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https://www.readbyqxmd.com/read/28714454/a-back-projection-algorithm-in-the-presence-of-an-extra-attenuating-medium-towards-epid-dosimetry-for-the-mr-linac
#1
I Torres-Xirau, I Olaciregui-Ruiz, R A Rozendaal, P González, B J Mijnheer, J-J Sonke, U A van der Heide, A Mans
In external beam radiotherapy, electronic portal imaging devices (EPIDs) are frequently used for pre-treatment and for in vivo dose verification. Currently, various MR-guided radiotherapy systems are being developed and clinically implemented. Independent dosimetric verification is highly desirable. For this purpose we adapted our EPID-based dose verification system for use with the MR-Linac combination developed by Elekta in cooperation with UMC Utrecht and Philips. In this study we extended our back-projection method to cope with the presence of an extra attenuating medium between the patient and the EPID...
July 17, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28711480/commissioning-of-small-field-size-radiosurgery-cones-in-a-6-mv-flattening-filter-free-beam
#2
Juan Diego Azcona, Benigno Barbés, Verónica Morán, Javier Burguete
This study aimed to describe the commissioning of small field size radiosurgery cones in a 6-MV flattening filter free (FFF) beam and report our measured values. Four radiosurgery cones of diameters 5, 10, 12.5, and 15 mm supplied by Elekta Medical were commissioned in a 6-MV FFF beam from an Elekta Versa linear accelerator. The extraction of a reference signal for measuring small fields in scanning mode is challenging. A transmission chamber was attached to the lower part of the collimators and used for percentage depth dose (PDD) and profile measurements in scanning mode with a stereotactic diode...
July 12, 2017: Medical Dosimetry: Official Journal of the American Association of Medical Dosimetrists
https://www.readbyqxmd.com/read/28688120/electron-beam-water-calorimetry-measurements-to-obtain-beam-quality-conversion-factors
#3
Bryan R Muir, Claudiu D Cojocaru, Malcolm R McEwen, Carl K Ross
PURPOSE: To provide results of water calorimetry and ion chamber measurements in high-energy electron beams carried out at the National Research Council Canada (NRC). There are three main aspects to this work: 1) investigation of the behavior of ionization chambers in electron beams of different energies with focus on long-term stability, 2) water calorimetry measurements to determine absorbed dose to water in high-energy beams for direct calibration of ion chambers, and 3) using measurements of chamber response relative to reference ion chambers, determination of beam quality conversion factors, kQ, for several ion chamber types...
July 8, 2017: Medical Physics
https://www.readbyqxmd.com/read/28679448/simultaneous-integrated-boost-therapy-of-carcinoma-of-the-hypopharynx-larynx-with-and-without-flattening-filter-a-treatment-planning-and-dosimetry-study
#4
Barbara Dobler, Tina Obermeier, Matthias G Hautmann, Amine Khemissi, Oliver Koelbl
BACKGROUND: The aim of this study was to investigate if the flattening filter free (FFF) irradiation mode of a linear accelerator (linac) is advantageous as compared to the flat beam (FF) irradiation mode in intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for carcinoma of the hypopharynx / larynx. METHODS: Four treatment plans were created for each of 10 patients for an Elekta Synergy linac with Agility collimating device, a dual arc VMAT and a nine field step and shoot IMRT each with and without flattening filter...
July 5, 2017: Radiation Oncology
https://www.readbyqxmd.com/read/28669539/monte-carlo-dosimetric-characterization-of-the-flexisource-co-60-high-dose-rate-brachytherapy-source-using-penelope
#5
Julio F Almansa, Rafael Guerrero, Javier Torres, Antonio M Lallena
PURPOSE: (60)Co sources have been commercialized as an alternative to (192)Ir sources for high-dose-rate (HDR) brachytherapy. One of them is the Flexisource Co-60 HDR source manufactured by Elekta. The only available dosimetric characterization of this source is that of Vijande et al. [J Contemp Brachytherapy 2012; 4:34-44], whose results were not included in the AAPM/ESTRO consensus document. In that work, the dosimetric quantities were calculated as averages of the results obtained with the Geant4 and PENELOPE Monte Carlo (MC) codes, though for other sources, significant differences have been quoted between the values obtained with these two codes...
