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Physics in Medicine and Biology

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https://www.readbyqxmd.com/read/28636564/radiation-dosimetry-in-magnetic-fields-with-farmer-type-ionization-chambers-determination-of-magnetic-field-correction-factors-for-different-magnetic-field-strengths-and-field-orientations
#1
Claudia Katharina Spindeldreier, Oliver Schrenk, Anna Bakenecker, Iwan Kawrakow, Lucas Norberto Burigo, Christian P Karger, Steffen Greilich, Asja Pfaffenberger
The aim of this work was to determine magnetic field correction factors that are needed for dosimetry in hybrid devices for MR-guided radiotherapy for Farmer-type ionization chambers for different magnetic field strengths and field orientations. The response of six custom-built Farmer-type chambers irradiated at a 6 MV linac was measured in a water tank positioned in a magnet with magnetic field strengths between 0.0 T and 1.1 T. Chamber axis, beam and magnetic field were perpendicular to each other and both magnetic field directions were investigated...
June 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28635617/the-dosimetric-impact-of-gadolinium-based-contrast-media-in-gbm-brain-patient-plans-for-a-mri-linac
#2
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/28635614/advanced-treatment-planning-using-direct-4d-optimisation-for-pencil-beam-scanned-particle-therapy
#3
Kinga Bernatowicz, Ye Zhang, Rosalind Lucy Perrin, Damien Charles Weber, Antony John Lomax
We report on development of a new four-dimensional (4D) optimisation approach for scanned proton beams, which incorporates both irregular motion patterns and the delivery dynamics of the treatment machine into the plan optimiser. Furthermore, we assess the effectiveness of this technique to reduce dose to critical structures in proximity to moving targets, while maintaining effective target dose homogeneity and coverage. The proposed approach has been tested using both a simulated phantom and a clinical liver cancer case, and allows for realistic 4D calculations and optimisation using irregular breathing patterns extracted from e...
June 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28632501/evaluation-of-automatic-dose-rate-control-for-flat-panel-imaging-using-a-spatial-frequency-domain-figure-of-merit
#4
Michiel Dehairs, Hilde Bosmans, Walter Desmet, Nicholas W Marshall
Current automatic dose rate controls (ADRCs) of dynamic x-ray imaging systems adjust acquisition parameters in response to changes in patient thickness in order to achieve a constant signal level in the image receptor. This work compares a 3 parameter (3P) ADRC control to a more flexible 5-parameter (5P) method to meet this goal. A phantom composed of 15 composite poly(methyl) methacrylate (PMMA)/aluminium (Al) plates was imaged on a Siemens Artis Q dynamic system using standard 3P and 5P ADRC technique. Phantom thickness covered a water equivalent thickness range of 2...
June 20, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28632500/photon-detection-efficiency-of-laboratory-based-x-ray-phase-contrast-imaging-techniques-for-mammography-a-monte-carlo-study
#5
Somayeh Saghamanesh, Seyed Mohammad Reza Aghamiri, Alireza Kamali-Asl, Wataru Yashiro
An important challenge in real-world biomedical applications of X-ray phase contrast imaging (XPCI) techniques is the efficient use of the photon flux generated by an incoherent and polychromatic X-ray source. This efficiency can directly influence dose and exposure time and ideally should not affect the superior contrast and sensitivity of XPCI. In this paper, we present a quantitative evaluation of the photon detection efficiency of two laboratory-based XPCI methods, grating interferometry (GI) and coded-aperture (CA)...
June 20, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28632499/model-based-sphere-localization-mbsl-in-x-ray-projections
#6
Stefan Sawall, Joscha Maier, Carsten Leinweber, David Prox, Carsten Funck, Jan Kuntz, Marc Kachelriess
The detection of spherical markers in x-ray projections is an important task in a variety of applications, e.g. geometric calibration and detector distortion correction. Therein, the projection of the sphere center on the detector is of particular interest as the used spherical beads are no ideal point-like objects. Only few methods have been proposed to estimate this respective position on the detector with sufficient accuracy and surrogate positions, e.g. the center of gravity, are used, impairing the results of subsequent algorithms...
June 20, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28604358/dual-stage-beamforming-in-absence-of-front-end-receive-focusing
#7
Deep Bera, Johan Bosch, Martin Verweij, Nico De Jong, Hendrik Vos
Ultrasound front-end receive designs for miniature, wireless, and/or matrix transducers might be simplified considerably by direct element summation in receive. In this paper we develop a dual-stage beamforming technique which is able to produce a high quality image from scanlines that are produced with focused transmit, and simple summation in receive (no delays). We call this Non-Delayed Sequential Beamforming (NDSB). In the first stage, low-resolution RF scanlines are formed by simple summation of element signals from a running sub-aperture...
