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Physics in Medicine and Biology

Koki Ando, Mitsutaka Yamaguchi, Seiichi Yamamoto, Toshiyuki Toshito, Naoki Kawachi
Imaging of secondary electron bremsstrahlung x-ray emitted during proton irradiation is a possible method for measurement of the proton beam distribution in phantom. However, it is not clear that the method is used for range estimation of protons. For this purpose, we developed a low-energy x-ray camera and conducted imaging of the bremsstrahlung x-ray produced during irradiation of proton beams. We used a 20 mm  ×  20 mm  ×  1 mm finely grooved GAGG scintillator that was optically coupled to a one-inch square high quantum efficiency (HQE)-type position-sensitive photomultiplier tube to form an imaging detector...
May 22, 2017: Physics in Medicine and Biology
Bassim Aklan, Pia Gierse, Josefin Hartmann, Oliver J Ott, Rainer Fietkau, Christoph Bert
Patient positioning plays an important role in regional deep hyperthermia to obtain a successful hyperthermia treatment. In this study, the influence of possible patient mispositioning was systematically assessed on specific absorption rate (SAR) and temperature distribution. With a finite difference time domain approach, the SAR and temperature distributions were predicted for six patients at 312 positions. Patient displacements and rotations as well as the combination of both were considered inside the Sigma-Eye applicator...
May 22, 2017: Physics in Medicine and Biology
Mehdi Mahnam, Michel Gendreau, Nadia Lahrichi, Louis-Martin Rousseau
In this paper, we propose a novel heuristic algorithm for the volumetric modulated arc therapy (VMAT) treatment planning problem, optimizing the trade-off between delivery time and treatment quality. We present a new mixed integer programming model in which the multi-leaf collimator leaf positions, gantry speed, and dose rate are determined simultaneously. Our heuristic is based on column generation; the aperture conguration is modeled in the columns and the dose distribution and time restriction in the rows...
May 19, 2017: Physics in Medicine and Biology
Silin Ren, Xiao Jin, Chung Chan, Yiqiang Jian, Tim Mulnix, Chi Liu, Richard E Carson
Data-driven respiratory gating techniques were developed to correct for respiratory motion in PET studies, without the help of external motion tracking systems. Due to the greatly increased image noise in gated reconstructions, it is desirable to develop a data-driven event-by-event respiratory motion correction method. In this study, using the Centroid-of-distribution (COD) algorithm, we established a data-driven event-by-event respiratory motion correction technique using TOF PET list-mode data, and investigated its performance by comparing with an external system-based correction method...
May 18, 2017: Physics in Medicine and Biology
Rebekah H Griesenauer, Jared A Weis, Lori R Arlinghaus, Ingrid M Meszoely, Michael I Miga
Tissue stiffness interrogation is fundamental in breast cancer diagnosis and treatment. Furthermore, biomechanical models for predicting breast deformations have been created for several breast cancer applications. Within these applications, constitutive mechanical properties must be defined and the accuracy of this estimation directly impacts the overall performance of the model. In this study, we present an image-derived computational framework to obtain quantitative, patient specific stiffness properties for application in image-guided breast cancer surgery and interventions...
May 18, 2017: Physics in Medicine and Biology
Mary Germino, Jean-Dominique Gallezot, Jianhua Yan, Richard Carson
Parametric images for dynamic positron emission tomography (PET) are typically generated by an indirect method, i.e., reconstructing a time series of emission images, then fitting a kinetic model to each voxel time activity curve. Alternatively, "direct reconstruction," incorporates the kinetic model into the reconstruction algorithm itself, directly producing parametric images from projection data. Direct reconstruction has been shown to achieve parametric images with lower standard error than the indirect method...
May 15, 2017: Physics in Medicine and Biology
Severine Rossomme, Julian Horn, Stephan Brons, Oliver Jaekel, Andrea Mairani, Mario Ciocca, Vincent Floquet, Francesco Romano, Diana Rodriguez Garcia, Stefaan Vynckier, Hugo Palmans
Based on international reference dosimetry protocols for light-ion beams, a correction factor (<i>k<sub>s</sub></i>) has to be applied to the response of a plane-parallel ionisation chamber, to account for recombination of negative and positive charges in its air cavity before these charges can be collected on the electrodes. In this work, <i>k<sub>s</sub></i> for IBA PPC40 Roos-type chambers is investigated in four scanned light-ion beams (proton, helium, carbon and oxygen)...
