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Medical Physics

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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
#1
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/28644905/a-realistic-phantom-for-validating-mri-based-synthetic-ct-images-of-the-human-skull
#2
Abraam S Soliman, Levi Burns, Amir Owrangi, Young Lee, William Y Song, Greg Stanisz, Brige P Chugh
PURPOSE: To introduce a new realistic human skull phantom for the validation of synthetic CT images of cortical bone from ultra-short echo-time (UTE) sequences. METHODS AND MATERIALS: A human skull of an adult female was utilized as a realistic representation of skull cortical bone. The skull was stabilized in a special acrylic container and was filled with contrast agents that have T1 and T2 relaxation times similar to human brain. The phantom was MR scanned at 3T with UTE and T2 -weighted sequences, followed by CT...
June 23, 2017: Medical Physics
https://www.readbyqxmd.com/read/28644546/-18-f-fluoromisonidazole-uptake-in-advanced-stage-non-small-cell-lung-cancer-a-voxel-by-voxel-pet-kinetics-study
#3
Daniel R McGowan, Ruth E Macpherson, Sara L Hackett, Dan Liu, Fergus V Gleeson, W Gillies McKenna, Geoff S Higgins, John D Fenwick
PURPOSE: To determine the relative abilities of compartment models to describe time-courses of 18F-fluoromisonidazole (FMISO) uptake in tumor voxels of patients with non-small cell lung cancer (NSCLC) imaged using dynamic positron emission tomography. Also to use fits of the best-performing model to investigate changes in fitted rate-constants with distance from the tumor edge. METHODS: Reversible and irreversible two- and three-tissue compartment models were fitted to 24,662 individual voxel time activity curves (TACs) obtained from tumors in 9 patients, each imaged twice...
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
#4
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/28639400/motion-estimation-for-cardiac-functional-analysis-using-two-x-ray-computed-tomography-scans
#5
George S K Fung, Luisa Ciuffo, Hiroshi Ashikaga, Katsuyuki Taguchi
PURPOSE: This work concerns computed tomography (CT)-based cardiac functional analysis (CFA) with a reduced radiation dose. As CT-CFA requires images over the entire heartbeat, the scans are often performed at 10-20% of the tube current settings that are typically used for coronary CT angiography. A large image noise then degrades the accuracy of motion estimation. Moreover, even if the scan was performed during the sinus rhythm, the cardiac motion observed in CT images may not be cyclic with patients with atrial fibrillation...
June 22, 2017: Medical Physics
https://www.readbyqxmd.com/read/28639387/determining-the-orientation-angle-of-directional-leads-for-deep-brain-stimulation-using-computed-tomography-and-digital-x-ray-imaging-a-phantom-study
#6
Alexander Sitz, Mauritius Hoevels, Alexandra Hellerbach, Andreas Gierich, Klaus Luyken, Till A Dembek, Martin Klehr, Jochen Wirths, Veerle Visser-Vandewalle, Harald Treuer
PURPOSE: Orientating the angle of directional leads for deep brain stimulation (DBS) in an axial plane introduces a new degree of freedom that is indicated by embedded anisotropic directional markers. Our aim was to develop algorithms to determine lead orientation angles from computed tomography (CT) and stereotactic x-ray imaging using standard clinical protocols, and subsequently assess the accuracy of both methods. METHODS: In CT the anisotropic marker artifact was taken as a signature of the lead orientation angle and analyzed using discrete Fourier transform of circular intensity profiles...
June 22, 2017: Medical Physics
https://www.readbyqxmd.com/read/28639302/prospective-validation-of-pathologic-complete-response-models-in-rectal-cancer-transferability-and-reproducibility
#7
Johan van Soest, Elisa Meldolesi, Ruud van Stiphout, Roberto Gatta, Andrea Damiani, Vincenzo Valentini, Philippe Lambin, Andre Dekker
PURPOSE: Multiple models have been developed to predict pathologic complete response (pCR) in locally advanced rectal cancer patients. Unfortunately, validation of these models normally omit the implications of cohort differences on prediction model performance. In this work, we will perform a prospective validation of three pCR models, including information whether this validation will target transferability or reproducibility (cohort differences) of the given models. METHODS: We applied a novel methodology, the cohort differences model, to predict whether a patient belongs to the training or to the validation cohort...
June 22, 2017: Medical Physics
https://www.readbyqxmd.com/read/28636805/a-hybrid-phantom-system-for-patient-skin-and-organ-dosimetry-in-fluoroscopically-guided-interventions
#8
David Borrego, Daniel Siragusa, Stephen Balter, Wesley E Bolch
To investigate calibrations for improved estimates of skin dose and to develop software for computing absorbed organ doses for fluoroscopically guided interventions (FGIs) with the use of radiation dose structured reports (RDSR) and the UF/NCI family of hybrid computational phantoms METHODS AND MATERIALS: Institutional review board approval was obtained for this retrospective study in which ten RDSRs were selected for their high cumulative reference air kerma values. Skin doses were computed using the University of Florida's rapid in-clinic peak skin dose algorithm (or UF-RIPSA)...
