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Physics in Medicine and Biology

Li Tao, Kun Zhu, Jungao Zhu, Xiaohan Xu, Chen Lin, Wenjun Ma, Haiyang Lu, Yanying Zhao, Yuanrong Lu, Jia-Er Chen, Xueqing Yan
With the development of laser technology, laser-driven proton acceleration provides a new way for proton tumor therapy. However, it has not been applied in practice, because of the wide and decreasing energy spectrum of laser-accelerated proton beams. In this paper, we propose an analytical model to reconstruct the spread-out Bragg peak (SOBP) using the laser-accelerated proton beams. Firstly, we present a modified weighting formula for protons of different energies. Secondly, a theoretical model for the reconstruction of SOBPs with laser-accelerated proton beams has been built...
April 27, 2017: Physics in Medicine and Biology
Hongcheng Liu, Peng Dong, Lei Xing
Traditional inverse planning relies on the use of weighting factors to balance the conflicting requirements of different structures. The manual trial-and-error determination of the weighting factors has long been recognized as a time-consuming part of treatment planning. The purpose of this work is to develop an inverse planning framework that parameterizes the dosimetric tradeoff among the structures with physically meaningful quantities to simplify the search for clinically sensible plans. In this formalism, instead of using the weighting factors, permissible variation range of the prescription dose or dose volume histogram (DVH) of the involved structures are used to characterize the "importance" of the structures...
April 27, 2017: Physics in Medicine and Biology
Calyn R Moulton, Michael J House, Victoria Lye, Colin I Tang, Michele Krawiec, David J Joseph, James W Denham, Martin A Ebert
This study investigates the associations between spatial distribution of dose to the rectal surface and observed gastrointestinal toxicities after deformably registering each phase of a combined external beam radiotherapy (EBRT)/high-dose-rate brachytherapy (HDRBT) prostate cancer treatment. The study contains data for 118 patients where the HDRBT CT was deformably-registered to the EBRT CT. The EBRT and registered HDRBT TG43 dose distributions in a reference 2 Gy/fraction were 3D-summed. Rectum dose-surface maps (DSMs) were obtained by virtually unfolding the rectum surface slice-by-slice...
April 26, 2017: Physics in Medicine and Biology
Jarno van Roosmalen, Marlies C Goorden
Accurate analytical expressions for collimator resolution and sensitivity are important tools in the optimization of SPECT systems. However, presently known expressions for the sensitivity of converging collimators either diverge near the focal point or focal line(s), or are only valid on the collimator axis. As a result, these expressions are unsuitable to calculate volumetric sensitivity for e.g. short-focal length collimators that focus inside the object to enhance sensitivity. To also enable collimator optimization for these geometries, we here present non-diverging sensitivity formulas for astigmatic, cone beam and fan beam collimators that are applicable over the full collimator's field-of-view...
April 26, 2017: Physics in Medicine and Biology
Hyo-Min Cho, Huanjun Ding, Nikita Kumar, David Sennung, Sabee Molloi
The aim of this study is to investigate the feasibility of water and lipid as calibration phantoms for accurate dual energy breast density quantification. Dual energy calibration was performed on a mammography system based on scanning multi-slit Si strip photon-counting detectors using plastic water and adipose-equivalent phantoms as the basis materials. Two different methods were used to convert the dual energy decomposition measurements in plastic phantom thicknesses into the true water and lipid basis materials...
April 25, 2017: Physics in Medicine and Biology
Kleopatra Pirpinia, Peter Bosman, Claudette Loo, Gonneke Winter-Warnars, Natasja Janssen, Astrid Scholten, Jan-Jakob Sonke, Marcel van Herk, Tanja Alderliesten
Deformable image registration is typically formulated as an optimization problem involving a linearly weighted combination of terms that correspond to objectives of interest (e.g., similarity, deformation magnitude). The weights, along with multiple other parameters, need to be manually tuned for each application, a task currently mainly addressed via trial-and-error approaches. Such approaches can only be successful if there is a sensible interplay between parameters, objectives, and desired registration outcome...
April 24, 2017: Physics in Medicine and Biology
Daniela M Wagner, Petra Huettenrauch, Mathias Anton, Philip von Voigts-Rhetz, Klemens Zink, Hendrik Wolff
PURPOSE: The Physikalisch-Technische Bundesanstalt (PTB) has established a secondary standard measurement system for the dose to water, DW, based on alanine/ ESR (Anton et. al. 2013). The aim of this study was to test the established measurements system for out of field measurements inpatient with breast cancer. METHOD AND MATERIALS: A set of five alanine pellets were affixed to each patients` skin at the contra lateral breast beginning at the sternum and extending over the mammilla to the distal surface...