June 12, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28594336/flagged-uniform-particle-splitting-for-variance-reduction-in-proton-and-carbon-ion-track-structure-simulations
#8
Jose Asuncion Ramos-Mendez, Jan Schuemann, Sebastien Incerti, Harald Paganetti, Reinhard Schulte, Bruce Faddegon
Flagged uniform particle splitting was implemented with two methods to improve computational efficiency of Monte Carlo track structure simulations with TOPAS-nBio by enhancing the production of secondary electrons in ionization events. In Method 1 the Geant4 kernel was modified. In Method 2 Geant4 was not modified. In both methods a unique flag number assigned to each new split electron was inherited by its progeny, permitting reclassification of the split events as if produced by correlated histories. Computational efficiency and accuracy were evaluated for simulations of 0...
June 8, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28594333/quantification-of-carotid-artery-plaque-stability-with-multiple-region-of-interest-based-ultrasound-strain-indices-and-relationship-with-cognition
#9
Nirvedh Meshram, Tomy Varghese, Carol Mitchell, Daren Jackson, Stephanie Wilbrand, Bruce Hermann, Robert Dempsey
Vulnerability and instability in carotid artery plaque has been assessed based on strain variations using noninvasive ultrasound imaging. We previously demonstrated that carotid plaques with higher strain indices in a region of interest (ROI) correlated to patients with lower cognition, probably due to cerebrovascular emboli arising from these unstable plaques. This work attempts to characterize the strain distribution throughout the entire plaque region instead of being restricted to a single localized ROI...
June 8, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28593931/performance-characterization-of-a-3d-liquid-scintillation-detector-for-discrete-spot-scanning-proton-beam-systems
#10
Chinmay Darne, Fahed Alsanea, Daniel Robertson, Narayan Sahoo, Sam Beddar
Existing systems for proton beam dosimetry are limited in their ability to provide a complete, accurate, and detailed account of volumetric dose distribution. In this work, we describe the design and development of a portable, fast, and reusable liquid scintillator-based three-dimensional (3D) optical detection system for use in proton therapy. Our long-term goal is to use this system clinically for beam characterization, dosimetry, and quality assurance studies of discrete spot scanning proton beam systems...
June 8, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28590941/ttc-pluronic-3d-radiochromic-gel-dosimetry-of-ionizing-radiation
#11
Marek Kozicki, Klaudia Kwiatos, Slawomir Kadlubowski, Mariusz Dudek
This work reports the first results obtained using a new 3D radiochromic gel dosimeter. The dosimeter is an aqueous physical gel matrix made of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127, PEO-PPO-PEO) doped with a representative of tetrazolium salts, 2,3,5-triphenyltetrazolium chloride (TTC). There were several reasons for the choice of Pluronic as a gel forming substrate: i) the high degree of transparency and colourlessness; ii) the possibility of gel dosimeter preparation at both high and low temperatures due to the phase behaviour of Pluronic; iii) the broad temperature range over which the TTC-Pluronic dosimeter is stable; and iv) the non-toxicity of Pluronic...
June 7, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28590940/simdosect-dose-reporting-software-based-on-monte-carlo-simulation-for-a-320-detector-row-cone-beam-ct-scanner-and-icrp-computational-adult-phantoms
#12
Maria Cros, Raoul Joemai, Jacob Koos Geleijns, Diego Molina, Marçal Salvadó
This study aims to develop and test software for assessing and reporting doses for standard patients undergoing computed tomography (CT) examinations in a 320 detector-row cone-beam scanner. The software, called SimDoseCT, is based on Monte Carlo (MC) simulation code, which was developed to calculate organ- and effective doses in ICRP anthropomorphic adult reference computational phantoms for acquisitions with the Aquilion ONE CT scanner (Toshiba). MC simulation was validated by comparing CTDI measurements within standard CT dose phantoms with results from simulation under the same conditions...
June 7, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28590938/combined-passive-acoustic-mapping-and-magnetic-resonance-thermometry-for-monitoring-phase-shift-nanoemulsion-enhanced-focused-ultrasound-therapy
#13
Calum Crake, F Can Meral, Mark Burgess, Iason Papademetriou, Nathan McDannold, Tyrone Porter
Focused ultrasound (FUS) has the potential to enable precise, image-guided noninvasive surgery for the treatment of cancer in which tumors are identified and destroyed in a single integrated procedure. However, success of the method in highly vascular organs has been limited due to heat losses to perfusion, requiring development of techniques to locally enhance energy absorption and heating. In addition, FUS procedures are conventionally monitored using MRI, which provides excellent anatomical images and can map temperature, but is not capable of capturing the full gamut of available data such as the acoustic emissions generated during this inherently acoustically-driven procedure...
June 7, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28586318/modelling-of-induced-electric-fields-based-on-incompletely-known-magnetic-fields
#14
Ilkka Laakso, Valerio De Santis, Silvano Cruciani, Tommaso Campi, Mauro Feliziani
Determining the induced electric fields in the human body is a fundamental problem in bioelectromagnetics that is important for both evaluation of safety of electromagnetic fields and medical applications. However, existing techniques for numerical modelling of induced electric fields require detailed information about the sources of the magnetic field, which may be unknown or difficult to model in realistic scenarios. Here, we show how induced electric fields can accurately be determined in the case that the magnetic fields are known only approximately, e...
