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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
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
Heide Meißner, Hermann Fuchs, Albert Hirtl, Christian Reschl, Markus Stock
No abstract text is available yet for this article.
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
Moritz Budde, Irenäus A Adamietz, Holger Sommer, Horst Hermani
The surgical removal of a breast tumour is often followed by postoperative irradiation of the surrounding tissue with a radioactive source (brachytherapy). When performing the MammoSite procedure, a spherical silicone balloon is inserted and filled with a NaCl solution. In a period of about five days in several sessions an iridium-192 source with high activity travels through a catheter into the balloon (afterloading) to irradiate the tumour cells remaining in the cavity. In this study, dose distributions of a MammoSite applicator are investigated based on measurements with a 2D detector array, Monte Carlo simulations and calculations with BrachyVision...
April 2018: Zeitschrift Für Medizinische Physik
Simon Howitz, Michael Schwedas, Tilo Wiezorek, Klemens Zink
Reference dosimetry by means of clinical linear accelerators in high-energy photon fields requires the determination of the beam quality specifier TPR20,10 , which characterizes the relative particle flux density of the photon beam. The measurement of TPR20,10 has to be performed in homogenous photon beams of size 10×10cm2 with a focus-detector distance of 100cm. These requirements cannot be fulfilled by TomoTherapy treatment units from Accuray. The TomoTherapy unit provides a flattening-filter-free photon fan beam with a maximum field width of 40cm and field lengths of 1...
April 2018: Zeitschrift Für Medizinische Physik
Yuvaraj Sekar, Johannes Thoelking, Miriam Eckl, Irakli Kalichava, Dwi Seno Kuncoro Sihono, Frank Lohr, Frederik Wenz, Hansjoerg Wertz
BACKGROUND AND PURPOSE: The novel MatriXXFFF (IBA Dosimetry, Germany) detector is a new 2D ionization chamber detector array designed for patient specific IMRT-plan verification including flattening-filter-free (FFF) beams. This study provides a detailed analysis of the characterization and clinical evaluation of the new detector array. MATERIAL AND METHODS: The verification of the MatriXXFFF was subdivided into (i) physical dosimetric tests including dose linearity, dose rate dependency and output factor measurements and (ii) patient specific IMRT pre-treatment plan verifications...
April 2018: Zeitschrift Für Medizinische Physik
Tina Pfeiler, Christian Bäumer, Erik Engwall, Dirk Geismar, Bernhard Spaan, Beate Timmermann
Respiratory induced organ motion poses a major challenge for high-precision radiotherapy such as pencil beam scanning proton therapy (PBS). In order to employ PBS for target regions affected by respiratory motion, the implementation of dedicated motion mitigation techniques should be considered and residual uncertainties need to be assessed. For the latter purpose, a routine simulating the delivery of a scanned proton beam to a moving target was developed and implemented in the commercial treatment planning system RayStation...
April 2018: Zeitschrift Für Medizinische Physik
Pascal Hauri, Uwe Schneider
PURPOSE: Long-term survivors of cancer who were treated with radiotherapy are at risk of a radiation-induced tumor. Hence, it is important to model the out-of-field dose resulting from a cancer treatment. These models have to be verified with measurements, due to the small size, the high sensitivity to ionizing radiation and the tissue-equivalent composition, LiF thermoluminescence dosimeters (TLD) are well-suited for out-of-field dose measurements. However, the photon energy variation of the stray dose leads to systematic dose errors caused by the variation in response with radiation energy of the TLDs...
April 2018: Zeitschrift Für Medizinische Physik
Thomas Kampf, Theresa Reiter, Wolfgang Rudolf Bauer
Quantitative nuclear magnetic resonance imaging (MRI) shifts more and more into the focus of clinical research. Especially determination of relaxation times without/and with contrast agents becomes the foundation of tissue characterization, e.g. in cardiac MRI for myocardial fibrosis. Techniques which assess longitudinal relaxation times rely on repetitive application of readout modules, which are interrupted by free relaxation periods, e.g. the Modified Look-Locker Inversion Recovery = MOLLI sequence. These discontinuous sequences reveal an apparent relaxation time, and, by techniques extrapolated from continuous readout sequences, a putative real T1 is determined...
April 2018: Zeitschrift Für Medizinische Physik
Di Yan, Dietmar Georg
No abstract text is available yet for this article.
March 27, 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...
March 23, 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...
March 14, 2018: Zeitschrift Für Medizinische Physik
Lorenzo Placidi, Michele Togno, Damien C Weber, Antony J Lomax, Jan Hrbacek
PURPOSE: Wedge phantoms coupled with a CCD camera are suggested as a simple means to improve the efficiency of quality assurance for pencil beam scanning (PBS) proton therapy, in particular to verify energy/range consistency on a daily basis. The method is based on the analysis of an integral image created by a pencil beam (PB) pattern delivered through a wedge. We have investigated the reproducibility of this method and its dependence on setup and positional beam errors for a commercially available phantom (Sphinx® , IBA Dosimetry) and CCD camera (Lynx® , IBA Dosimetry) system...
March 13, 2018: Zeitschrift Für Medizinische Physik
Thiago V M Lima, Silvano Gnesin, Nick Ryckx, Klaus Strobel, Nicolas Stritt, Reto Linder
A multidisciplinary working group led by the Swiss Federal Office of Public Health was formed to plan and perform a nationwide survey of patient radiation exposure from computed tomography (CT) in hybrid devices across Nuclear Medicine departments. The survey included 16 departments (of which 5 were university hospitals) and the submitted responses included 10,673 entries for the 33 different protocols proposed (11 in PET and 22 in SPECT). The working group determined the selection and exclusion criteria applied to the analysis...
February 17, 2018: Zeitschrift Für Medizinische Physik
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