May 15, 2017: Physics in Medicine and Biology
Peter Simon Potrebko, Jason Fiege, Matthew Biagioli, Jan Poleszczuk
Radiation Oncology treatment planning requires compromises to be made between clinical objectives that are invariably in conflict. It would be beneficial to have a "bird's-eye-view" perspective of the full spectrum of treatment plans that represent the possible trade-offs between delivering the intended dose to the planning target volume (PTV) while optimally sparing the organs-at-risk (OARs). In this work, the authors demonstrate Pareto-Aware Radiotherapy Evolutionary Treatment Optimization (PARETO), a multi-objective tool featuring such bird's-eye-view functionality, which optimizes fluence patterns and beam angles for intensity-modulated radiation therapy (IMRT) treatment planning...
May 11, 2017: Physics in Medicine and Biology
Abdella M Ahmed, Hideaki Tashima, Eiji Yoshida, Fumihiko Nishikido, Taiga Yamaya
There is a growing interest in developing brain PET scanners with high sensitivity and high spatial resolution for early diagnosis of neurodegenerative diseases and studies of brain functions. Sensitivity of the PET scanner can be improved by increasing the solid angle. However, conventional PET scanners are designed based on a cylindrical geometry, which may not be the most efficient design for brain imaging in terms of the balance between sensitivity and cost. We proposed a dedicated brain PET scanner based on a hemispheric shape detector and a chin detector (referred to as the helmet-chin PET), which is designed to maximize the solid angle by increasing the number of lines-of-response in the hemisphere...
May 10, 2017: Physics in Medicine and Biology
Petr Smirnov, Kullervo Hynynen
Deep Venous Thrombosis of the iliofemoral veins is a common and morbid disease, with the recommended interventional treatment carrying a high risk of hemorrhaging and complications. High Intensity Focused Ultrasound delivered with a single element transducer has been shown to successfully precipitate thrombolysis non-invasively in vitro and in vivo. However, in all previous studies damage to the veins or surrounding tissue has been observed. Using a simulation model of the human thigh, this study investigated whether a phased array device could overcome the large focal region limitations faced by single transducer treatment devices...
May 9, 2017: Physics in Medicine and Biology
Chris McIntosh, Mattea Welch, Andrea McNiven, David Jaffray, Thomas Purdie
Recent works in automated radiotherapy treatment planning have used machine learning based on historical treatment plans to infer the spatial dose distribution for a novel patient directly from the planning image. We present a probabilistic, atlas-based approach which predicts the dose for novel patients using a set of automatically selected most similar patients (atlases). The output is a spatial dose objective, which specifies the desired dose-per-voxel, and therefore replaces the need to specify and tune dose-volume objectives...
May 9, 2017: Physics in Medicine and Biology
Antti Juhani Kulmala, Mikko Tenhunen
The aim of this paper is to study a radial response model as a method, to correct output factor results gathered with ionization chambers of different size and shape in cone collimated RT fields. An enhanced version of a non-parametric super-resolution deconvolution method able to model a radial response function of a small cylinder symmetric ionization chamber is described and demonstrated. The radial response of four ionization chambers with different geometry and radius are estimated using 6 MV photon beam in water at the isocentre plane...
May 9, 2017: Physics in Medicine and Biology
Gabriel Famulari, Piotr Pater, Shirin Enger
PURPOSE: The aim of this study was to calculate microdosimetric distributions for low energy electrons simulated using the Monte Carlo track structure code Geant4-DNA. MATERIALS AND METHODS: Tracks for monoenergetic electrons with kinetic energies ranging from 100 eV to 1 MeV were simulated in an infinite spherical water phantom using the Geant4-DNA extension included in Geant4 toolkit version 10.2 (patch 02). The microdosimetric distributions were obtained through random sampling of transfer points and overlaying scoring volumes within the associated volume of the tracks...
May 9, 2017: Physics in Medicine and Biology
Muhammad Muinul Islam, Tetsuya Tsujikawa, Tetsuya Mori, Yasushi Kiyono, Hidehiko Okazawa
A noninvasive method to estimate input function directly from H2(15)O brain PET data for measurement of cerebral blood flow (CBF) was proposed in this study. The image derived input function (IDIF) method extracted the time-activity curves (TAC) of the major cerebral arteries at the skull base from the dynamic PET data. The extracted primordial IDIF showed almost the same radioactivity as the arterial input function (AIF) from sampled blood at the plateau part in the later phase, but significantly lower radioactivity in the initial arterial phase compared with that of AIF-TAC...
