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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
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
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
Björn Delfs, Ralf-Peter Kapsch, Ndimofor Chofor, Hui Khee Looe, Dietrich Harder, Björn Poppe
The frequently applied narrow and non-standard transverse dose profiles of intensity modulated photon-beam radiotherapy, lacking lateral secondary electron equilibrium, require the use of high-resolution dosimetry detectors, and small air-filled detectors are recommended as the reference detectors for cross-calibration of the high-resolution detectors. The present study focuses on the dosimetric properties of a novel cylindrical ionization chamber, the PTW Semiflex 3D 31021. The chamber's effective point of measurement was found to lie at (0...
June 4, 2018: Zeitschrift Für Medizinische Physik
Haroun Al-Mohamedi, Ismael Kelly-Pérez, Andreas Prinz, Theo Oltrup, Martin Leitritz, Alan Cayless, Thomas Bende
This study reviews the development of Swept-Source interferometers and compares systematically three different Swept-Source interferometer designs for biometric measurements of the eye. Principles characteristics, conveniences and accessibilities of the three developed systems are presented. The main difference between the three Swept-Source systems is the method of tuning the wavelength at the broadband optical amplifier. The implementation of a "quasi-phase-continuous method" (QPC) for wavelength tuning led to longer measuring depth but was more time-consuming...
June 1, 2018: Zeitschrift Für Medizinische Physik
Heide Meißner, Hermann Fuchs, Albert Hirtl, Christian Reschl, Markus Stock
The characteristic depth-dose profile of protons traveling through material is the main advantage of proton therapy over conventional radiotherapy with photons or electrons. However, uncertainties regarding the range of the protons in human tissue prevent to exploit the full potential of proton therapy. Therefore, a non-invasive in-vivo dose monitoring is desired. At the ion beam center MedAustron in Wiener Neustadt/Austria, patient treatment with proton beams started in December 2016. A PET/CT is available in close vicinity of the treatment rooms, exclusively dedicated to offline PET monitoring directly after the therapeutic irradiation...
May 30, 2018: Zeitschrift Für Medizinische Physik
Severin Kampfer, Nathan Cho, Stephanie E Combs, Jan J Wilkens
The aim of this study was to investigate a single crystal diamond detector, the microDiamond detector from PTW (PTW-Freiburg, Freiburg, Germany), concerning the particular requirements in the set-up and energy range used in small animal radiotherapy (RT) research (around 220kV). We tested it to find out the minimal required pre-irradiation dose, the dose linearity, dose rate dependency and the angular response as well as usability in the small animal radiation research platform, SARRP (Xstrahl Ltd., Camberley, UK)...
May 29, 2018: Zeitschrift Für Medizinische Physik
P Manser, D Frauchiger, D Frei, W Volken, D Terribilini, M K Fix
PURPOSE: Using volumetric modulated arc therapy (VMAT) delivery technique gantry position, multi-leaf collimator (MLC) as well as dose rate change dynamically during the application. However, additional components can be dynamically altered throughout the dose delivery such as the collimator or the couch. Thus, the degrees of freedom increase allowing almost arbitrary dynamic trajectories for the beam. While the dose delivery of such dynamic trajectories for linear accelerators is technically possible, there is currently no dose calculation and validation tool available...
April 6, 2018: Zeitschrift Für Medizinische Physik
Manuel Blessing, Anna Arns, Hansjoerg Wertz, Dzmitry Stsepankou, Judit Boda-Heggemann, Juergen Hesser, Frederik Wenz, Frank Lohr
PURPOSE: To establish a fully automated kV-MV CBCT imaging method on a clinical linear accelerator that allows image acquisition of thoracic targets for patient positioning within one breath-hold (∼15s) under realistic clinical conditions. METHODS AND MATERIALS: Our previously developed FPGA-based hardware unit which allows synchronized kV-MV CBCT projection acquisition is connected to a clinical linear accelerator system via a multi-pin switch; i.e. either kV-MV imaging or conventional clinical mode can be selected...
April 2018: Zeitschrift Für Medizinische Physik
Michael Bock
No abstract text is available yet for this article.
April 2018: Zeitschrift Für Medizinische Physik
Philipp Freislederer, Christian Heinz, Henrike von Zimmermann, Sabine Gerum, Falk Roeder, Michael Reiner, Matthias Söhn, Claus Belka, Katia Parodi
Respiratory motion remains a source of major uncertainties in radiotherapy. Respiratory correlated computed tomography (referred to as 4DCT) serves as one way of reducing breathing artifacts in 3D-CTs and allows the investigation of tumor motion over time. The quality of the 4DCT images depends on the data acquisition scheme, which in turn is dependent on the vendor. Specifically, the only way Toshiba Aquilion LB CT scanners can reconstruct 4DCTs is a cycle-based reconstruction using triggers provided by an external surrogate signal...
April 2018: Zeitschrift Für Medizinische Physik
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