June 6, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28582269/automated-diagnosis-of-prostate-cancer-in-multi-parametric-mri-based-on-multimodal-convolutional-neural-networks
#15
Minh Hung Le, Jingyu Chen, Liang Wang, Zhiwei Wang, Wenyu Liu, Kwang-Ting Tim Cheng, Xin Yang
Automated methods for prostate cancer (PCa) diagnosis in multi-parametric magnetic resonance images (MP-MRI) are critical for increasing the survival rate of patients and alleviating requirements in radiology reading and reducing risk of over-/under-treatment. This paper presents an automated method based on multimodal convolutional neural networks (CNNs) for two PCa diagnosis tasks: 1) distinguishing between cancer and noncancerous tissues, 2) distinguishing between clinically significant (CS) and indolent PCa...
June 5, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28582267/detection-of-anatomical-changes-in-lung-cancer-patients-with-2d-time-integrated-2d-time-resolved-and-3d-time-integrated-portal-dosimetry-a-simulation-study
#16
Cecile J A Wolfs, Mariana Brás, Lotte Schyns, Sebastiaan Nijsten, Wouter van Elmpt, Stefan Scheib, Christof Baltes, Mark Podesta, Frank Verhaegen
The aim of this work is to assess the performance of 2D time-integrated (2D-TI), 2D time-resolved (2D-TR) and 3D time-integrated (3D-TI) portal dosimetry in detecting dose discrepancies between the planned and (simulated) delivered dose caused by simulated changes in the anatomy of lung cancer patients. For six lung cancer patients, tumor shift, tumor regression and pleural effusion are simulated by modifying their CT images. Based on the modified CT images, time-integrated (TI) and time-resolved (TR) portal dose images (PDIs) are simulated and 3D-TI doses are calculated...
June 5, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28582266/a-beam-monitoring-and-validation-system-for-continuous-line-scanning-in-proton-therapy
#17
Grischa Klimpki, Serena Psoroulas, Christian Bula, Urs Rechsteiner, Michael Eichin, Damien Weber, Antony Lomax, David Meer
Line scanning represents a faster and potentially more flexible form of pencil beam scanning than conventional <i>step-and-shoot</i> irradiations. It seeks to minimize dead times in beam delivery whilst preserving the possibility to modulate the dose at any point in the target volume. Our second generation proton gantry features irradiations in line scanning mode, but it still lacks a dedicated monitoring and validation system that guarantees patient safety throughout beam delivery. We report on its design and implementation in this paper...
June 5, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28582265/application-of-fluence-field-modulation-to-proton-computed-tomography-for-proton-therapy-imaging
#18
Georgios Dedes, Ludovica De Angelis, Simon Rit, David Hansen, Claus Belka, Vladimir Bashkirov, Robert Johnson, George Coutrakon, Keith Schubert, Guillaume Landry, Reinhard Schulte, Katia Parodi
This simulation study presents the application of fluence field modulated computed tomography (FFMCT), initially developed for x-ray CT, to proton computed tomography (pCT). By using pencil beam (PB) scanning, fluence modulated pCT (FMpCT) may achieve variable image quality in a pCT image and imaging dose reduction. Three virtual phantoms, a uniform cylinder and two patients, were studied using Monte Carlo simulations of an ideal list-mode pCT scanner. Regions of interests (ROI) were selected for high image quality and only PBs intercepting them preserved full fluence (FF)...
June 5, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28574405/multi-institutional-microct-image-comparison-of-image-guided-small-animal-irradiators
#19
Chris Daniel Johnstone, Patricia Lindsay, Edward Graves, Eugene Wong, Jessica Perez, Yannick Poirier, Youssef Ben-Bouchta, Thilakshan Kanesalingam, Haijian Chen, Ashley Rubinstein, Ke Sheng, Magdalena Bazalova-Carter
To recommend imaging protocols and establish tolerance levels for microCT image quality assurance (QA) performed on conformal image-guided small animal irradiators. Method and Materials: A fully automated QA software SAPA (small animal phantom analyzer) for image analysis of the commercial Shelley micro-CT MCTP 610 phantom was developed, in which quantitative analyses of CT number linearity, signal-to-noise ratio (SNR), uniformity and noise, geometric accuracy, spatial resolution by means of modulation transfer function (MTF), and CT contrast were performed...
June 2, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28573978/automatic-contour-propagation-using-deformable-image-registration-to-determine-delivered-dose-to-spinal-cord-in-head-and-neck-cancer-radiotherapy
#20
Ping Lin Yeap, David Noble, Karl Harrison, Amy Bates, Neil Burnet, Rajesh Jena, Marina Romanchikova, Michael Sutcliffe, Simon Thomas, Gill Barnett, Richard Benson, Sarah Jefferies, M Parker
To determine delivered dose to the spinal cord, a technique has been developed to propagate manual contours from kilovoltage computed-tomography (kVCT) scans for treatment planning to megavoltage computed-tomography (MVCT) guidance scans. The technique uses the Elastix software to perform intensity-based deformable image registration of each kVCT scan to the associated MVCT scans. The registration transform is then applied to contours of the spinal cord drawn manually on the kVCT scan, to obtain contour positions on the MVCT scans...
June 2, 2017: Physics in Medicine and Biology
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