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Medical Physics

François Michaud, Ning Li, Rosalie Plantefève, Zeynab Nosrati, Charles Tremblay, Katayoun Saatchi, Gerald Moran, Alexandre Bigot, Urs O Häfeli, Samuel Kadoury, An Tang, Pierre Perreault, Sylvain Martel, Gilles Soulez
PURPOSE: To demonstrate the feasibility of using a custom gradient sequence on an unmodified 3T magnetic resonance imaging (MRI) scanner to perform magnetic resonance navigation (MRN) by investigating the blood flow control method in vivo, reproducing the obtained rheology in a phantom mimicking porcine hepatic arterial anatomy, injecting magnetized microbead aggregates through an implantable catheter, and steering the aggregates across arterial bifurcations for selective tumor embolization...
November 19, 2018: Medical Physics
Kuo Men, Huaizhi Geng, Chingyun Cheng, Haoyu Zhong, Mi Huang, Yong Fan, John P Plastaras, Alexander Lin, Ying Xiao
PURPOSE: Manual delineation of organs-at-risk (OARs) in radiotherapy is both time-consuming and subjective. Automated and more accurate segmentation is of the utmost importance in clinical application. The purpose of this study is to further improve the segmentation accuracy and efficiency with a novel network named Convolutional Neural Networks (CNN) Cascades. METHODS: CNN Cascades was a two-step, coarse-to-fine approach that consisted of a Simple Region Detector (SRD) and a Fine Segmentation Unit (FSU)...
November 19, 2018: Medical Physics
Pasquale Tamborra, Erica Martinucci, Raffaella Massafra, Marco Bettiol, Caterina Capomolla, Annarita Zagari, Vittorio Didonna
INTRODUCTION: Before the approval of any IMRT or VMAT treatment plan, QA tests are needed to reveal potential errors such as an inaccurate calculation of the dose distribution, the failure of the record-and-verify system or the delivery system of the linear accelerator. Currently the method adopted to compare the measured dose distribution with the TPS calculated dose distribution is gamma analysis. However gamma analysis has been shown to be ineffective for the clinical evaluation of treatment plans...
November 19, 2018: Medical Physics
Eunhee Kang, Hyun Jung Koo, Dong Hyun Yang, Joon Bum Seo, Jong Chul Ye
PURPOSE: In multiphase coronary CT angiography (CTA), a series of CT images are taken at different levels of radiation dose during the examination. Although this reduces the total radiation dose, the image quality during the low-dose phases is significantly degraded. Recently, deep neural network approaches based on supervised learning technique have demonstrated impressive performance improvement over conventional model-based iterative methods for low-dose CT. However, matched low- and routine- dose CT image pairs are difficult to obtain in multiphase CT...
November 17, 2018: Medical Physics
Vimal K Desai, Zacariah E Labby, Megan A Hyun, Larry A DeWerd, Wesley S Culberson
PURPOSE: The determination of absorbed dose to water from external beam radiotherapy using radiation detectors is currently rooted in calibration protocols that do not account for modulations encountered in patient-specific deliveries. Detector response in composite clinical fields has not been extensively studied due to the time and effort required to determine these corrections on a case-by-case basis. To help bridge this gap in knowledge, corrections for the Exradin A1SL scanning chamber were determined in a large number of composite clinical fields using Monte Carlo methods...
November 17, 2018: Medical Physics
Eric Knull, Aytekin Oto, Scott Eggener, David Tessier, Serkan Guneyli, Aritrick Chatterjee, Aaron Fenster
PURPOSE: Prostate cancer is the most common non-cutaneous cancer among men in the USA.[1] Focal laser thermal ablation (FLA) has the potential to control small tumours while preserving urinary and erectile function by leaving the neurovascular bundles and urethral sphincters intact. Accurate needle guidance is critical to the success of FLA. Multi-parametric magnetic resonance images (mpMRI) can be used to identify targets, guide needles, and assess treatment outcomes. In this study, we evaluated the location of ablation zones relative to targeted lesions in 23 patients who underwent FLA therapy in a phase II trial...
November 17, 2018: Medical Physics
Huang Lin, Ge Shaoli, Zheng Zhu, Jiang Huabei
PURPOSE: Conventional antenna used in thermoacoustic imaging (TAI) is often bulky, making it difficult to translate TAI from the bench to the clinic. In this paper, we proposed a handheld dipole antenna which will be a good candidate for the construction of a compact TAI system. METHODS: Here, we propose a TAI system based on a handheld dipole antenna with an aperture of 6 cm and a weight of 230 g. Compensation of the electric field attenuation for such a system was also investigated...
