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Medical Physics

Ethan Leng, Benjamin Spilseth, Lin Zhang, Jin Jin, Joseph S Koopmeiners, Gregory J Metzger
PURPOSE: Computer-aided detection/diagnosis (CAD) of prostate cancer (PCa) on multipara-metric MRI (mpMRI) is an active area of research. In the literature, the performance of predictive models trained to detect PCa on mpMRI has typically been reported in terms of voxel-wise mea-sures such as sensitivity and specificity and/or area under the receiver operating curve (AUC).However, it is unclear whether models that score higher by these measures are actually superior.Here, we propose a novel method for lesion identification as well as novel measures that assess the quality of the detected lesions...
March 15, 2018: Medical Physics
John W Garrett, Yinsheng Li, Ke Li, Guang-Hong Chen
PURPOSE: Digital breast tomosynthesis (DBT) has been shown to somewhat alleviate the breast tissue overlapping issues of two dimensional (2D) mammography.However, the improvement in current DBT systems over mammography is still limited.Statistical image reconstruction (SIR) methods have the potential to reduce through-plane artifacts in DBT, and thus may be used to further reduce anatomical clutter. The purpose of this work was to study the impact of SIR on anatomical clutter in the reconstructed DBT image volumes...
March 15, 2018: Medical Physics
Nathan Cho, Panagiotis Tsiamas, Esteban Velarde, Erik Tryggestad, Robert Jacques, Ross Berbeco, Todd McNutt, Peter Kazanzides, John Wong
PURPOSE: The Small Animal Radiation Research Platform (SARRP) has been developed for conformal micro irradiation with on-board cone-beam CT (CBCT) guidance. The graphics processing unit (GPU)-accelerated Superposition-Convolution (SC) method for dose computation has been integrated into the treatment planning system (TPS) for SARRP. This paper describes the validation of the SC method for the kilovoltage energy by comparing with EBT2 film measurements and Monte Carlo (MC) simulations...
March 15, 2018: Medical Physics
Alfredo Mirandola, Giuseppe Magro, Marco Lavagno, Andrea Mairani, Silvia Molinelli, Stefania Russo, Edoardo Mastella, Alessandro Vai, Davide Maestri, Vanessa La Rosa, Mario Ciocca
PURPOSE: To dosimetrically characterize a multi-layer ionization chamber (MLIC) prototype for quality assurance (QA) of pristine integral ionization curves (ICs) and spread-out-Bragg-peaks (SOBPs) for scanning light ion beams. METHODS: QUBE (De.Tec.Tor., Torino, Italy) is a modular detector designed for QA in particle therapy (PT). Its main module is a MLIC detector, able to evaluate particle beam relative depth ionization distributions at different beam energies and modulations...
March 14, 2018: Medical Physics
James R Kerns, David Followill, Jessica Lowenstein, Andrea Molineu, Paola Alvarez, Paige A Taylor, Stephen F Kry
PURPOSE: Reference dosimetry data can provide an independent second check of acquired values when commissioning or validating a treatment planning system (TPS). The Imaging and Radiation Oncology Core at Houston (IROC-Houston) has measured numerous linear accelerators throughout its existence. The results of those measurements are given here, comparing accelerators and the agreement of measurement versus institutional TPS calculations. METHODS: Data from IROC-Houston on-site reviews from 2000 through 2014 were analyzed for all Elekta accelerators, approximately 50...
March 14, 2018: Medical Physics
Katsuyuki Taguchi, Karl Stierstorfer, Christoph Polster, Okkyun Lee, Steffen Kappler
PURPOSE: The inter-pixel cross-talk of energy-sensitive photon counting x-ray detectors (PCDs) has been studied and an analytical model (version 2.1) has been developed for double-counting between neighboring pixels due to charge sharing and K-shell fluorescence x-ray emission followed by its re-absorption [Taguchi K, et al., Medical Physics 2016;43(12):6386-6404]. While the model version 2.1 simulated the spectral degradation well, it had the following problems that has been found to be significant recently: (1) The spectrum is inaccurate with smaller pixel sizes; (2) the charge cloud size must be smaller than the pixel size; (3) the model underestimates the spectrum/counts for 10-40 keV; and (4) the model version 2...
March 14, 2018: Medical Physics
Robin De Roover, Wouter Crijns, Kenneth Poels, Ronald Peeters, Cédric Draulans, Karin Haustermans, Tom Depuydt
PURPOSE: Liquid fiducial markers have shown to be a promising alternative to solid gold markers in terms of imaging artifact reduction, patient comfort and compatibility with different imaging modalities. This study aims to investigate the performance of the novel BioXmark® liquid marker for state-of-the-art multi-modal imaging used in prostate cancer (PCa) radiotherapy, encompassing kV CT/CBCT, multi-parametric MRI and kV X-ray imaging. In addition, automatic detection of the liquid markers in X-ray imaging for prostate motion monitoring during treatment was investigated...
