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Medical Physics

Martin Sjölin, Mats Danielsson
PURPOSE: Photon-counting edge-on detectors are currently being considered for use in clinical computed tomography (CT) systems. A method for geometric calibration of edge-on detectors mounted on a CT-gantry has been developed and evaluated. The method is complementary to the geometrical calibration methods developed for CT systems using flat-panel detectors and takes the extra dimension of the edge-on detectors (along the direction of the x-rays) into account. METHODS: The method uses projection images of a simple phantom together with geometrical arguments to accurately estimate the orientation and relative position of the edge-on detectors...
November 2016: Medical Physics
P Trnková, A Bolsi, F Albertini, D C Weber, A J Lomax
PURPOSE: A detailed analysis of 2728 intensity modulated proton therapy (IMPT) fields that were clinically delivered to patients between 2007 and 2013 at Paul Scherrer Institute (PSI) was performed. The aim of this study was to analyze the results of patient specific dosimetric verifications and to assess possible correlation between the quality assurance (QA) results and specific field metrics. METHODS: Dosimetric verifications were performed for every IMPT field prior to patient treatment...
November 2016: Medical Physics
Gregory Warrell, Diana Shvydka, E Ishmael Parsai
PURPOSE: A practical means of delivering both therapeutic radiation and hyperthermia to a deep-seated target has been identified in the literature as highly desirable, provided it is capable of generating sufficient temperatures over the defined target volume. The authors present continued development of a dual-modality thermobrachytherapy (TB) seed, investigating its capabilities in delivering prescribed hyperthermia to realistic deep-seated targets. METHODS: The TB seed is based on the ubiquitous low dose-rate (LDR) brachytherapy permanent implant...
November 2016: Medical Physics
Huiqiao Xie, Weixing Cai, Lily Yang, Hui Mao, Xiangyang Tang
PURPOSE: Differential phase contrast CT has been recognized as an x-ray imaging method with the potential to greatly improve the differentiation of soft tissues. Talbot interferometry has been one of the promising solutions allowing implementation with commercially available x-ray tubes with a polychromatic spectrum. Mainly due to imperfections in grating fabrication and the polychromatic spectrum of x-ray beam, a twin-peaks phenomenon may exist in phase stepping curves (PSCs) and degrade the performance of phase retrieval...
November 2016: Medical Physics
Arash Darafsheh, Reza Taleei, Alireza Kassaee, Jarod C Finlay
PURPOSE: Proton beam dosimetry using bare plastic optical fibers has emerged as a simple approach to proton beam dosimetry. The source of the signal in this method has been attributed to Čerenkov radiation. The aim of this work was a phenomenological study of the nature of the visible light responsible for the signal in bare fiber optic dosimetry of proton therapy beams. METHODS: Plastic fiber optic probes embedded in solid water phantoms were irradiated with proton beams of energies 100, 180, and 225 MeV produced by a proton therapy cyclotron...
November 2016: Medical Physics
R Al Darwish, A H Staudacher, Y Li, M P Brown, E Bezak
PURPOSE: In targeted radionuclide therapy, regional tumors are targeted with radionuclides delivering therapeutic radiation doses. Targeted alpha therapy (TAT) is of particular interest due to its ability to deliver alpha particles of high linear energy transfer within the confines of the tumor. However, there is a lack of data related to alpha particle distribution in TAT. These data are required to more accurately estimate the absorbed dose on a cellular level. As a result, there is a need for a dosimeter that can estimate, or better yet determine the absorbed dose deposited by alpha particles in cells...
November 2016: Medical Physics
Chin-Hui Wu, Yi-Jen Liao, Tzung-Yi Lin, Yu-Cheng Chen, Shung-Shung Sun, Yen-Wan Hsueh Liu, Shih-Ming Hsu
PURPOSE: Primary hepatocellular carcinoma and metastatic liver tumors are highly malignant tumors in Asia. The incidence of fatal liver cancer is also increasing in the United States. The aim of this study was to establish a spherical tumor model and determine its accuracy in predicting the absorbed dose in yttrium-90 (Y-90) microsphere therapy for liver cancer. METHODS: Liver morphology can be approximated by a spherical model comprising three concentric regions representing necrotic, tumor, and normal liver tissues...