November 16, 2018: Medical Physics
C Lindsay, M Bazalova-Carter, A Wang, D Shedlock, M Wu, M Newson, L Xing, W Ansbacher, R Fahrig, J Star-Lack
PURPOSE: Combined kV-MV CBCT imaging has been proposed for two potentially important image-guided radiotherapy applications: 1) scan time reduction (STR) and 2) metal artifact reduction (MAR). However, the feasibility of these techniques has been in question due to the low detective quantum efficiencies (DQEs) of commercially available electronic portal imagers (EPIDs). The goal of the work was to test whether a prototype high DQE MV detector can be used to generate acceptable quality pre-treatment CBCT images at acceptable dose levels...
November 14, 2018: Medical Physics
Shuangyue Zhang, Dong Han, Jeffrey F Williamson, Tianyu Zhao, David G Politte, Bruce R Whiting, Joseph A O'Sullivan
PURPOSE: To experimentally commission a dual-energy CT (DECT) joint statistical image reconstruction (JSIR) method, which is built on a linear basis vector model (BVM) of material characterization, for proton stopping power ratio (SPR) estimation. METHODS: The JSIR-BVM method builds on the relationship between the energy-dependent photon attenuation coefficients and the proton stopping power via a pair of BVM component weights. The two BVM component images are simultaneously reconstructed from the acquired DECT sinograms and then used to predict the electron density and mean excitation energy (I-value), which are required by the Bethe equation for SPR computation...
November 13, 2018: Medical Physics
Guoqing Wu, Zhifeng Shi, Yinsheng Chen, Yuanyuan Wang, Jinhua Yu, Xiaofei Lv, Liang Chen, Xue Ju, Zhongping Chen
PURPOSE: Accurately predicting outcome (i.e., overall survival (OS) time) for higher grade glioma (HGG) has great clinical value and would provide optimized guidelines for treatment planning. Radiomics focuses on revealing underlying pathophysiological information in biomedical images for disease analysis and demonstrates promising prognostic clinical performance. In this paper, we propose a novel sparse representation-based radiomics framework to predict if HGG patients would have long or short OS time...
November 12, 2018: Medical Physics
Konstantinos P Chatzipapas, Panagiotis Papadimitroulas, Mohammad Obeidat, Kristen A McConnell, Neil Kirby, George Loudos, Niko Papanikolaou, George C Kagadis
PURPOSE: This study aims to standardize the simulation procedure in measuring DNA Double Strand Breaks (DSBs), by using advanced Monte Carlo toolkits, and newly introduced experimental methods for DNA DSB measurement. METHODS: For the experimental quantification of DNA DSB, an innovative DNA dosimeter was used to produce experimental data. GATE in combination with Geant4-DNA toolkit were exploited to simulate the experimental environment. The PDB4DNA example, of Geant4-DNA was upgraded and investigated...
November 12, 2018: Medical Physics
Kenneth J Nichols, Frank P DiFilippo, Christopher J Palestro
PURPOSE: Routine quarterly quality assurance (QA) assessment of single photon emission computed tomography (SPECT) systems includes analysis of multipurpose phantoms containing spheres and rods of various sizes. When evaluated by accreditation agencies, criteria applied to assess image quality are largely subjective. Determining a quantified image characteristic metric that emulates human reader impressions of image quality could be quite useful. Our investigation was conducted to ascertain whether image texture analysis metrics, such as those applied to PET scans to detect neoplasms, could prove helpful in linking qualitative statements of phantom sphere and rod visibility to quantified parameters...
November 12, 2018: Medical Physics
P Khobragade, Franco Rupcich, Jiahua Fan, Dominic J Crotty, Naveen M Kulkarni, Stacy D O'Connor, W Dennis Foley, Taly Gilat Schmidt
PURPOSE: Identifying an appropriate tube current setting can be challenging when using iterative reconstruction due to the varying relationship between spatial resolution, contrast, noise, and dose across different algorithms. This study developed and investigated the application of a generalized detectability index (d'gen) to determine the noise parameter to input to existing AEC systems to provide consistent image quality across different reconstruction approaches. METHODS: This study proposes a task-based automated exposure control (AEC) method using a generalized detectability index (d'gen)...
November 12, 2018: Medical Physics
Christopher Daniel Johnstone, Francois Therriault-Proulx, Luc Beaulieu, Magdalena Bazalova-Carter
PURPOSE: To characterize a small plastic scintillator developed for high resolution, real-time dosimetry of therapy and imaging x-ray beams delivered by an image-guided small animal irradiator. MATERIALS AND METHODS: A 1 mm diameter, 1 mm long polystyrene BCF-60 scintillating fiber dosimeter was characterized with 220 kVp therapy and 40, 50, 60, 70, and 80 kVp imaging beams on the Small Animal Research Platform (SARRP). Scintillator output, sensitivity (charge per unit dose), linearity, and 0...
