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Medical Physics

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September 2016: Medical Physics
Michael Krämer, Emanuele Scifoni, Marco Durante
No abstract text is available yet for this article.
September 2016: Medical Physics
Eduardo Galiano
No abstract text is available yet for this article.
September 2016: Medical Physics
Eenas A Omari, Beth Erickson, Christopher Ehlers, Francisco Quiroz, George Noid, David T Cooper, Martin Lachaine, X Allen Li
PURPOSE: Substantial intrafraction organ motion during radiation therapy (RT) for pancreatic cancer is well recognized as a major limiting factor for accurate delivery of RT. The aim of this work is to determine the feasibility of monitoring the intrafractional motion of the pancreas or surrounding structures using ultrasound for RT delivery. METHODS: Transabdominal ultrasound (TAUS) and 4DCT data were acquired on ten pancreatic cancer patients during radiation therapy process in a prospective study...
September 2016: Medical Physics
P Guiral, J Ribouton, P Jalade, R Wang, J-M Galvan, G-N Lu, P Pittet, A Rivoire, L Gindraux
PURPOSE: High dose rate brachytherapy (HDR-BT) is widely used to treat gynecologic, anal, prostate, head, neck, and breast cancers. These treatments are typically administered in large dose per fraction (>5 Gy) and with high-gradient-dose-distributions, with serious consequences in case of a treatment delivery error (e.g., on dwell position and dwell time). Thus, quality assurance (QA) or quality control (QC) should be systematically and independently implemented. This paper describes the design and testing of a phantom and an instrumented gynecological applicator for pretreatment QA and in vivo QC, respectively...
September 2016: Medical Physics
Chung Chan, Hui Liu, Yariv Grobshtein, Mitchel R Stacy, Albert J Sinusas, Chi Liu
PURPOSE: Partial volume correction (PVC) methods typically improve quantification at the expense of increased image noise and reduced reproducibility. In this study, the authors developed a novel voxel-based PVC method that incorporates anatomical knowledge to improve quantification while suppressing noise for cardiac SPECT/CT imaging. METHODS: In the proposed method, the SPECT images were first reconstructed using anatomical-based maximum a posteriori (AMAP) with Bowsher's prior to penalize noise while preserving boundaries...
September 2016: Medical Physics
Kevin C Jones, François Vander Stappen, Chandra M Sehgal, Stephen Avery
PURPOSE: Measurement of the arrival times of thermoacoustic waves induced by pulsed proton dose depositions (protoacoustics) may provide a proton range verification method. The goal of this study is to characterize the required dose and protoacoustic proton range (distance) verification accuracy in a homogeneous water medium at a hospital-based clinical cyclotron. METHODS: Gaussian-like proton pulses with 17 μs widths and instantaneous currents of 480 nA (5.6 × 10(7) protons/pulse, 3...
September 2016: Medical Physics
Marco Marinelli, G Prestopino, C Verona, G Verona-Rinati
PURPOSE: Small field output correction factors have been studied by several research groups for the PTW 60019 microDiamond (MD) dosimeter, by comparing the response of such a device with both reference dosimeters and Monte Carlo simulations. A general good agreement is observed for field sizes down to about 1 cm. However, evident inconsistencies can be noticed when comparing some experimental results and Monte Carlo simulations obtained for smaller irradiation fields. This issue was tentatively attributed by some authors to unintentional large variations of the MD active surface area...
September 2016: Medical Physics
Gloria Vilches-Freixas, Jean Michel Létang, Sébastien Brousmiche, Edward Romero, Marc Vila Oliva, Daniel Kellner, Heinz Deutschmann, Peter Keuschnigg, Philipp Steininger, Simon Rit
PURPOSE: The aim of this work is to propose a general and simple procedure for the calibration and validation of kilo-voltage cone-beam CT (kV CBCT) models against experimental data. METHODS: The calibration and validation of the CT model is a two-step procedure: the source model then the detector model. The source is described by the direction dependent photon energy spectrum at each voltage while the detector is described by the pixel intensity value as a function of the direction and the energy of incident photons...
September 2016: Medical Physics
Yukinori Matsuo, Mitsuhiro Nakamura, Takashi Mizowaki, Masahiro Hiraoka
PURPOSE: The purpose of this technical note is to introduce variance component analysis to the estimation of systematic and random components in setup error of radiotherapy. METHODS: Balanced data according to the one-factor random effect model were assumed. RESULTS: Analysis-of-variance (anova)-based computation was applied to estimate the values and their confidence intervals (CIs) for systematic and random errors and the population mean of setup errors...
September 2016: Medical Physics
G P Liney, B Dong, J Begg, P Vial, K Zhang, F Lee, A Walker, R Rai, T Causer, S J Alnaghy, B M Oborn, L Holloway, P Metcalfe, M Barton, S Crozier, P Keall
PURPOSE: The pursuit of real-time image guided radiotherapy using optimal tissue contrast has seen the development of several hybrid magnetic resonance imaging (MRI)-treatment systems, high field and low field, and inline and perpendicular configurations. As part of a new MRI-linac program, an MRI scanner was integrated with a linear accelerator to enable investigations of a coupled inline MRI-linac system. This work describes results from a prototype experimental system to demonstrate the feasibility of a high field inline MR-linac...