June 29, 2017: Brachytherapy
https://www.readbyqxmd.com/read/28644913/supplement-2-for-the-2004-update-of-the-aapm-task-group-no-43-report-joint-recommendations-by-the-aapm-and-gec-estro
#6
Mark J Rivard, Facundo Ballester, Wayne M Butler, Larry A DeWerd, Geoffrey S Ibbott, Ali S Meigooni, Christopher S Melhus, Michael G Mitch, Ravinder Nath, Panagiotis Papagiannis
Since publication of the 2004 update to the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report (TG-43U1) and its 2007 supplement (TG-43U1S1), several new low-energy photon-emitting brachytherapy sources have become available. Many of these sources have satisfied the AAPM prerequisites for routine clinical purposes and are posted on the Brachytherapy Seed Registry managed jointly by the AAPM and the Imaging and Radiation Oncology Core Houston Quality Assurance Center (IROC Houston)...
June 23, 2017: Medical Physics
https://www.readbyqxmd.com/read/28640950/development-of-a-monte-carlo-multiple-source-model-for-inclusion-in-a-dose-calculation-auditing-tool
#7
Austin M Faught, Scott E Davidson, Jonas Fontenot, Stephen F Kry, Carol Etzel, Geoffrey S Ibbott, David S Followill
PURPOSE: The Imaging and Radiation Oncology Core Houston (IROC-H) (formerly the Radiological Physics Center) has reported varying levels of agreement in their anthropomorphic phantom audits. There is reason to believe one source of error in this observed disagreement is the accuracy of the dose calculation algorithms and heterogeneity corrections used. To audit this component of the radiotherapy treatment process an independent dose calculation tool is needed. METHODS: Monte Carlo multiple source models for Elekta 6MV and 10MV therapeutic x-ray beams were commissioned based on measurement of central axis depth dose data for a 10 x 10 cm(2) field size and dose profiles for a 40 x 40 cm(2) field size...
June 22, 2017: Medical Physics
https://www.readbyqxmd.com/read/28636763/sensitive-volume-effects-on-monte-carlo-calculated-ion-chamber-response-in-magnetic-fields
#8
Victor N Malkov, D W O Rogers
PURPOSE: The development of magnetic resonance-guided radiation therapy (MRgRT) necessitates accurate Monte Carlo (MC) models of ion chambers for computing ion chamber corrections to compensate for the presence of the magnetic field. This study evaluates the sensitivity of the ion chamber dose response in a magnetic field on the collection volume used in the MC simulation. METHODS: The EGSnrc system's egs_chamber application is used with a recently developed and validated magnetic field transport code...
June 21, 2017: Medical Physics
https://www.readbyqxmd.com/read/28635617/the-dosimetric-impact-of-gadolinium-based-contrast-media-in-gbm-brain-patient-plans-for-a-mri-linac
#9
Syed Bilal Ahmad, Moti Raj Paudel, Arman Sarfehnia, Anthony Kim, Geordi Pang, Mark Ruschin, Arjun Sahgal, Brian M Keller
Dosimetric effects of gadolinium based contrast media (Gadovist) were evaluated for the Elekta MRI Linear accelerator (MRL) using the research version of Monaco treatment planning system (TPS). In order to represent a gadolinium uptake it was manually assigned to a phantom as well as to the Gross Tumour Volume (GTV) of 6 Glioblastoma Multiforme (GBM) patients. A preliminary estimate of dose enhancement, due to gadolinium, was performed using the phantom irradiated with a single beam. More complicated assessment was performed for the GBM patients using a 7 field IMRT technique...
June 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28624329/the-bebig-valencia-type-skin-applicators-dosimetric-study-and-implementation-of-a-dosimetric-hybrid-technique
#10
Georgios Anagnostopoulos, Michael Andrássy, Dimos Baltas
PURPOSE: To determine the relative dose rate distribution in water for the Bebig 20 mm and 30 mm skin applicators and report results in a form suitable for potential clinical use. Results for both skin applicators are also provided in the form of a hybrid Task Group 43 (TG-43) dosimetry technique. Furthermore, the radiation leakage around both skin applicators from the radiation protection point of view and the impact of the geometrical source position uncertainties are studied and reported...