March 14, 2018: Medical Physics
Satomi Shiraishi, Michael P Grams, Luis E Fong de Los Santos
PURPOSE: To demonstrate an objective quality control framework for the image review process. METHODS AND MATERIALS: 927 cone-beam computed tomography (CBCT) registrations were retrospectively analyzed for 33 bilateral head and neck cancer patients who received definitive radiotherapy. Two registration tracking volumes (RTVs) - cervical spine (C-spine) and mandible - were defined, within which a similarity metric was calculated and used as a registration quality tracking metric over the course of treatment...
March 12, 2018: Medical Physics
Fatima Padilla-Cabal, Dietmar Georg, Hermann Fuchs
PURPOSE: The feasibility of Magnetic Resonance Image (MRI) based proton therapy is based, among several other factors, on the implementation of appropriate extensions on current dose calculation methods. This work aims to develop a pencil beam algorithm (PBA) for dose calculation of proton beams within magnetic field regions of up to 3T. METHODS: Monte Carlo (MC) simulations using the GATE 7.1/GEANT4.9.4p02 toolkit were performed to generate calibration and benchmarking data for the PBA...
March 12, 2018: Medical Physics
Yoshikazu Maeda, Yoshitaka Sato, Hiroki Minami, Yutaka Yasukawa, Kazutaka Yamamoto, Hiroyasu Tamamura, Satoshi Shibata, Sayuri Bou, Makoto Sasaki, Yuji Tameshige, Kyo Kume, Hiroshi Ooto, Shigeru Kasahara, Yasuhiro Shimizu, Yusuke Saga, Akira Omoya, Makoto Saitou
PURPOSE: To evaluate the effectiveness of CT image-guided proton radiotherapy for prostate cancer by analyzing the positioning uncertainty and assessing daily dose change due to anatomical variations. MATERIALS AND METHODS: Patients with prostate cancer were treated by opposed lateral proton beams based on a passive scattering method using an in-room CT image-guided system. The system employs a single couch for both CT scanning and beam delivery. The patient was positioned by matching the boundary between the prostate and the rectum's anterior region identified in the CT images to the corresponding boundary in the simulator images after bone matching...
March 12, 2018: Medical Physics
John W Hayes, Daniel Gomez-Cardona, Ran Zhang, Ke Li, Juan Pablo Cruz-Bastida, Guang-Hong Chen
PURPOSE: Low signal correction (LSC) in the raw counts domain has been shown to effectively reduce noise streaks in CT because the data inconsistency associated with photon-starved regions may be mitigated prior to the log transformation step. However, a systematic study of the performance of these raw data correction methods is still missing in literature. The purpose of this work was to provide such a systematic study for two well-known low signal correction schemes using either the adaptive trimmed mean (ATM) filter or the anisotropic diffusion (AD) filter in the raw counts domain...
March 12, 2018: Medical Physics
Daniel Gomez-Cardona, John Hayes, Ran Zhang, Ke Li, Juan Pablo Cruz-Bastida, Guang-Hong Chen
PURPOSE: Different low signal correction (LSC) methods have been shown to efficiently reduce noise streaks and noise level in CT to provide acceptable images at low radiation dose levels. These methods usually result in CT images with highly shift-variant and anisotropic spatial resolution and noise, which makes the parameter optimization process highly nontrivial. The purpose of this work was to develop a local task-based parameter optimization framework for LSC methods. METHODS: Two well-known LSC methods: the adaptive trimmed mean (ATM) filter and the anisotropic diffusion (AD) filter, were used as examples to demonstrate how to use the task-based framework to optimize filter parameter selection...
March 12, 2018: Medical Physics
Craig K Abbey, Frank W Samuelson, Rongping Zeng, John M Boone, Miguel P Eckstein, Kyle Myers
PURPOSE: This study investigates forced-localization of targets in simulated images with statistical properties similar to trans-axial sections of x-ray computed tomography (CT) volumes. A total of 24 imaging conditions are considered, comprising 2 target sizes, 3 levels of background variability, and 4 levels of frequency apodization. The goal of the study is to better understand how human observers perform forced-localization tasks in images with CT-like statistical properties. METHODS: The transfer properties of CT systems are modeled by a shift-invariant transfer function in addition to apodization filters that modulate high spatial frequencies...
