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Zeitschrift Für Medizinische Physik

Andreas Rinscheid, Jeesoo Lee, Peter Kletting, Ambros J Beer, Gerhard Glatting
AIM: For dosimetry in radioligand therapy, the time-integrated activity coefficients (TIACs) for organs at risk and for tumour lesions have to be determined. The used sampling scheme affects the TIACs and therefore the calculated absorbed doses. The aim of this work was to develop a general and flexible method, which analyses numerous clinically applicable sampling schedules using true time-activity curves (TACs) of virtual patients. METHOD: Nine virtual patients with true TACs of the tumours were created using a physiologically-based pharmacokinetic (PBPK) model and individual biokinetic data of five patients with neuroendocrine tumours and four with meningioma...
January 2, 2019: Zeitschrift Für Medizinische Physik
Nina Jacobsen, Andreas Deistung, Dagmar Timmann, Sophia L Goericke, Jürgen R Reichenbach, Daniel Güllmar
INTRODUCTION: Convolutional neural networks have begun to surpass classical statistical- and atlas based machine learning techniques in medical image segmentation in recent years, proving to be superior in performance and speed. However, a major challenge that the community faces are mismatch between variability within training and evaluation datasets and therefore a dependency on proper data pre-processing. Intensity normalization is a widely applied technique for reducing the variance of the data for which there are several methods available ranging from uniformity transformation to histogram equalization...
December 19, 2018: Zeitschrift Für Medizinische Physik
Gunnar Brix, Jürgen Griebel, Renate Czarwinski
The increasing frequency and complexity of medical radiation exposures to humans inevitably result in higher risks of harmful unintended or accidental radiation exposures. To ensure a high level of protection and its continuous improvement, the Directive 2013/59/Euratom thus requires to systematically record and analyze both events and near-miss events as well as, in the case of their significance, to disseminate information regarding lessons learned from these events promptly and nationwide to improve radiation protection in medicine...
December 15, 2018: Zeitschrift Für Medizinische Physik
Alexander Selvikvåg Lundervold, Arvid Lundervold
What has happened in machine learning lately, and what does it mean for the future of medical image analysis? Machine learning has witnessed a tremendous amount of attention over the last few years. The current boom started around 2009 when so-called deep artificial neural networks began outperforming other established models on a number of important benchmarks. Deep neural networks are now the state-of-the-art machine learning models across a variety of areas, from image analysis to natural language processing, and widely deployed in academia and industry...
December 12, 2018: Zeitschrift Für Medizinische Physik
Gregor Bruggmoser, Rainer Saum, Rafael Kranzer
This addendum provides correction factors for the recombination and the polarity effect for the new ionization chamber PTW PinPoint (type 31023). The measurements were made in filtered (WFF) and unfiltered (FFF) high-energy photon beams. It could be confirmed that both the initial and the general recombination effect of the chamber mainly depends on dose per pulse at the point of measurement and is independent of the filtration of the photon beam.
December 5, 2018: Zeitschrift Für Medizinische Physik
Alina Nickel, David Milford, Manuel Fischer, Martin Bendszus, Sabine Heiland
INTRODUCTION: Glioblastoma multiforme is the most frequent innate brain tumor and still yields an unfavorable prognosis of 15 months of survival after diagnosis. Animal models play an important role in the investigation of therapeutic strategies of brain tumors. Thereby, MRI is substantial to individual follow-up examination for therapeutic response. Contrast agent dosage at 1.5 and 3T MRI has been thoroughly tested, while there is hardly any data for 9.4T. Therefore, the aim of this study was to find the optimal contrast agent dosage at 9...
November 20, 2018: Zeitschrift Für Medizinische Physik
Daniela Thorwarth
No abstract text is available yet for this article.