November 2016: Medical Physics
Zhou Li, Guanhua Deng, Zhe Li, Sherman Xuegang Xin, Song Duan, Maoying Lan, Sa Zhang, Yixin Gao, Jun He, Songtao Zhang, Hongming Tang, Weiwei Wang, Shuai Han, Qing X Yang, Ling Zhuang, Jiani Hu, Feng Liu
PURPOSE: Knowledge of dielectric properties of malignant human tissues is necessary for the recently developed magnetic resonance (MR) technique called MR electrical property tomography. This technique may be used in early tumor detection based on the obvious differentiation of the dielectric properties between normal and malignant tissues. However, the dielectric properties of malignant human tissues in the scale of the Larmor frequencies are not completely available in the literature...
November 2016: Medical Physics
Kartik Jain, Jingfeng Jiang, Charles Strother, Kent-André Mardal
PURPOSE: Blood flow in intracranial aneurysms has, until recently, been considered to be disturbed but still laminar. Recent high resolution computational studies have demonstrated, in some situations, however, that the flow may exhibit high frequency fluctuations that resemble weakly turbulent or transitional flow. Due to numerous assumptions required for simplification in computational fluid dynamics (CFD) studies, the occurrence of these events, in vivo, remains unsettled. The detection of these fluctuations in aneurysmal blood flow, i...
November 2016: Medical Physics
Christiane S Burton, John R Mayo, Ian A Cunningham
PURPOSE: X-ray digital subtraction angiography (DSA) is widely used for vascular imaging. However, motion artifacts render it largely unsuccessful for some applications including cardiac imaging. Dual-energy imaging using fast kV switching was proposed in the past to provide the benefits of DSA with fewer motion artifacts, but image quality was inferior to DSA. This study compares the iodine Rose SNR that can be achieved using dual-energy methods, called energy-subtraction angiography (ESA), with that of DSA and examines the technical conditions required to achieve near-optimal SNR...
November 2016: Medical Physics
Mariska de Smet, Danny Schuring, Sebastiaan Nijsten, Frank Verhaegen
PURPOSE: To develop a clinically feasible method for dose calculations on cone beam CT (CBCT) images of two different vendors, and to determine the accuracy of these dose calculations for lung cancer patients. METHODS: Lung cancer patients with CBCT imaging (n = 10 for Elekta, n = 6 for Varian) and a repeated planning CT scan on the same day were selected. For CBCT dose calculations, an adapted Hounsfield units-to-mass density table (HU table) was used which was obtained by comparing CT values of corresponding points on the CBCT and the repeated planning CT scan...
November 2016: Medical Physics
Alejandro Garcia-Romero, Araceli Hernandez-Vitoria, Esther Millan-Cebrian, Veronica Alba-Escorihuela, Sonia Serrano-Zabaleta, Pablo Ortega-Pardina
PURPOSE: The aim of this work is to search for new metrics that could give more reliable acceptance/rejection criteria on the IMRT verification process and to offer solutions to the discrepancies found among different conventional metrics. Therefore, besides conventional metrics, new ones are proposed and evaluated with new tools to find correlations among them. These new metrics are based on the processing of the dose-volume histogram information, evaluating the absorbed dose differences, the dose constraint fulfillment, or modified biomathematical treatment outcome models such as tumor control probability (TCP) and normal tissue complication probability (NTCP)...
November 2016: Medical Physics
J T Taylor, G Poludniowski, T Price, C Waltham, P P Allport, G L Casse, M Esposito, P M Evans, S Green, S Manger, S Manolopoulos, J Nieto-Camero, D J Parker, J Symons, N M Allinson
PURPOSE: Radiography and tomography using proton beams promise benefit to image guidance and treatment planning for proton therapy. A novel proton tracking detector is described and experimental demonstrations at a therapy facility are reported. A new type of proton CT reconstructing relative "scattering power" rather than "stopping power" is also demonstrated. Notably, this new type of imaging does not require the measurement of the residual energies of the protons. METHODS: A large area, silicon microstrip tracker with high spatial and temporal resolution has been developed by the Proton Radiotherapy Verification and Dosimetry Applications consortium and commissioned using beams of protons at iThemba LABS, Medical Radiation Department, South Africa...