March 12, 2018: Medical Physics
Jesse Tanguay, Ian A Cunningham
PURPOSE: Single-photon-counting (SPC) and spectroscopic x-ray detectors are under development in academic and industry laboratories for medical imaging applications. The spatial resolution of SPC and spectroscopic x-ray detectors is an important design criterion. The purpose of this article is to extend the cascaded systems approach to include a description of the spatial resolution of SPC and spectroscopic x-ray imaging detectors. METHODS: A cascaded systems approach was used to model reabsorption of characteristic x rays Coulomb repulsion, and diffusion in SPC and spectroscopic x-ray detectors...
March 11, 2018: Medical Physics
Qian Du, Chi Zhang, Xiaofeng Zhu, Xiaoying Liang, Chi Zhang, Vivek Verma, Kenneth Follet, Shuo Wang, Qiyong Fan, Rongtao Ma, Sumin Zhou, Dandan Zheng
OBJECTIVES: To apply advanced statistical and computational methodology in evaluating the impact of anatomical and technical variables on normal tissue dosimetry of trigeminal neuralgia (TN) stereotactic radiosurgery (SRS). METHODS: Forty patients treated with LINAC-based TN SRS with 90 Gy maximum dose were randomly selected for the study. Parameters extracted from the treatment plans for the study included three dosimetric output variables: the maximum dose to the brainstem (BSmax), the volume of brainstem that received at least 10 Gy (V10BS), and the volume of normal brain that received at least 12 Gy (V12)...
March 9, 2018: Medical Physics
Buxin Chen, Zheng Zhang, Dan Xia, Emil Y Sidky, Xiaochuan Pan
PURPOSE: We seek to investigate an optimization-based one-step method for image reconstruction that explicitly compensates for non-linear spectral response (i.e., the beam-hardening effect) in dual-energy CT, to investigate the feasibility of the one-step method for enabling two dual-energy partial-angular-scan configurations, referred to as the short- and half-scan configurations, on standard CT scanners without involving additional hardware, and to investigate the potential of the short- and half-scan configurations in reducing imaging dose and scan time in a single-kVp-switch full-scan configuration in which two full rotations are made for collection of dual-energy data...
March 8, 2018: Medical Physics
Adam Wang, Alexander Maslowski, Philippe Messmer, Mathias Lehmann, Adam Strzelecki, Elaine Yu, Pascal Paysan, Marcus Brehm, Peter Munro, Josh Star-Lack, Dieter Seghers
PURPOSE: To correct for scatter in kV cone-beam CT (CBCT) projection data on a clinical system using a new tool, Acuros® CTS, that estimates scatter images rapidly and accurately by deterministically solving the linear Boltzmann transport equation. METHODS: Phantom and patient CBCT scans were acquired on TrueBeam® radiotherapy machines. A first-pass reconstruction was used to create water and bone density maps of the imaged object, which was updated to include a more accurate representation of the patient couch...
March 6, 2018: Medical Physics
Alexander Maslowski, Adam Wang, Mingshan Sun, Todd Wareing, Ian Davis, Josh Star-Lack
PURPOSE: To describe Acuros® CTS, a new software tool for rapidly and accurately estimating scatter in x-ray projection images by deterministically solving the linear Boltzmann transport equation (LBTE). METHODS: The LBTE describes the behavior of particles as they interact with an object across spatial, energy, and directional (propagation) domains. Acuros CTS deterministically solves the LBTE by modeling photon transport associated with an x-ray projection in three main steps: 1) Ray tracing photons from the x-ray source into the object where they experience their first scattering event and form scattering sources...
March 6, 2018: Medical Physics
Ryosuke Ota, Ryoko Yamada, Takahiro Moriya, Tomoyuki Hasegawa
PURPOSE: Cherenkov radiation has recently received attention due to its prompt emission phenomenon, which has the potential to improve the timing performance of radiation detectors dedicated to positron emission tomography (PET). In this study, a Cherenkov based three-dimensional (3D) position sensitive radiation detector was proposed, which is composed of a monolithic lead fluoride (PbF2 ) crystal and a photodetector array of which the signals can be readout independently. METHODS: Monte Carlo simulations were performed to estimate the performance of the proposed detector...
March 6, 2018: Medical Physics
Yongqiang Tan, Lin Lu, Apurva Bonde, Deling Wang, Jing Qi, Lawrence H Schwartz, Binsheng Zhao
PURPOSE: Enlarged lymph nodes are indicators of cancer staging, and the change in their size is a reflection of treatment response. Automatic lymph node segmentation is challenging, as the boundary can be unclear and the surrounding structures complex. This work communicates a new three-dimensional algorithm for the segmentation of enlarged lymph nodes. METHODS: The algorithm requires a user to draw a region of interest (ROI) enclosing the lymph node. Rays are cast from the center of the ROI, and the intersections of the rays and the boundary of the lymph node form a triangle mesh...
March 3, 2018: Medical Physics
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