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Medical Physics

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https://www.readbyqxmd.com/read/29791029/development-of-a-3d-ultrasound-guidance-system-for-permanent-breast-seed-implantation
#1
Justin Michael, Daniel Morton, Deidre Batchelar, Michelle Hilts, Juanita Crook, Aaron Fenster
PURPOSE: Permanent breast seed implantation (PBSI) is a promising radiotherapy technique for early-stage breast cancer, completed in a single visit by permanently implanting 103 Pd seeds using needles inserted through a template and guided by 2D ultrasound (US). However, operator dependence has been highlighted as a limitation of this procedure. Consequently, we propose and have developed an intraoperative guidance system using 3D US and an instrumented mechanical arm to provide intraoperative 3D imaging and needle template tracking...
May 23, 2018: Medical Physics
https://www.readbyqxmd.com/read/29790174/an-update-of-nih-research-funding-of-aapm-members-from-1985-to-2017
#2
Brendan Whelan
Excellence in scientific research is one of the three pillars of the AAPMs mission to advance medicine, along with excellence in education and professional practice. The primary funder of medical research in the USA is the National Institutes of Health (NIH), which in 2017 had a budget of $33 billion USD. The Working Group for a Research Database (WGRD) previously published a special report into the development and testing of an algorithm to create a database of NIH funding of AAPM members [1]. The published data covered the years 1985 to 2015...
May 23, 2018: Medical Physics
https://www.readbyqxmd.com/read/29788552/an-analytical-dose-averaged-let-calculation-algorithm-considering-the-off-axis-let-enhancement-by-secondary-protons-for-spot-scanning-proton-therapy
#3
Shusuke Hirayama, Taeko Matsuura, Ueda Hideaki, Yusuke Fujii, Takaaki Fujii, Seishin Takao, Naoki Miyamoto, Shinichi Shimizu, Rintaro Fujimoto, Kikuo Umegaki, Hiroki Shirato
PURPOSE: To evaluate the biological effects of proton beams as part of daily clinical routine, fast and accurate calculation of dose-averaged linear energy transfer (LETd ) is required. In this study, we have developed the analytical LETd calculation method based on the pencil-beam algorithm (PBA) considering the off-axis enhancement by secondary protons. This algorithm (PBA-dLET) was then validated using Monte Carlo simulation (MCS) results. METHODS: In PBA-dLET, LET values were assigned separately for each individual dose kernel based on the PBA...
May 22, 2018: Medical Physics
https://www.readbyqxmd.com/read/29786862/experimental-fluence-modulated-proton-computed-tomography-by-pencil-beam-scanning
#4
George Dedes, Robert P Johnson, Mark Pankuch, Nick Detrich, Willemijn M A Pols, Simon Rit, Reinhard W Schulte, Katia Parodi, Guillaume Landry
PURPOSE: This experimental study is aimed at demonstrating, using a simple cylindrical water phantom, the feasibility of fluence modulated proton computed tomography (FMpCT) by pencil beam scanning (PBS) proton computed tomography (pCT). METHODS: The phase II pCT prototype of the Loma Linda U. and U. C. Santa Cruz was operated using the PBS beam line of the Northwestern Medicine Chicago Proton Center. A 20x10 grid of 1.37 cm full width half maximum pencil beams (PB) equally spaced by 1 cm was used to acquire 45 projections in step and shoot mode...
May 22, 2018: Medical Physics
https://www.readbyqxmd.com/read/29786861/temporally-feathered-intensity-modulated-radiation-therapy-a-planning-technique-to-reduce-normal-tissue-toxicity
#5
Juan Carlos López Alfonso, Shireen Parsai, Nikhil Joshi, Andrew Godley, Chirag Shah, Shlomo A Koyfman, Jimmy J Caudell, Clifton D Fuller, Heiko Enderling, Jacob G Scott
PURPOSE: Intensity modulated radiation therapy (IMRT) has allowed optimization of three-dimensional spatial radiation dose distributions permitting target coverage while reducing normal tissue toxicity. However, radiation-induced normal tissue toxicity is a major contributor to patients' quality of life and often a dose-limiting factor in the definitive treatment of cancer with radiation therapy. We propose the next logical step in the evolution of IMRT using canonical radiobiological principles, optimizing the temporal dimension through which radiation therapy is delivered to further reduce radiation-induced toxicity by increased time for normal tissue recovery...