November 15, 2018: Zeitschrift Für Medizinische Physik
K Niepel, F Kamp, C Kurz, D Hansen, S Rit, S Neppl, J Hofmaier, D Bondesson, C Thieke, J Dinkel, C Belka, K Parodi, G Landry
Inter-fractional variations of breathing pattern and patient anatomy introduce dose uncertainties in proton therapy. One approach to monitor these variations is to utilize the cone-beam computed tomography (CT, CBCT) scans routinely taken for patient positioning, reconstruct them as 4DCBCTs, and generate 'virtual CTs' (vCTs), combining the accurate CT numbers of the diagnostic 4DCT and the geometry of the daily 4DCBCT by using deformable image registration (DIR). In this study different algorithms for 4DCBCT reconstruction and DIR were evaluated...
November 14, 2018: Zeitschrift Für Medizinische Physik
Heiko Neeb, Jochen Schenk
OBJECTIVES: The current work investigates the performance of different multivariate supervised machine learning models to predict the presence or absence of multiple sclerosis (MS) based on features derived from quantitative MRI acquisitions. The performance of these models was evaluated for images which are significantly degraded due to subject motion, a problem which is often observed in clinical routine diagnostics. Finally, the difference between a true multivariate analysis and the corresponding univariate analysis based on single parameters alone was addressed...
November 12, 2018: Zeitschrift Für Medizinische Physik
Christopher Kurz, Philipp Süss, Carolin Arnsmeyer, Jonas Haehnle, Katrin Teichert, Guillaume Landry, Jan Hofmaier, Florian Exner, Lucas Hille, Florian Kamp, Christian Thieke, Ute Ganswindt, Chiara Valentini, Tobias Hölscher, Esther Troost, Mechthild Krause, Claus Belka, Karl-Heinz Küfer, Katia Parodi, Christian Richter
Proton radiotherapy (PT) requires accurate target alignment before each treatment fraction, ideally utilizing 3D in-room X-ray computed tomography (CT) imaging. Typically, the optimal patient position is determined based on anatomical landmarks or implanted markers. In the presence of non-rigid anatomical changes, however, the planning scenario cannot be exactly reproduced and positioning should rather aim at finding the optimal position in terms of the actually applied dose. In this work, dose-guided patient alignment, implemented as multicriterial optimization (MCO) problem, was investigated in the scope of intensity-modulated and double-scattered PT (IMPT and DSPT) for the first time...
November 5, 2018: Zeitschrift Für Medizinische Physik
Martin Fiebich, Ulrich Wolf
No abstract text is available yet for this article.
October 29, 2018: Zeitschrift Für Medizinische Physik
Giulio Rossi, Mark Gainey, Benedikt Thomann, Michael Kollefrath, Jan Würfel, Bernd Allgaier, Dimos Baltas
The purpose of this study was to investigate the suitability of the microDiamond detector (mDD) type 60019 (PTW-Freiburg, Germany) for radial dose function measurements with High Dose Rate (HDR) 192 Ir brachytherapy sources. An HDR 192 Ir source model mHDR v2r (Nucletron BV, an Elekta company, The Netherlands) was placed at the centre of a MP3 water phantom (PTW-Freiburg, Germany) within a 4F needle. Three mDDs were employed to measure the radial dose function of the source by acquiring profiles along the source transverse axis...
October 16, 2018: Zeitschrift Für Medizinische Physik
L R Buschle, T Kampf, F T Kurz, V J F Sturm, M Pham, H-P Schlemmer, C H Ziener
Quantitative susceptibility mapping provides a measure for the local susceptibility within a voxel in magnetic resonance imaging (MRI). So far, theoretical and numerical studies focus on the assumption of a constant susceptibility inside each MR voxel. For blood vessel networks, however, susceptibility differences between blood and surrounding tissue occur on a much smaller length scale than the typical voxel size in routine MRI. In this work, the dependency of the quantitative susceptibility value on vessel size and voxel size is analyzed...
October 10, 2018: Zeitschrift Für Medizinische Physik
P Schick, H Gottschlag, O Fielitz, W Budach, I Simiantonakis
The University Hospital of Düsseldorf, Germany (UKD) recently installed the Respiratory Gating for Scanners module (RGSC) (Varian Medical Systems, Palo Alto, USA). The aim of this article is to report on the commissioning and clinical implementation of the RGSC system. The steps encompassed the validation of the manufacturer's specifications including functionality tests using a commercial and in-house developed breathing phantom, to establish calibration procedures, and clinical workflow analysis involving breath acquisition and patient data evaluation...