November 2016: Medical Physics
Hugo Palmans, Stanislav M Vatnitsky
PURPOSE: To propose a formalism for the reference dosimetry of scanned light-ion beams consistent with IAEA TRS-398 and Alfonso et al. [Med. Phys. 35, 5179-5186 (2008)]. To identify machine-specific reference (msr) fields and plan-class specific reference (pcsr) fields consistent with the definitions given by Alfonso et al. To review the literature of beam monitor calibration in scanned beams using three different methods in terms of this common formalism. METHODS: Four types of msr fields are identified as those that are meant to calibrate the beam monitor for scanned beams with particular energies...
November 2016: Medical Physics
Lei Zhu
PURPOSE: Excessive scatter contamination fundamentally limits the image quality of cone-beam CT (CBCT), hindering its quantitative use in clinical applications. The author has previously proposed an effective scatter correction method for CBCT using primary modulation. A Fourier transform-based algorithm (FTPM) was implemented to estimate scatter from modulated projections, with a few limitations including the assumption of uniform modulation frequency and magnitude that becomes less accurate in the presence of beam-hardening and other nonideal effects...
November 2016: Medical Physics
Klaus Bratengeier, Kostyantyn Holubyev
PURPOSE: To suggest a definition of dose deposition anisotropy for the purpose of ad hoc adaptation of intensity modulated arc therapy (IMRT) and volumetric arc therapy (VMAT), particularly in the vicinity of important organs at risk (OAR), also for large deformations. METHODS: Beam's-eye-view (BEV) based fluence warping is a standard adaptation method with disadvantages for strongly varying OAR shapes. 2-Step-adaptation overcomes these difficulties by a deeper analysis of the 3D properties of adaptation processes, but requires separate arcs for every OAR to spare, which makes it impractical for cases with multiple OARs...
November 2016: Medical Physics
Scott D Wollenweber, Brad J Kemp
PURPOSE: This investigation aimed to develop a scanner quantification performance methodology and compare multiple metrics between two scanners under different imaging conditions. Most PET scanners are designed to work over a wide dynamic range of patient imaging conditions. Clinical constraints, however, often impact the realization of the entitlement performance for a particular scanner design. Using less injected dose and imaging for a shorter time are often key considerations, all while maintaining "acceptable" image quality and quantitative capability...
November 2016: Medical Physics
Aimilia Gastounioti, Andrew Oustimov, Brad M Keller, Lauren Pantalone, Meng-Kang Hsieh, Emily F Conant, Despina Kontos
PURPOSE: With raw digital mammograms (DMs), which retain the relationship with x-ray attenuation of the breast tissue, not being routinely available, processed DMs are often the only viable means to acquire imaging measures. The authors investigate differences in quantitative measures of breast density and parenchymal texture, shown to have value in breast cancer risk assessment, between the two DM representations. METHODS: The authors report data from 8458 pairs of bilateral raw ("FOR PROCESSING") and processed ("FOR PRESENTATION") DMs acquired from 4278 women undergoing routine screening evaluation, collected with DM units from two different vendors...
November 2016: Medical Physics
Min-Young Lee, Bin Han, Cesare Jenkins, Lei Xing, Tae-Suk Suh
PURPOSE: The purpose of total body irradiation (TBI) techniques is to deliver a uniform radiation dose to the entire volume of a patient's body. Due to variations in the thickness of the patient, it is difficult to produce such a uniform dose distribution throughout the body. In many techniques, a compensator is used to adjust the dose delivered to various sections of the patient. The current study aims to develop and validate an innovative method of using depth-sensing cameras and 3D printing techniques for TBI treatment planning and compensator fabrication...
November 2016: Medical Physics
Hossein Arabi, Habib Zaidi
PURPOSE: The authors evaluate the performance of shape-based averaging (SBA) technique for whole-body bone segmentation from MRI in the context of MRI-guided attenuation correction (MRAC) in hybrid PET/MRI. To enhance the performance of the SBA scheme, the authors propose to combine it with statistical atlas fusion techniques. Moreover, a fast and efficient shape comparison-based atlas selection scheme was developed and incorporated into the SBA method. METHODS: Clinical studies consisting of PET/CT and MR images of 21 patients were used to assess the performance of the SBA method...
November 2016: Medical Physics
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