June 21, 2017: Medical Physics
https://www.readbyqxmd.com/read/28636792/mtf-and-dqe-enhancement-using-an-apodized-aperture-x-ray-detector-design
#9
Tomi F Nano, Terenz Escartin, Elina Ismailova, Karim S Karim, Jan Lindstrȍm, Ho Kyung Kim, Ian A Cunningham
PURPOSE: Acquisition of high-quality x-ray images using low patient exposures requires detectors with high detective quantum efficiency (DQE). We describe a novel apodized-aperture pixel (AAP) design that increases high-frequency modulation transfer function (MTF) and DQE values. The AAP design makes a separation of physical sensor elements from image pixels by using very small sensor elements (e.g. 0.010-0.025 mm) to synthesize desired larger image pixels (e.g. 0.1-0.2 mm). METHODS: A cascaded systems model of signal and noise propagation is developed to describe the benefits of the AAP approach in terms of the MTF, Wiener noise power spectrum (NPS) and DQE...
June 21, 2017: Medical Physics
https://www.readbyqxmd.com/read/28636778/comment-on-dosimetric-comparison-of-stopping-power-calibration-with-dual-energy-ct-and-single-energy-ct-in-proton-therapy-treatment-planning-med-phys-43-6-2845-2854-2016
#10
LETTER
Patrick Wohlfahrt, Christian Möhler, Steffen Greilich, Christian Richter
A dosimetric comparison of proton treatment planning based on single-energy CT (SECT) and dual-energy CT (DECT) was recently published by Zhu and Penfold(1) in Medical Physics. In this study, the polymer phantom Catphan Module 404 (The Phantom Laboratory, Salem, NY, USA) of known material composition was used to demonstrate an improved accuracy of dose calculation using DECT instead of SECT. To confirm this result in a more realistic human case, the authors show for a single axial CT slice the dose difference of a SECT- and DECT-based treatment plan using the anthropomorphic phantom Rando (Radiological Support Devices, Inc...
June 21, 2017: Medical Physics
https://www.readbyqxmd.com/read/28636763/sensitive-volume-effects-on-monte-carlo-calculated-ion-chamber-response-in-magnetic-fields
#11
Victor N Malkov, David W O Rogers
PURPOSE: The development of magnetic resonance guided radiation therapy (MR-gRT) 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/28636755/technical-note-combination-of-multiple-epid-imager-layers-improves-image-quality-and-tracking-performance-of-low-contrast-to-noise-objects
#12
Stephen Sf Yip, Joerg Rottmann, Haijian Chen, Daniel Morf, Rony Füglistaller, Josh Star-Lack, George Zentai, Ross Berbeco
PURPOSE: We hypothesized that combining multiple amorphous silicon flat panel layers increases photon detection efficiency in an electronic portal imaging device (EPID), improving image quality and tracking accuracy of low contrast targets during radiotherapy METHODS: The prototype imager evaluated in this study contained 4 individually programmable layers each with a copper converter layer, Gd2 O2 S scintillator and active-matrix flat panel imager (AMFPI). The imager was placed on a Varian TrueBeam linac and a Las Vegas phantom programmed with sinusoidal motion (peak-to-peak amplitude=20mm, Period=3...
June 21, 2017: Medical Physics
https://www.readbyqxmd.com/read/28627007/optical-molecular-imaging-guided-radiation-therapy-part-1-integrated-x-ray-and-bioluminescence-tomography
#13
Junwei Shi, Thirupandiyur S Udayakumar, Zhiqun Wang, Nesrin Dogan, Alan Pollack, Yidong Yang
PURPOSE: X-ray CT faces challenges in differentiating tumors from surrounding healthy tissues. A bioluminescence tomography (BLT) system which can directly reconstruct the internal luminescent tumors, was developed and integrated with CT system to accurately guide radiation dose delivery. METHODS: The BLT system, employing a lens-coupled CCD camera, was physically registered with an onboard cone beam CT system in an image guided small animal arc radiation treatment system (iSMAART)...
June 19, 2017: Medical Physics
https://www.readbyqxmd.com/read/28626978/a-fast-multi-target-inverse-treatment-planning-strategy-optimizing-dosimetric-measures-for-high-dose-rate-hdr-brachytherapy
#14
Christian V Guthier, Antonio L Damato, Akila N Viswanathan, Juergen W Hesser, Robert A Cormack
PURPOSE: In this study, we introduce a novel, fast, inverse treatment planning strategy for interstitial high-dose-rate (HDR) brachytherapy with multiple regions of interest solely based on dose-volume-histogram-related dosimetric measures (DMs). METHODS: We present a new problem formulation of the objective function that approximates the indicator variables of the standard DM optimization problem with a smooth logistic function. This problem is optimized by standard gradient-based methods...