October 8, 2018: Zeitschrift Für Medizinische Physik
Petros Martirosian, Rolf Pohmann, Christina Schraml, Martin Schwartz, Thomas Kuestner, Nina Franziska Schwenzer, Klaus Scheffler, Konstantin Nikolaou, Fritz Schick
PURPOSE: To investigate the capabilities of a modern pseudo-continuous arterial spin labeling (PCASL) technique for non-invasive assessment of the temporal and spatial distribution of the liver perfusion in healthy volunteers on a clinical MR system at 3T. MATERIALS AND METHODS: A 2D-PCASL multi-slice echo planar imaging sequence was adapted to the specific conditions in liver: a) labeling by PCASL was optimized to the flow characteristics in the portal vein, b) background suppression was applied for reduction of motion related artifacts, c) post labeling delays (PLDs) were varied over a large range (0...
September 25, 2018: Zeitschrift Für Medizinische Physik
G H Hartmann, P Andreo
Detailed information on the different methods used to compute charged-particle fluence spectra during a Monte Carlo (MC) calculation is scattered throughout the literature or discussed in internal reports. This work summarizes the most commonly used methods and introduces an alternative approach, makes comparisons between the different techniques, both from a theoretical ground and performing ad-hoc MC calculations, and discusses the advantages and constraints of each technique. It is concluded that methods based on the apportion of a track segment to the different energy bins of a linear or logarithmic grid are independent of the length of the track segment and the amount of energy loss between its extremes...
September 24, 2018: Zeitschrift Für Medizinische Physik
M Hillbrand, G Landry, S Ebert, G Dedes, E P Pappas, G Kalaitzakis, C Kurz, M Würl, F Englbrecht, O Dietrich, D Makris, E Pappas, K Parodi
Proton beams used for radiotherapy have potential for superior sparing of normal tissue, although range uncertainties are among the main limiting factors in the accuracy of dose delivery. The aim of this study was to benchmark an N-vinylpyrrolidone based polymer gel to perform three-dimensional measurement of geometric proton beam characteristics and especially to test its suitability as a range probe in combination with an anthropomorphic phantom. For single proton pencil beams as well as for 3×3cm2 mono-energy layers depth dose profiles, lateral dose distribution at different depths and proton range were evaluated in simple cubic gel phantoms at different energies from 75 to 115MeV and different dose levels...
September 21, 2018: Zeitschrift Für Medizinische Physik
Di Yan, Dietmar Georg
No abstract text is available yet for this article.
August 2018: Zeitschrift Für Medizinische Physik
Melisa Okanovic, Michael Völker, Robert Trampel, Felix Breuer, Peter Jakob, Martin Blaimer
PURPOSE: To improve a radial multi-slice 2D gradient- and spin-echo (GRASE) sequence and provide an appropriate image reconstruction technique for SAR-reduced high-resolution neuroimaging. METHODS: Additional readout gradients per radio-frequency (RF) refocusing allow for a reduced number of RF pulses. In this way, a specific absorption rate (SAR) reduction is achieved and the application at high-field systems becomes more feasible. A phase insensitive image reconstruction is proposed to reduce signal dropout artifacts originating from opposite readout polarities...
August 2018: Zeitschrift Für Medizinische Physik
Bin Cai, Olga L Green, Rojano Kashani, Vivian L Rodriguez, Sasa Mutic, Deshan Yang
The fast evolution of technology in radiotherapy (RT) enabled the realization of adaptive radiotherapy (ART). However, the new characteristics of ART pose unique challenges for efficiencies and effectiveness of quality assurance (QA) strategies. In this paper, we discuss the necessary QAs for ART and introduce a practical implementation. A previously published work on failure modes and effects analysis (FMEA) of ART is introduced first to explain the risks associated with ART sub-processes. After a brief discussion of QA challenges, we review the existing QA strategies and tools that might be suitable for each ART step...
August 2018: Zeitschrift Für Medizinische Physik
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