May 8, 2017: Physics in Medicine and Biology
Bassim Aklan, Josefin Hartmann, Diana Zink, Hadi Siavooshhaghighi, Ricarda Merten, Florian Putz, Oliver Ott, Rainer Fietkau, Christoph Bert
The aim of this study was to systematically investigate the influence of the inter- and intra-observer segmentation variation of tumors and organs at risk on the simulated temperature coverage of the target. CT scans of six patients with tumors in the pelvic region acquired for radiotherapy treatment planning were used for hyperthermia treatment planning. To study the effect of inter-observer variation, three observers manually segmented in the CT images of each patient the following structures: fat, muscle, bone and the bladder...
May 8, 2017: Physics in Medicine and Biology
Rens van Haveren, Włodzimierz Ogryczak, Gerda M Verduijn, Marleen Keijzer, Ben J M Heijmen, Sebastiaan Breedveld
Previously, we have proposed Erasmus-iCycle, an algorithm for fully automated IMRT plan generation based on prioritised (lexicographic) multi-objective optimisation with the 2-phase ϵ-constraint (2pϵc) method. For each patient, the output of Erasmus-iCycle is a clinically favourable, Pareto optimal plan. The 2pϵc method uses a list of objective functions that are consecutively optimised, following a strict, user-defined prioritisation. The novel lexicographic reference point method (LRPM) is capable of solving multi-objective problems in a single optimisation, using a fuzzy prioritisation of the objectives...
May 5, 2017: Physics in Medicine and Biology
Gustavo Kertzscher, Sam Beddar
The availability of real-time treatment verification during high-dose-rate (HDR) brachytherapy is currently limited. Therefore, we studied the luminescence properties of the widely commercially available scintillators using the inorganic materials Eu-activated phosphors Y<sub>2</sub>O<sub>3</sub>:Eu, YVO<sub>4</sub>:Eu, Y<sub>2</sub>O<sub>2</sub>S:Eu, and Gd<sub>2</sub>O<sub>2</sub>S:Eu to determine whether they could be used to accurately and precisely verify HDR brachytherapy doses in real time...
May 5, 2017: Physics in Medicine and Biology
Hualiang Zhong, Indrin J Chetty
Tumor regression during the course of fractionated radiotherapy confounds the ability to accurately estimate the total dose delivered to tumor targets. Here we present a new criterion to improve the accuracy of image intensity-based dose mapping operations for adaptive radiotherapy for patients with non-small cell lung cancer (NSCLC). Six NSCLC patients were retrospectively investigated in this study. An image intensity-based B-spline registration algorithm was used for deformable image registration (DIR) of weekly CBCT images to a reference image...
May 5, 2017: Physics in Medicine and Biology
Andre Z Kyme, Martin Judenhofer, Kuang Gong, Julien Bec, Aaron Selfridge, Junwei Du, Jinyi Qi, Simon Cherry, Steven Meikle
'Open-field' PET, where an animal can move freely during imaging, enables functional changes in the brain to be correlated with an animal's behavioural response to environmental or pharmacologic stimuli. Previously we showed the feasibility of this technique for rats by applying motion compensation techniques to a commercially available scanner. However, this approach is limited by the scanner's inherent geometric and performance constraints. The goal of this project is to develop a purpose-built open-field PET system, based on an innovative sliding tomograph concept, optimised for imaging the mouse brain...
May 5, 2017: Physics in Medicine and Biology
Ricky T O'Brien, Uros Stankovic, Jan-Jakob Sonke, Paul J Keall
Four dimensional cone beam computed tomography (4DCBCT) uses a constant gantry speed and imaging frequency that are independent of the patient's breathing rate. Using a technique called respiratory motion guided 4DCBCT (RMG-4DCBCT), we have previously demonstrated that by varying the gantry speed and imaging frequency, in response to changes in the patient's real-time respiratory signal, the imaging dose can be reduced by 50-70%. RMG-4DCBCT optimally computes a patient specific gantry trajectory to eliminate streaking artefacts and projection clustering that is inherent in 4DCBCT imaging...
May 5, 2017: Physics in Medicine and Biology
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