June 19, 2017: Medical Physics
https://www.readbyqxmd.com/read/28626939/technical-note-a-3-d-rendering-algorithm-for-electromechanical-wave-imaging-of-a-beating-heart
#15
Pierre Nauleau, Lea Melki, Elaine Wan, Elisa Konofagou
PURPOSE: Arrhythmias can be treated by ablating the heart tissue in the regions of abnormal contraction. The current clinical standard provides electroanatomic 3- D maps to visualize the elec-trical activation and locate the arrhythmogenic sources. However, the procedure is time-consuming and invasive. Electromechanical Wave Imaging is an ultrasound- based non-invasive technique that can provide 2-D maps of the electromechanical activation of the heart. In order to fully visualize the complex 3-D pattern of activation, several 2-D views are acquired and processed separately They are then manually registered with a 3-D rendering software to generate a pseudo-3-D map However, this last step is operator-dependent and time-consuming...
June 19, 2017: Medical Physics
https://www.readbyqxmd.com/read/28626920/experimental-verification-of-egsnrc-monte-carlo-calculated-depth-doses-within-a-realistic-parallel-magnetic-field-in-a-polystyrene-phantom
#16
Andrei Ghila, Stephen Steciw, B Gino Fallone, Satyapal Rathee
PURPOSE: Integrating a linac with a magnetic resonance imager (MRI) will revolutionize the accuracy of external beam radiation treatments. Irradiating in the presence of a strong magnetic field, however, will modify the dose distribution. These dose modifications have been investigated previously, mainly using Monte Carlo simulations. The purpose of this work is to experimentally verify the use of the EGSnrc Monte Carlo (MC) package for calculating percent depth doses (PDDs) in a homogeneous phantom, in the presence of a realistic parallel magnetic field...
June 19, 2017: Medical Physics
https://www.readbyqxmd.com/read/28626876/optical-molecular-imaging-guided-radiation-therapy-part-2-integrated-x-ray-and-fluorescence-molecular-tomography
#17
Junwei Shi, Thirupandiyur S Udayakumar, Zhiqun Wang, Nesrin Dogan, Alan Pollack, Yidong Yang
PURPOSE: Differentiating tumor from its surrounding soft tissues is challenging for x-ray computed tomography (CT). Fluorescence molecular tomography (FMT) can directly localize the internal tumors targeted with specific fluorescent probes. A FMT system was developed and integrated onto a CT guided irradiator to improve tumor localization for image guided radiation. METHODS: The FMT system was aligned orthogonal to the cone beam CT onboard our previously developed image guided small animal arc radiation treatment system (iSMAART)...
June 19, 2017: Medical Physics
https://www.readbyqxmd.com/read/28626862/acoustic-field-characterization-of-a-clinical-magnetic-resonance-guided-high-intensity-focused-ultrasound-system-inside-the-magnet-bore
#18
Satya V V N Kothapalli, Michael B Altman, Ari Partanen, Leighton Wan, H Michael Gach, William Straube, Dennis E Hallahan, Hong Chen
PURPOSE: With the expanding clinical application of magnetic resonance-guided high intensity focused ultrasound (MR-HIFU), acoustic field characterization of MR-HIFU systems is needed for facilitating regulatory approval and ensuring consistent and safe power output of HIFU transducers. However, the established acoustic field measurement techniques typically use equipment that cannot be used in a magnetic resonance imaging (MRI) suite, thus posing a challenge to the development and execution of HIFU acoustic field characterization techniques...
June 19, 2017: Medical Physics
https://www.readbyqxmd.com/read/28622420/technical-note-comparison-of-megavoltage-dual-energy-and-single-energy-ct-based-%C3%AE-maps-for-a-4-channel-breast-coil-in-pet-mri
#19
John C Patrick, R Terry Thompson, Aaron So, John Butler, David Faul, Robert Z Stodilka, Slav Yartsev, Frank S Prato, Stewart Gaede
PURPOSE: The purpose of this study was to describe and evaluate methods for calculating a megavoltage computed tomography (MVCT) derived MR hardware attenuation map (μ-map) and dual-energy CT (DECT) for 511 keV photons. METHODS: Phantom measurements were acquired on a whole-body hybrid PET/MRI system, using a four-channel receive-only MR radiofrequency (RF) breast coil. Two acquisitions were performed: with the phantoms positioned in the four-channel RF breast coil, and without the breast coil...
June 16, 2017: Medical Physics
https://www.readbyqxmd.com/read/28622412/textural-analysis-of-early-phase-spatiotemporal-changes-in-contrast-enhancement-of-breast-lesions-imaged-with-an-ultrafast-dce-mri-protocol
#20
Jana Milenković, Mehmet Ufuk Dalmış, Janez Žgajnar, Bram Platel
PURPOSE: New ultrafast view-sharing sequences have enabled breast dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to be performed at high spatial and temporal resolution. The aim of this study is to evaluate the diagnostic potential of textural features that quantify the spatiotemporal changes of the contrast-agent uptake in computer-aided diagnosis of malignant and benign breast lesions imaged with high spatial and temporal resolution DCE-MRI. METHOD: The proposed approach is based on the textural analysis quantifying the spatial variation of six dynamic features of the early-phase contrast-agent uptake of a lesion's largest cross-sectional area...
June 16, 2017: Medical Physics
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