research reactor, and the neutron fluence rate was estimated...
January 2015: Radiological Physics and Technology
https://www.readbyqxmd.com/read/25325343/electron-beam-quality-k-q-q0-factors-for-various-ionization-chambers-a-monte-carlo-investigation-with-penelope
#18
F Erazo, L Brualla, A M Lallena
In this work we calculate the beam quality correction factor k(Q,Q0) for various plane-parallel ionization chambers. A set of Monte Carlo calculations using the code PENELOPE/PENEASY have been carried out to calculate the overall correction factor f(c,Q) for eight electron beams corresponding to a Varian Clinac 2100 C/D, with nominal energies ranging between 6 MeV and 22 MeV, for a (60)Co beam, that has been used as the reference quality Q0 and also for eight monoenergetic electron beams reproducing the quality index R50 of the Clinac beams...
November 7, 2014: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/25281945/development-of-an-expanded-field-irradiation-technique-using-a-gimbaled-x-ray-head
#19
Tomohiro Ono, Yuki Miyabe, Masahiro Yamada, Kenji Yokota, Shuji Kaneko, Akira Sawada, Hajime Monzen, Takashi Mizowaki, Masaki Kokubo, Masahiro Hiraoka
PURPOSE: The Vero4DRT has a maximum field size of 150.0 × 150.0 mm. The purpose of the present study was to develop expanded-field irradiation techniques using the unique gimbaled x-ray head of the Vero4DRT and to evaluate the dosimetric characteristics thereof. METHODS: Two techniques were developed. One features gimbal swing irradiation and multiple static segments consisting of four separate fields exhibiting 2.39° gimbal rotation around two orthogonal axes...
October 2014: Medical Physics
https://www.readbyqxmd.com/read/25190997/comparison-of-head-scatter-factor-for-6mv-and-10mv-flattened-fb-and-unflattened-fff-photon-beam-using-indigenously-designed-columnar-mini-phantom
#20
Sigamani Ashokkumar, N Arunai Nambi Raj, Sujit Nath Sinha, Girigesh Yadav, Rajesh Thiyagarajan, Kothanda Raman, Manindra Bhushan Mishra
To measure and compare the head scatter factor for flattened (FB) and unflattened (FFF) of 6MV and 10MV photon beam using indigenously designed mini phantom. A columnar mini phantom was designed as recommended by AAPM Task Group 74 with low and high atomic number materials at 10 cm (mini phantom) and at approximately twice the depth of maximum dose water equivalent thickness (brass build-up cap). Scatter in the accelerator (Sc) values of 6MV-FFF photon beams are lesser than that of the 6MV-FB photon beams (0...
July 2014: Journal of Medical Physics
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