May 22, 2018: Medical Physics
https://www.readbyqxmd.com/read/29782657/phantom-clinical-and-texture-indices-evaluation-and-optimization-of-a-penalized-likelihood-image-reconstruction-method-q-clear-on-a-bgo-pet-ct-scanner
#6
Gabriel Reynés-Llompart, Cristina Gámez-Cenzano, José Luís Vercher-Conejero, Aida Sabaté-Llobera, Nahúm Calvo-Malvar, Josep M Martí-Climent
INTRODUCTION: The aim of this study was to evaluate the behavior of a penalized-likelihood image reconstruction method (Q.Clear) under different count statistics and lesion-to-background ratios (LBR) on a BGO scanner, in order to obtain an optimum penalization factor (β value) to study and optimize for different acquisition protocols and clinical goals. METHODS: Both phantom and patient images were evaluated. Data from an image quality phantom were acquired using different Lesion-to-Background ratios and acquisition times...
May 21, 2018: Medical Physics
https://www.readbyqxmd.com/read/29782653/data-driven-gating-in-pet-influence-of-respiratory-signal-noise-on-motion-resolution
#7
Florian Büther, Iris Ernst, Lynn Johann Frohwein, Joost Pouw, Klaus Peter Schäfers, Lars Stegger
PURPOSE: Data-driven gating (DDG) approaches for positron emission tomography (PET) are interesting alternatives to conventional hardware-based gating methods. In DDG, the measured PET data themselves are utilized to calculate a respiratory signal that is subsequently used for gating purposes. The success of gating is then highly dependent on the statistical quality of the PET data. In this study we investigate how this quality determines signal noise and thus motion resolution in clinical PET scans using a center-of-mass-based (COM) DDG approach, specifically with regard to motion management of target structures in future radiotherapy planning applications...
May 21, 2018: Medical Physics
https://www.readbyqxmd.com/read/29777595/a-ring-based-compensator-imrt-system-optimized-for-low-and-middle-income-countries-design-and-treatment-planning-study
#8
Jonathon Van Schelt, Daniel Smith, Nicholas Fong, Dolla Toomeh, Patricia A Sponseller, Derek W Brown, Meghan W Macomber, Nina A Mayr, Shilpen Patel, Adam Shulman, G V Subrahmanyam, K Govindarajan, Eric C Ford
PURPOSE: We propose a novel compensator-based IMRT system designed to provide a simple, reliable, and cost-effective adjunct technology, with the goal of expanding global access to advanced radiotherapy techniques. The system would employ easily-reusable tungsten bead compensators that operate independent of a gantry (e.g. mounted in a ring around the patient). Thereby the system can be retrofitted to existing linac and cobalt teletherapy units. This study explores the quality of treatment plans from the proposed system and the dependence on associated design parameters...
May 19, 2018: Medical Physics
https://www.readbyqxmd.com/read/29772081/a-photon-source-model-based-on-particle-transport-in-a-parameterized-accelerator-structure-for-monte-carlo-dose-calculations
#9
Yoshiki Ishizawa, Suguru Dobashi, Noriyuki Kadoya, Kengo Ito, Takahito Chiba, Yoshiki Takayama, Kiyokazu Sato, Ken Takeda
PURPOSE: An accurate source model of a medical linear accelerator is essential for Monte Carlo (MC) dose calculations. This study aims to propose an analytical photon source model based on particle transport in parameterized accelerator structures, focusing on a more realistic determination of linac photon spectra compared to existing approaches. METHODS: We designed the primary and secondary photon sources based on the photons attenuated and scattered by a parameterized flattening filter...
May 17, 2018: Medical Physics
https://www.readbyqxmd.com/read/29772078/evaluating-blood-clot-progression-using-magnetic-particle-spectroscopy
#10
Hafsa Khurshid, Yipeng Shi, Brent L Berwin, John B Weaver
PURPOSE: To evaluate the thrombus maturity non-invasively providing the promise of much earlier and more accurate diagnosis of diseases ranging from stroke to myocardial infarction to deep vein thrombosis. METHODS: Magnetic spectroscopy of nanoparticle Brownian rotation (MSB), a form of magnetic particle spectroscopy sensitive to Brownian rotation of magnetic nanoparticles, was used for the detection and characterization of blood clots. The nanoparticles' relaxation time was quantified by scaling the MSB spectra in frequency to match the spectra from nanoparticles in a reference state...
