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Medical Physics

Erik Engwall, Albin Fredriksson, Lars Glimelius
PURPOSE: Interplay effects in proton radiotherapy can create large distortions in the dose distribution and severely degrade the plan quality. Standard methods to mitigate these effects include abdominal compression, gating and rescanning. We propose a new method to include the time structures of the delivery and organ motion in the framework of 4D robust optimization to generate plans that are robust against interplay effects. METHODS: The method considers multiple scenarios reflecting the uncertainties in the delivery and in the organ motion...
July 16, 2018: Medical Physics
M Saiful Huq, Min-Sig Hwang, Troy P Teo, Si Young Jang, Dwight E Heron, Ronald J Lalonde
PURPOSE: The International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) have jointly published a new code of practice (CoP), TRS483, for the dosimetry of small static photon fields used in external beam radiotherapy. It gave recommendations on how to perform reference dosimetry in non-standard machine-specific reference (msr) fields and measure field output factors in small fields. The purpose of this work was to perform a dosimetric evaluation of the recommendations given in this CoP...
July 15, 2018: Medical Physics
J B Farr, V Moskvin, R C Lukose, S Tuomanen, P Tsiamas, W Yao
PURPOSE: To invent, design, construct, and commission an intensity modulated minibeam proton therapy system (IMMPT) without the need for physical collimation and to compare its resulting conformity to a conventional IMPT system. METHODS: A proton therapy system (Hitachi, Ltd, Hitachi City, Japan; Model: Probeat-V) was specially modified to produce scanned minibeams without collimation. We performed Integral depth dose acquisitions and calibrations using a large-diameter parallel-plate ionization chamber in a scanning water phantom (PTW, Freiburg, Germany; Models: Bragg Peak ionization chamber, MP3-P)...
July 15, 2018: Medical Physics
Rachel B Ger, Jinzhong Yang, Yao Ding, Megan C Jacobsen, Carlos E Cardenas, Clifton D Fuller, Rebecca M Howell, Heng Li, R Jason Stafford, Shouhao Zhou, Laurence E Court
PURPOSE: Magnetic resonance imaging (MRI) provides non-invasive evaluation of patient's anatomy without using ionizing radiation. Due to this and the high soft-tissue contrast, MRI use has increased and has potential for use in longitudinal studies where changes in patients' anatomy or tumors at different time points are compared. Deformable image registration can be useful for these studies. Here we describe two data sets that can be used to evaluate the registration accuracy of systems for MR images, as it cannot be assumed to be the same as that measured on CT images...
July 14, 2018: Medical Physics
M Moteabbed, A Trofimov, F H Khan, Y Wang, G C Sharp, A L Zietman, J A Efstathiou, H-M Lu
PURPOSE: Hypofractionated radiotherapy of prostate cancer is gaining clinical acceptance given its potential increase in therapeutic ratio and evidence for noninferiority and lack of added late toxicities compared to conventional fractionation. However, concerns have been raised that smaller number of fractions might lead to larger dosimetric influence by interfractional motion. We aim to compare the effect of these variations on hypofractionated pencil beam scanning (PBS) proton therapy and volumetric modulated arc therapy (VMAT) for localized prostate cancer...
July 14, 2018: Medical Physics
Ken Sakaie, Xiaopeng Zhou, Jian Lin, Josef Debbins, Mark Lowe, Robert J Fox
PURPOSE: to determine if retrospective correction for noise floor effects can reduce systematic differences and improve reproducibility across major scanner changes. Changes in scanner configuration can negatively impact quantitative MRI studies by introducing systematic differences between measurements that are due to the instrument, not biology. Noise floor rectification is a potential source of systematic differences in diffusion tensor imaging (DTI). METHODS: Healthy volunteers were scanned before and after a major scanner change at four sites...