April 24, 2017: Physics in Medicine and Biology
Stefano Pedemonte, Larry Pierce, Koen Van Leemput
Measuring the depth-of-interaction (DOI) of gamma photons enables increasing the resolution of emission imaging systems. Several design variants of DOI-sensitive detectors have been recently introduced to improve the performance of scanners for Positron Emission Tomography (PET). However, the accurate characterization of the response of DOI detectors, necessary to accurately measure the DOI, remains an unsolved problem. Numerical simulations are, at the state of the art, imprecise, while measuring directly the characteristics of DOI detectors experimentally is hindered by the impossibility to impose the depth-of-interaction in an experimental set-up...
April 24, 2017: Physics in Medicine and Biology
Beatrice Berthon, Pierre-Marc Dansette, Mickael Tanter, Mathieu Pernot, Jean Provost
PURPOSE: Direct imaging of cardiac electrical activation is crucial to better understand and diagnose diseases linked to arrhythmias. This work presents an Ultrafast Acoustoelectric Imaging (UAI) system for direct and non-invasive ultrafast mapping of propagating current densities. MATERIALS AND METHODS: Acoustoelectric imaging is based on the acoustoelectric effect, the modulation of the medium's electrical impedance by a propagating ultrasonic wave. UAI triggers this effect with plane wave emissions to image current densities...
April 24, 2017: Physics in Medicine and Biology
Yu Liu, Jingfei Liu, Brett Z Fite, Josquin Foiret, Asaf Ilovitsh, J Kent Leach, Erik Dumont, Charles F Caskey, Katherine W Ferrara
Non-invasive, quantitative methods to assess the properties of biological tissues are needed for many therapeutic and tissue engineering applications. Magnetic resonance elastography (MRE) has historically relied on external vibration to generate periodic shear waves. In order to focally assess a biomaterial or to monitor the response to ablative therapy, the interrogation of a specific region of interest by a focused beam is desirable and transient MRE (t-MRE) techniques have previously been developed to accomplish this goal...
April 20, 2017: Physics in Medicine and Biology
Ye Zhang, Isabel Huth, Martin Wegner, Damien C Weber, Antony J Lomax
This simulation study investigated the dosimetric effectiveness and treatment efficiency of surface motion guided gating of pencil beam scanning (PBS) proton therapy for liver tumour treatments. Dedicated 4D dose calculations were performed for simulating gated treatments using 4DCT data for six patients derived from 4DMRI (4DCT(MRI)). Surface motion as a surrogate for tumour motion was extracted from the 4DMRI images and a linear internal-external correlation model applied to derive amplitude-based gating windows (GWs) of 10 and 5 mm...
April 20, 2017: Physics in Medicine and Biology
Yuhe Wang, Thomas Mazur, Justin Park, Deshan Yang, Sasa Mutic, H Harold Li
Online adaptive radiation therapy (ART) based on real-time magnetic resonance imaging represents a paradigm-changing treatment scheme. However, conventional quality assurance (QA) methods based on phantom measurements are not feasible with the patient on the treatment couch. The purpose of this work is to develop a fast Monte Carlo system for validating online re-optimized tri-60Co IMRT adaptive plans with both high accuracy and speed. The Monte Carlo system is based on Dose Planning Method (DPM) code with further simplification of electron transport and consideration of external magnetic fields...
April 20, 2017: Physics in Medicine and Biology
John S Ginn, Nzhde Agazaryan, Minsong Cao, Umar Baharom, Daniel Low, Yingli Yang, Yu Gao, Peng Hu, Percy Lee, James Lamb
Spatial distortion results in image deformation that can degrade accurate targeting and dose calculations in MRI-guided adaptive radiotherapy. The authors present a comprehensive assessment of a 0.35T MRI-guided radiotherapy system's spatial distortion using two commercially-available phantoms with regularly spaced markers. Images of the spatial integrity phantoms were acquired using five clinical protocols on the MRI-guided radiotherapy machine with the radiotherapy gantry positioned at various angles. Software was developed to identify and localize all phantom markers using a template matching approach...
April 20, 2017: Physics in Medicine and Biology
T Tessonnier, A Mairani, S Brons, T Haberer, J Debus, K Parodi
At the Heidelberg Ion Beam Therapy Center, scanned helium and oxygen ion beams are available in addition to the clinically used protons and carbon ions for physical and biological experiments. In this work, a study of the basic dosimetric features of the different ions is performed in the entire therapeutic energy range. Depth dose distributions are investigated for pencil-like beam irradiation, with and without a modulating ripple filter, focusing on the extraction of key Bragg curve parameters, such as the range, the peak-width and the distal 80%-20% fall-off...
