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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
Gregor Bruggmoser, Rainer Saum, Rafael Kranzer
The aim of this technical communication is to provide correction factors for recombination and polarity effect for two new ionization chambers PTW PinPoint 3D (type 31022) and PTW Semiflex 3D (type 31021). The correction factors provided are for the (based on the) German DIN 6800-2 dosimetry protocol and the AAPM TG51 protocol. The measurements were made in filtered and unfiltered high-energy photon beams in a water equivalent phantom at maximum depth of the PDD and a field size on the surface of 10cm×10cm...
August 2018: Zeitschrift Für Medizinische Physik
Markus Stock, Dietmar Georg, Alexander Ableitinger, Andrea Zechner, Alexander Utz, Marta Mumot, Gabriele Kragl, Johannes Hopfgartner, Joanna Gora, Till Böhlen, Loïc Grevillot, Peter Kuess, Phil Steininger, Heinz Deutschmann, Stanislav Vatnitsky
The ratio of patients who need a treatment adaptation due to anatomical variations at least once during the treatment course is significantly higher in light ion beam therapy (LIBT) than in photon therapy. The ballistic behaviour of ion beams makes them more sensitive to changes. Hence, the delivery of LIBT has always been supported by state of art image guidance. On the contrary CBCT technology was adapted for LIBT quite late. Adaptive concepts are being implemented more frequently in photon therapy and also efficient workflows are needed for LIBT...
August 2018: Zeitschrift Für Medizinische Physik
Martin Buschmann, Katarina Majercakova, Alina Sturdza, Stephanie Smet, Dina Najjari, Michaela Daniel, Richard Pötter, Dietmar Georg, Yvette Seppenwoolde
BACKGROUND: Radiotherapy for cervix cancer is challenging in patients exhibiting large daily changes in the pelvic anatomy, therefore adaptive treatments (ART) have been proposed. The aim of this study was the clinical implementation and subsequent evaluation of plan-of-the-day (POTD)-ART for cervix cancer in supine positioning. The described workflow was based on standard commercial equipment and current quality assurance (QA) methods. MATERIALS AND METHODS: A POTD strategy, which employs a VMAT plan library consisting of an empty bladder plan, a full bladder plan and a motion robust backup plan, was developed...
August 2018: Zeitschrift Für Medizinische Physik
Daniela Poppinga, Björn Delfs, Jutta Meyners, Dietrich Harder, Björn Poppe, Hui Khee Looe
The first aim of this study has been to extend the systematic experimental study of the field size dependence of the output factor correction for three micro-ionization chambers (PTW 31014, PTW 31022 and IBA Razor chamber), two silicon diodes (PTW 60017 and IBA Razor Diode) and the synthetic diamond detector microDiamond (PTW 60019) in a 6 MV photon beam down to an effective field side length of 2.6mm, and to summarize the present knowledge of this factor by treating it as a function of the dosimetric field size...
August 2018: Zeitschrift Für Medizinische Physik
Daniela Thorwarth
The aim of biologically adapted radiotherapy (RT) is to shape or paint the prescribed radiation dose according to biological properties of the tumor in order to increase local control rates in the future. Human tumors are known to present with an extremely heterogeneous tissue architecture leading to highly variable local cell densities and chaotic vascular structures leading to tumor hypoxia and regions of increased radiation resistance. The goal of biologically adapted RT or dose painting is to individually adapt the radiation dose to biological features of the tumor as non-invasively assessed with functional imaging in order to overcome increased radiation resistance...
August 2018: Zeitschrift Für Medizinische Physik
Sonja Wegener, Stefan Weick, Otto A Sauer
PURPOSE: The characteristics of radiation detectors have to be assessed for dosimetry in the presence of magnetic fields, i.e. in conditions found in combined machines for magnetic resonance imaging and radiotherapy. While a lot of attention is directed toward correction factors for absolute dosimetry in magnetic fields, relative dose measurements are an equally important task to be performed. There is a need to experimentally analyze detector response differences in the build-up region in the presence of a transverse magnetic field...
July 23, 2018: Zeitschrift Für Medizinische Physik
D Kretz, J Hesser, G Glatting, S Diehl, F Wenz, W He, L Zheng
For selective internal radiation therapy (SIRT) the calculation of the 3D distribution of spheres based on individual blood flow properties is still an open and relevant research question. The purpose of this work is to develop and analyze a new treatment planning method for SIRT to calculate the absorbed dose distribution. For this intention, flow dynamics of the SIRT-spheres inside the blood vessels was simulated. The challenge is treatment planning solely using high-resolution imaging data available before treatment...
July 23, 2018: Zeitschrift Für Medizinische Physik
Frank Wolfram, Thomas G Lesser
Recent work has shown that One Lung Flooding (OLF) enables acoustic access to central lung tumours which can be used for non-invasive ablation using therapeutic ultrasound (HIFU). Therefore acoustic properties of flooded lung as a saline-tissue compound was determined in earlier work, which revealed that atypical acoustical condition in lung exists. Their influence on the HIFU ablation process under aspects of clinical requirements has to be investigated before clinical introduction. For this study a MATLAB based ultrasound simulation tool and a customized bioheat solver were used to determine the temporal course of HIFU induced heating with the corresponding ablation zones...
July 20, 2018: Zeitschrift Für Medizinische Physik
Fabian Tobias Gutjahr, Eberhard Munz, Peter Michael Jakob
PURPOSE: A new chemical exchange MRI method is proposed which allows for direct detection of exchanging solute protons with concurrent water background suppression. METHODS: The proposed method, RACETE (Refocused Acquisition of Chemical Exchange Transferred Excitations), is based on a stimulated-echo-technique, where the first two excitation pulses are replaced by a train of N solute-selective excitation-transfer modules. This excitation cycle is then followed by a stimulated echo acquisition via selective refocusing of exchanged solute protons now present in the solvent pool...
June 12, 2018: Zeitschrift Für Medizinische Physik
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