June 14, 2017: Brachytherapy
https://www.readbyqxmd.com/read/28597229/couch-modelling-for-volumetric-modulated-arc-therapy-vmat
#11
Te-Yu Chyou, Friedlieb Lorenz
The aim of this work was to investigate the impact of the accuracy of a certain couch model on the overall accuracy of the dose calculation. For this purpose two models of the Varian Exact Couch (Varian Medical Systems, Palo Alto, CA, USA) for use in the planning of volumetric modulated arc therapy (VMAT) were created in Monaco 5.1 (Elekta, Stockholm, Sweden). The first was a simplistic model, with the relative electron densities (ED) of structures based entirely on CT Hounsfield units (HU). The second couch model was obtained by assigning the appropriate EDs to the relevant couch structures...
June 2017: Australasian Physical & Engineering Sciences in Medicine
https://www.readbyqxmd.com/read/28541190/benchmarking-for-on-scalp-meg-sensors
#12
Minshu Xie, Justin F Schneiderman, Maxim L Chukharkin, Alexei Kalabukhov, Bushra Riaz, Daniel Lundqvist, Stephen Whitmarsh, Matti Hamalainen, Veikko Jousmaki, Robert Oostenveld, Dag Winkler
OBJECTIVE: We present a benchmarking protocol for quantitatively comparing emerging on-scalp magnetoencephalography (MEG) sensor technologies to their counterparts in state-of-the-art MEG systems. METHODS: As a means of validation, we compare a high-critical-temperature superconducting quantum interference device (high Tc SQUID) with the low- Tc SQUIDs of an Elekta Neuromag TRIUX system in MEG recordings of auditory and somatosensory evoked fields (SEFs) on one human subject...
June 2017: IEEE Transactions on Bio-medical Engineering
https://www.readbyqxmd.com/read/28536486/emerging-indications-for-fractionated-gamma-knife-radiosurgery
#13
Emory McTyre, Corbin A Helis, Michael Farris, Lisa Wilkins, Darrell Sloan, William H Hinson, J Daniel Bourland, William A Dezarn, Michael T Munley, Kounosuke Watabe, Fei Xing, Adrian W Laxton, Stephen B Tatter, Michael D Chan
BACKGROUND: Gamma Knife radiosurgery (GKRS) allows for the treatment of intracranial tumors with a high degree of dose conformality and precision. There are, however, certain situations wherein the dose conformality of GKRS is desired, but single session treatment is contraindicated. In these situations, a traditional pin-based GKRS head frame cannot be used, as it precludes fractionated treatment. OBJECTIVE: To report our experience in treating patients with fractionated GKRS using a relocatable, noninvasive immobilization system...
February 1, 2017: Neurosurgery
https://www.readbyqxmd.com/read/28514899/clinical-positioning-accuracy-for-multisession-stereotactic-radiotherapy-with-the-gamma-knife-perfexion
#14
Wade P Smith, Lori A Young, Mark H Phillips, Michael Cheung, Lia M Halasz, Jason K Rockhill
Multisession stereotactic radiation therapy is increasingly being seen as a preferred option for intracranial diseases in close proximity to critical structures and for larger target volumes. The objective of this study is to investigate the reproducibility of the Extend system from Elekta. A retrospective review was conducted for all patients treated with multisession Gamma Knife between July 2010 and June 2015, including both malignant and benign lesions. Eighty-four patients were treated in this 5-year span...
January 1, 2017: Technology in Cancer Research & Treatment
https://www.readbyqxmd.com/read/28508836/tabulated-square-shaped-source-model-for-linear-accelerator-electron-beam-simulation
#15
Navid Khaledi, Mahmood Reza Aghamiri, Hossein Aslian, Ahmad Ameri
CONTEXT: Using this source model, the Monte Carlo (MC) computation becomes much faster for electron beams. AIMS: The aim of this study was to present a source model that makes linear accelerator (LINAC) electron beam geometry simulation less complex. SETTINGS AND DESIGN: In this study, a tabulated square-shaped source with transversal and axial distribution biasing and semi-Gaussian spectrum was investigated. SUBJECTS AND METHODS: A low energy photon spectrum was added to the semi-Gaussian beam to correct the bremsstrahlung X-ray contamination...