September 2016: Medical Physics
Olga Gopan, Jing Zeng, Avrey Novak, Matthew Nyflot, Eric Ford
PURPOSE: The pretreatment physics plan review is a standard tool for ensuring treatment quality. Studies have shown that the majority of errors in radiation oncology originate in treatment planning, which underscores the importance of the pretreatment physics plan review. This quality assurance measure is fundamentally important and central to the safety of patients and the quality of care that they receive. However, little is known about its effectiveness. The purpose of this study was to analyze reported incidents to quantify the effectiveness of the pretreatment physics plan review with the goal of improving it...
September 2016: Medical Physics
Urvi Vyas, Pejman Ghanouni, Casey H Halpern, Jeff Elias, Kim Butts Pauly
PURPOSE: In transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) treatments, the acoustic and spatial heterogeneity of the skull cause reflection, absorption, and scattering of the acoustic beams. These effects depend on skull-specific parameters and can lead to patient-specific thermal responses to the same transducer power. In this work, the authors develop a simulation tool to help predict these different experimental responses using 3D heterogeneous tissue models based on the subject CT images...
September 2016: Medical Physics
Alexandra E Bourque, Stéphane Bedwani, Édith Filion, Jean-François Carrier
PURPOSE: This study introduces a novel autocontouring algorithm based on particle filter for lung tumors. It is validated on dynamic magnetic resonance (MR) images and is developed in the context of MR-linac treatments. METHODS: A sequential Monte Carlo method called particle filter is used as the main structure of the algorithm and is combined with Otsu's thresholding technique to contour lung tumors on dynamic MR images. Four non-small cell lung cancer (NSCLC) patients were imaged with a 1...
September 2016: Medical Physics
Paolo Zaffino, Patrik Raudaschl, Karl Fritscher, Gregory C Sharp, Maria Francesca Spadea
PURPOSE: Multiatlas based segmentation is largely used in many clinical and research applications. Due to its good performances, it has recently been included in some commercial platforms for radiotherapy planning and surgery guidance. Anyway, to date, a software with no restrictions about the anatomical district and image modality is still missing. In this paper we introduce plastimatch mabs, an open source software that can be used with any image modality for automatic segmentation...
September 2016: Medical Physics
Deni Hardiansyah, Wei Guo, Peter Kletting, Felix M Mottaghy, Gerhard Glatting
PURPOSE: The aim of this study was to investigate the accuracy of PET-based treatment planning for predicting the time-integrated activity coefficients (TIACs). METHODS: The parameters of a physiologically based pharmacokinetic (PBPK) model were fitted to the biokinetic data of 15 patients to derive assumed true parameters and were used to construct true mathematical patient phantoms (MPPs). Biokinetics of 150 MBq (68)Ga-DOTATATE-PET was simulated with different noise levels [fractional standard deviation (FSD) 10%, 1%, 0...
September 2016: Medical Physics
V K Rana, S Rudin, D R Bednarek
PURPOSE: Neurovascular interventional procedures using biplane fluoroscopic imaging systems can lead to increased risk of radiation-induced skin injuries. The authors developed a biplane dose tracking system (Biplane-DTS) to calculate the cumulative skin dose distribution from the frontal and lateral x-ray tubes and display it in real-time as a color-coded map on a 3D graphic of the patient for immediate feedback to the physician. The agreement of the calculated values with the dose measured on phantoms was evaluated...
September 2016: Medical Physics
Jessie Y Huang, David S Followill, Rebecca M Howell, Xinming Liu, Dragan Mirkovic, Francesco C Stingo, Stephen F Kry
PURPOSE: Dose calculation errors near metal implants are caused by limitations of the dose calculation algorithm in modeling tissue/metal interface effects as well as density assignment errors caused by imaging artifacts. The purpose of this study was to investigate two strategies for reducing dose calculation errors near metal implants: implementation of metal-based energy deposition kernels in the convolution/superposition (C/S) dose calculation method and use of metal artifact reduction methods for computed tomography (CT) imaging...
September 2016: Medical Physics
Elena Salvagnini, Hilde Bosmans, Chantal Van Ongeval, Andreas Van Steen, Koen Michielsen, Lesley Cockmartin, Lara Struelens, Nicholas W Marshall
PURPOSE: The aim of this work was twofold: (1) to examine whether, with standard automatic exposure control (AEC) settings that maintain pixel values in the detector constant, lesion detectability in clinical images decreases as a function of breast thickness and (2) to verify whether a new AEC setup can increase lesion detectability at larger breast thicknesses. METHODS: Screening patient images, acquired on two identical digital mammography systems, were collected over a period of 2 yr...
September 2016: Medical Physics
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