May 17, 2018: Medical Physics
https://www.readbyqxmd.com/read/29772077/a-feature-alignment-score-for-online-cone-beam-ct-based-image-guided-radiotherapy-for-prostate-cancer
#11
Catriona Hargrave, Timothy Deegan, Michael Poulsen, Tomasz Bednarz, Fiona Harden, Kerrie Mengersen
PURPOSE: To develop a method for scoring online cone-beam CT (CBCT)-to-planning CT image feature alignment to inform prostate image-guided radiotherapy (IGRT) decision-making. The feasibility of incorporating volume variation metric thresholds, predictive of delivering planned dose into weighted functions, was investigated. METHODS: Radiation therapists and radiation oncologists participated in workshops where they reviewed prostate CBCT-IGRT case examples and completed a paper-based survey of image feature matching practices...
May 17, 2018: Medical Physics
https://www.readbyqxmd.com/read/29772066/3d-specific-absorption-rate-estimation-from-high-intensity-focused-ultrasound-sonications-using-the-green-s-function-heat-kernel
#12
Nicholas J Freeman, Henrik Odéen, Dennis L Parker
PURPOSE: Evaluate a numerical inverse Green's function method of deriving specific absorption rates (SARs) from high intensity focused ultrasound (HIFU) sonications given tissue parameters (thermal conductivity, specific heat capacity, and mass density) and 3-D magnetic resonance imaging (MRI) temperature measurements. METHODS: SAR estimates were evaluated using simulations and MR temperature measurements from HIFU sonications. For simulations, a "true" SAR was calculated using the hybrid angular spectrum method for ultrasound simulations...
May 17, 2018: Medical Physics
https://www.readbyqxmd.com/read/29772065/isodose-feature-preserving-voxelization-ifpv-for-radiation-therapy-treatment-planning
#13
Hongcheng Liu, Lei Xing
PURPOSE: Inverse planning involves iterative optimization of a large number of parameters and is known to be a labor-intensive procedure. To reduce the scale of computation and improve characterization of isodose plan, this paper presents an isodose feature-preserving voxelization (IFPV) framework for radiation therapy applications and demonstrate an implementation of inverse planning in the IFPV domain. METHODS: A dose distribution in IFPV scheme is characterized by partitioning the voxels into subgroups according to their geometric and dosimetric values...
May 17, 2018: Medical Physics
https://www.readbyqxmd.com/read/29772064/impact-of-inter-patient-variability-on-organ-dose-estimates-according-to-mird-schema-uncertainty-and-variance-based-sensitivity-analysis
#14
Alexandra Zvereva, Florian Kamp, Helmut Schlattl, Maria Zankl, Katia Parodi
PURPOSE: Variance-based sensitivity analysis (SA) is described and applied to the radiation dosimetry model proposed by the Committee on Medical Internal Radiation Dose (MIRD) for the organ-level absorbed dose calculations in nuclear medicine. The uncertainties in the dose coefficients thus calculated are also evaluated. METHODS: A Monte Carlo approach was used to compute first-order and total-effect SA indices, which rank the input factors according to their influence on the uncertainty in the output organ doses...
May 17, 2018: Medical Physics
https://www.readbyqxmd.com/read/29772061/an-image-guided-radiotherapy-decision-support-framework-incorporating-a-bayesian-network-and-visualization-tool
#15
Catriona Hargrave, Timothy Deegan, Tomasz Bednarz, Michael Poulsen, Fiona Harden, Kerrie Mengersen
PURPOSE: To describe a Bayesian network (BN) and complementary visualization tool, that aim to support decision-making during online cone-beam computed tomography (CBCT)-based image guide radiotherapy (IGRT) for prostate cancer patients. METHODS: The BN was created to represent relationships between observed prostate, proximal seminal vesicle (PSV), bladder and rectum volume variations, an image feature alignment score (FASTV _ OAR ), delivered dose and treatment plan compliance (TPC)...