January 2017: Journal of Cancer Research and Therapeutics
https://www.readbyqxmd.com/read/28503898/evaluation-of-initial-setup-errors-of-two-immobilization-devices-for-lung-stereotactic-body-radiation-therapy-sbrt
#16
Yoshihiro Ueda, Teruki Teshima, Higinia Cárdenes, Indra J Das
The aim of this study was to investigate the accuracy and efficacy of two commonly used commercial immobilization systems for stereotactic body radiation therapy (SBRT) in lung cancer. This retrospective study assessed the efficacy and setup accuracy of two immobilization systems: the Elekta Body Frame (EBF) and the Civco Body Pro-Lok (CBP) in 80 patients evenly divided for each system. A cone beam CT (CBCT) was used before each treatment fraction for setup correction in both devices. Analyzed shifts were applied for setup correction and CBCT was repeated...
May 14, 2017: Journal of Applied Clinical Medical Physics
https://www.readbyqxmd.com/read/28493295/towards-ultrasound-guided-adaptive-radiotherapy-for-cervical-cancer-evaluation-of-elekta-s-semiautomated-uterine-segmentation-method-on-3d-ultrasound-images
#17
Sarah A Mason, Tuathan P O'Shea, Ingrid M White, Susan Lalondrelle, Kate Downey, Mariwan Baker, Claus F Behrens, Jeffrey C Bamber, Emma J Harris
PURPOSE: 3D ultrasound (US) images of the uterus may be used to adapt radiotherapy (RT) for cervical cancer patients based on changes in daily anatomy. This requires accurate on-line segmentation of the uterus. The aim of this work was to assess the accuracy of Elekta's "Assisted Gyne Segmentation" (AGS) algorithm in semi-automatically segmenting the uterus on 3D transabdominal ultrasound images by comparison with manual contours. MATERIALS & METHODS: Nine patients receiving RT for cervical cancer were imaged with the 3D Clarity(®) transabdominal probe at RT planning, and 1 to 7 times during treatment...
May 10, 2017: Medical Physics
https://www.readbyqxmd.com/read/28477339/dose-discrepancy-between-planning-system-estimation-and-measurement-in-spine-stereotactic-body-radiation-therapy-a-case-report
#18
Sankar Arumugam, Megan Berry, Cesar Ochoa, Aitang Xing, Bradley Beeksma, Philip Vial
Stereotactic body radiation therapy (SBRT) to treat spinal metastases has shown excellent clinical outcomes for local control. High dose gradients wrapping around spinal cord make this treatment technically challenging. In this work, we present a spine SBRT case where a dosimetric error was identified during pre-treatment dosimetric quality assurance (QA). A patient with metastasis in T7 vertebral body consented to undergo SBRT. A dual arc volumetric modulated arc therapy plan was generated on the Pinnacle treatment planning system (TPS) with a 6 MV Elekta machine using gantry control point spacing of 4°...
May 6, 2017: Journal of Medical Imaging and Radiation Oncology
https://www.readbyqxmd.com/read/28475490/reducing-4dcbct-imaging-time-and-dose-the-first-implementation-of-variable-gantry-speed-4dcbct-on-a-linear-accelerator
#19
Ricky T O'Brien, Uros Stankovic, Jan-Jakob Sonke, Paul J Keall
Four dimensional cone beam computed tomography (4DCBCT) uses a constant gantry speed and imaging frequency that are independent of the patient's breathing rate. Using a technique called respiratory motion guided 4DCBCT (RMG-4DCBCT), we have previously demonstrated that by varying the gantry speed and imaging frequency, in response to changes in the patient's real-time respiratory signal, the imaging dose can be reduced by 50-70%. RMG-4DCBCT optimally computes a patient specific gantry trajectory to eliminate streaking artefacts and projection clustering that is inherent in 4DCBCT imaging...
May 5, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28454327/stereotactic-radiotherapy-in-the-treatment-of-local-recurrences-of-esophageal-cancer
#20
Marcel Matzenauer, David Vrána, Zuzana Vlachová, Rene Aujesky, Radek Vrba, Cestmir Neoral, Bohuslav Melichar
Esophageal cancer (EC) consists of tumors with a generally poor prognosis, and treatment options for patients with disease recurrence are extremely limited. Due to this poor patient prognosis, the possible treatment toxicity should be carefully balanced against its potential benefit and patient quality of life. Stereotactic body radiotherapy (SBRT) is a rapidly expanding novel technique combining a short treatment time together with high local efficacy and an acceptable toxicity profile. There are no publications thus far presenting data regarding the usage of SBRT utilizing a conventional linear accelerator in locally recurrent EC patients...
March 2017: Oncology Letters
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