November 12, 2018: Medical Physics
Robin De Roover, Wouter Crijns, Kenneth Poels, Steven Michiels, An Nulens, Bianca Vanstraelen, Saskia Petillion, Marisol De Brabandere, Karin Haustermans, Tom Depuydt
PURPOSE: A fast-rotating O-ring dedicated IMRT/VMAT delivery system, the Halcyon, is delivered by default with a fully pre-configured photon beam model in the TPS. This work reports on the validation and achieved IMRT/VMAT delivery quality on the system. METHODS: Acceptance testing followed the vendor's installation product acceptance and was supplemented with mechanical QA. The dosimetric calibration was performed according to the IAEA TRS-398 code of practice, delivering 600 cGy/min at 10 cm depth, a 90 cm source-surface distance and a 10x10 cm² field size...
November 11, 2018: Medical Physics
Satyapal Rathee, B Gino Fallone, Stephen Steciw
PURPOSE: Electronic portal imaging devices (EPIDs) are potentially useful for dosimetric verification in integrated MRI-linac systems. This work presents the reproducibility, linearity image lag, and radiation field profiles in a conventional EPID, with and without a 0.5 T parallel magnetic field present in a 6MV photon beam. METHODS: An aS500 EPID was modified to function in strong magnetic fields. All measurements were made using the linac-MR installed at the Cross Cancer Institute...
November 11, 2018: Medical Physics
Alfred M Franz, Alexander Seitel, Dominique Cheray, Lena Maier-Hein
PURPOSE: Electromagnetic (EM) tracking is a key technology in image-guided therapy. A new EM Micro Sensor was presented by Polhemus Inc.; it is the first to enable localization of medical instruments through their trackers. Different field generators (FGs) are available by Polhemus, one being almost as small as a sugar cube. As accuracy and robustness of tracking are known challenges to using EM trackers in clinical environments, the goal of this study was a standardized assessment of the Micro Sensor in both a laboratory (lab) and a computed tomography (CT) environment METHODS: The Micro Sensor was assessed by means of Hummel et al...
November 10, 2018: Medical Physics
Gregory J Anthony, Kenneth B Bader, James Wang, Marta Zamora, Allison Ostdiek, Tatjana Antic, Sascha Kruger, Steffen Weiss, William C Trogler, Sarah L Blair, Andrew C Kummel, Steffen Sammet
PURPOSE: In this study, the efficacy of transurethral insonation of silica-shell ultrasound-triggered phase-shift emulsions (sUPEs) doped with MR contrast was evaluated. The influence of sUPEs on MR imaging assessment of the ablation zone was also investigated. METHODS: sUPEs were doped with a magnetic resonance (MR) contrast agent, Gd2 O3 , to assess ultrasound transition. Injections of saline (sham), saline and sUPEs alone, and saline and sUPEs with Optison microbubbles were performed under guidance of a prototype interventional MRI navigation platform in a healthy canine prostate...
November 10, 2018: Medical Physics
Guang Li, Shouhua Luo, Chenyu You, Matthew Getzin, Liang Zheng, Ge Wang, Ning Gu
PURPOSE: Cone-beam (CB) CT is a powerful non-invasive imaging modality, and is widely used in many applications. Accurate geometric parameters are essential for high-quality image reconstruction. Usually, a CBCT system with higher spatial resolution, particularly on the order of microns or nanometers, will be more sensitive to the parametric accuracy. Here we propose a novel calibration method combining a simple phantom containing ball bearing markers and an advanced optimization procedure...
November 10, 2018: Medical Physics
Ana Lourenço, Hugo Bouchard, Sebastian Galer, Gary Royle, Hugo Palmans
PURPOSE: In all recent protocols for the reference dosimetry of clinical proton beams ionization chamber perturbation factors are assumed to be unity. In this work, such factors were computed using the FLUKA Monte Carlo code for three ionization chamber types, with particular attention to the influence of nuclear interactions. METHODS: The accuracy of the transport algorithms implemented in FLUKA was first evaluated by performing a Fano cavity test. Ionization chamber perturbation factors were computed for the PTW-34001 Roos® and the PTW-34070 and PTW-34073 Bragg peak® chambers for proton beams of 60 to 250 MeV using the same transport parameters that were needed to pass the Fano test...
November 10, 2018: Medical Physics
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