April 13, 2017: Physics in Medicine and Biology
Min Sun Lee, Kyeong Yun Kim, Guen Bae Ko, Jae Sung Lee
In this study, we developed a proof-of-concept prototype PET system using a pair of depth-of-interaction (DOI) PET detectors based on the proposed DOI-encoding method and digital silicon photomultiplier (dSiPM). Our novel cost-effective DOI measurement method is based on a triangular-shaped reflector that requires only a single-layer pixelated crystal and single-ended signal readout. The DOI detector consisted of an 18  ×  18 array of unpolished LYSO crystal (1.47  ×  1.47  ×  15 mm(3)) wrapped with triangular-shaped reflectors...
April 13, 2017: Physics in Medicine and Biology
Steven E Vigdor, Alexander Klyachko, Keith Solberg, Mark Pankuch
In order to address dosimetry demands during proton therapy treatments utilizing pencil beam scanning and/or pulsed beam accelerators, we have developed a xenon-filled Gas Scintillation Detector (GSD) that can monitor delivered dose and two-dimensional beam centroid position pulse-by-pulse in real time, with high response linearity up to high instantaneous dose rates. We present design considerations for the GSD and results of beam tests carried out at operating proton therapy clinics. In addition to demonstrating spatial resolution with σ of a few hundred microns in each transverse dimension and relative dose precision better than 1% over large treatment areas, the test beam results also reveal the dependence of the GSD dose normalization on dose rate, beam energy, and gas impurities...
April 12, 2017: Physics in Medicine and Biology
Mengxi Zhang, Jian Zhou, Xiaofeng Niu, Evren Asma, Wenli Wang, Jinyi Qi
Penalized likelihood (PL) reconstruction has demonstrated potential to improve image quality of positron emission tomography (PET) over unregularized ordered-subsets expectation-maximization (OSEM) algorithm. However, selecting proper regularization parameters in PL reconstruction has been challenging due to the lack of ground truth and variation of penalty functions. Here we present a method to choose regularization parameters using a cross-validation log-likelihood (CVLL) function. This new method does not require any knowledge of the true image and is directly applicable to list-mode PET data...
April 12, 2017: Physics in Medicine and Biology
Jeffrey Martin Cochran, So Chung, Anaïs Leproux, Wesley Baker, David Busch, Angela DeMichele, Julia Tchou, Bruce Tromberg, Arjun Yodh
We measure tissue blood flow markers in breast tumors during neoadjuvant chemotherapy and investigate their correlation to pathologic complete response in a pilot longitudinal patient study (n=4). Tumor blood flow is quantified optically by diffuse correlation spectroscopy (DCS), and tissue optical properties, blood oxygen saturation, and total hemoglobin concentration are derived from concurrent diffuse optical spectroscopic imaging (DOSI). The study represents the first longitudinal DCS measurement of neoadjuvant chemotherapy in humans over the entire course of treatment; it therefore offers a first correlation between DCS flow indices and pathologic complete response...
April 12, 2017: Physics in Medicine and Biology
Giovanni Mettivier, Kristina Bliznakova, Ioannis Sechopoulos, John Boone, Francesca Di Lillo, Antonio Sarno, Roberta Castriconi, Paolo Russo
The aim of this work is the evaluation of the software BreastSimulator, a breast X-ray imaging simulation software as a tool for the creation of 3D uncompressed breast digital models and for the simulation and the optimization of computed tomographic (CT) scanners dedicated to the breast. Eight 3D digital breast phantoms were created with glandular fraction in the range 10% to 68%. The models are characterised by different sizes and modelled realistic anatomical features.. X-ray CT projections were simulated for a dedicated cone-beam CT scanner and reconstructed with the FDK algorithm...
April 11, 2017: Physics in Medicine and Biology
Emilie Roncali, Mariele Stockhoff, Simon Cherry
Accurately modeling the light transport in scintillation detectors is essential to design new detectors for nuclear medicine or high energy physics. Optical models implemented in software such as Geant4 and GATE suffer from important limitations that we addressed by implementing a new approach in which the crystal reflectance was computed from 3D surface measurements. The reflectance was saved in a look-up-table (LUT) then used in Monte Carlo simulation to determine the fate of optical photons. Our previous work using this approach demonstrated excellent agreement with experimental characterization of crystal light output in a limited configuration, i...
April 11, 2017: Physics in Medicine and Biology
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