May 17, 2018: Medical Physics
https://www.readbyqxmd.com/read/29772058/technical-note-interleaved-bipolar-acquisition-and-low-rank-reconstruction-for-water-fat-separation-in-mri
#16
JaeJin Cho, HyunWook Park
PURPOSE: To acquire interleaved bipolar data and reconstruct the full data using low-rank property for water fat separation. METHODS: Bipolar acquisition suffers from issues related to gradient switching, the opposite gradient polarities, and other system imperfections, which prevent accurate water-fat separation. In this study, an interleaved bipolar acquisition scheme and a low-rank reconstruction method were proposed to reduce issues from the bipolar gradients while achieving a short imaging time...
May 17, 2018: Medical Physics
https://www.readbyqxmd.com/read/29772057/a-4d-global-respiratory-motion-model-of-the-thorax-based-on-ct-images-a-proof-of-concept
#17
H Fayad, M Gilles, T Pan, D Visvikis
PURPOSE: Respiratory motion reduces the sensitivity and specificity of medical images especially in the thoracic and abdominal areas. It may affect applications such as cancer diagnostic imaging and/or radiation therapy (RT). Solutions to this issue include modelling of the respiratory motion in order to optimize both diagnostic and therapeutic protocols. Personalised motion modeling required patient specific four dimensional (4D) imaging which in the case of 4D computed tomography (4D CT) acquisition is associated with an increased dose...
May 17, 2018: Medical Physics
https://www.readbyqxmd.com/read/29763997/technical-note-deep-learning-based-mrac-using-rapid-ultra-short-echo-time-imaging
#18
Hyungseok Jang, Fang Liu, Gengyan Zhao, Tyler Bradshaw, Alan B McMillan
PURPOSE: In this study, we explore the feasibility of a novel framework for MR-based attenuation correction for PET/MR imaging based on deep learning via convolutional neural networks, which enables fully automated and robust estimation of a pseudo CT image based on ultrashort echo time (UTE), fat, and water images obtained by a rapid MR acquisition. METHODS: MR images for MRAC are acquired using dual echo ramped hybrid encoding (dRHE), where both UTE and out-of-phase echo images are obtained within a short single acquisition (35 sec)...
May 15, 2018: Medical Physics
https://www.readbyqxmd.com/read/29763970/technical-note-experimental-verification-of-magnetic-field-induced-beam-deflection-and-bragg-peak-displacement-for-mr-integrated-proton-therapy
#19
Sonja M Schellhammer, Sebastian Gantz, Armin Lühr, Bradley M Oborn, Michael Bussmann, Aswin L Hoffmann
PURPOSE: Given its sensitivity to anatomical variations, proton therapy is expected to benefit greatly from integration with magnetic resonance imaging for on-line anatomy monitoring during irradiation. Such an integration raises several challenges, as both systems mutually interact. The proton beam will experience quasi-continuous energy loss and energy-dependent electromagnetic deflection at the same time, giving rise to a deflected beam trajectory and an altered dose distribution with a displaced Bragg peak...
May 15, 2018: Medical Physics
https://www.readbyqxmd.com/read/29763967/machine-learning-algorithms-for-outcome-prediction-in-chemo-radiotherapy-an-empirical-comparison-of-classifiers
#20
Timo M Deist, Frank J W M Dankers, Gilmer Valdes, Robin Wijsman, I-Chow Hsu, Cary Oberije, Tim Lustberg, Johan van Soest, Frank Hoebers, Arthur Jochems, Issam El Naqa, Leonard Wee, Olivier Morin, David R Raleigh, Wouter Bots, Johannes H Kaanders, José Belderbos, Margriet Kwint, Timothy Solberg, René Monshouwer, Johan Bussink, Andre Dekker, Philippe Lambin
PURPOSE: Machine learning classification algorithms (classifiers) for prediction of treatment response are becoming more popular in radiotherapy literature. General machine learning literature provides evidence in favor of some classifier families (random forest, support vector machine, gradient boosting) in terms of classification performance. The purpose of this study is to compare such classifiers specifically for (chemo)radiotherapy datasets and to estimate their average discriminative performance for radiation treatment outcome prediction...
May 15, 2018: Medical Physics
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