July 11, 2018: Medical Physics
Ehsan Samei, Todd Pawlicki, Daniel Bourland, Erika Chin, Shiva Das, Mary Fox, D Jay Freedma, Nicholas Hangiandreou, David Jordan, Melissa Martin, Robin Miller, William Pavlicek, Daniel Pavord, Lisa Schober, Bruce Thomadsen, Brendan Whelan
Derived from two years of deliberations and community engagement, Medical Physics 3.0 (MP3.0) is an effort commissioned by the American Association of Physicists in Medicine (AAPM) to devise a framework of strategies by which medical physicists can maintain and improve their integral roles in, and contributions to, healthcare and its innovation under conditions of rapid change and uncertainty. Towards that goal, MP3.0 advocates a broadened and refreshed model of sustainable excellence by which medical physicists can and should contribute to healthcare...
July 10, 2018: Medical Physics
Michael K Fix, Daniel Frei, Werner Volken, Dario Terribilini, Silvan Mueller, Olgun Elicin, Hossein Hemmatazad, Daniel M Aebersold, Peter Manser
PURPOSE: Even though volumetric modulated arc therapy (VMAT) is a well-accepted treatment technique in radiotherapy using a coplanar delivery approach, VMAT might be further improved by including dynamic table and collimator rotations leading to dynamic trajectory radiotherapy (DTRT). In this work an optimization procedure for DTRT was developed and the potential benefit of DTRT was investigated for different treatment sites. METHODS: For this purpose, a dedicated optimization framework for DTRT was developed using the Eclipse Scripting Research Application Programming Interface (ESRAPI)...
July 10, 2018: Medical Physics
S Mueller, P Manser, W Volken, D Frei, R Kueng, E Herrmann, O Elicin, D M Aebersold, M F M Stampanoni, M K Fix
PURPOSE: To develop a treatment technique for dynamic mixed beam radiotherapy (DYMBER) utilizing increased degrees of freedom (DoF) of a conventional treatment unit including different particle types (photons and electrons), intensity and energy modulation and dynamic gantry, table and collimator rotations. METHODS: A treatment planning process has been developed to create DYMBER plans combining photon dynamic trajectories (DTs) and step and shoot electron apertures collimated with the photon multileaf collimator (pMLC)...
July 10, 2018: Medical Physics
I D Muñoz, I Gamboa-deBuen, O Avila, M E Brandan
PURPOSE: To evaluate the photon field effective energy (Eeff ) distribution and percentage depth dose (PDD) within a mammography phantom by analysis of the CaF2 :Tm (TLD-300) thermoluminescent (TL) glow curve. The experimental procedure involves the use of TLD-300 to determine with single dosimeter exposures both the relative dose and the beam quality. METHODS: TLD-300 chips were exposed to X-rays from a GE Senographe 2000D mammography unit at the surface and different depths within a BR12 phantom...
July 10, 2018: Medical Physics
Hoda Nemat, Hamid Fehri, Nasrin Ahmadinejad, Alejandro F Frangi, Ali Gooya
PURPOSE: This work proposes a new reliable Computer Aided Diagnostic (CAD) system for the diagnosis of breast cancer from Breast Ultrasound (BUS) images. The system can be useful to reduce the number of biopsies and pathological tests, which are invasive, costly, and often unnecessary. METHODS: The proposed CAD system classifies breast tumors into benign and malignant classes using morphological and textural features extracted from Breast Ultrasound (BUS) images...
July 5, 2018: Medical Physics
Günther H Hartmann, Klemens Zink
PURPOSE: The dose conversion factor plays an important role in the dosimetry by enabling the absorbed dose in the sensitive volume of a detector to be converted into the absorbed dose in the surrounding medium (in most cases water). The purpose of this paper is to demonstrate that a specific fluence based approach for the decomposition of the dose conversion factor is in particular useful for the interpretation of the influences of detector properties on measurements under non-reference conditions...
July 5, 2018: Medical Physics
George Noid, An Tai, Diane Schott, Nilesh Mistry, Yu Liu, Taly Gilat Schmidt, Jared Robbins, X Allen Li
PURPOSE: The purpose of this work is to investigate the use of low-energy monoenergetic decompositions obtained from dual energy CT (DECT) to enhance image contrast and the detection of radiation-induced changes of CT textures in pancreatic cancer. METHODS: DECT data acquired for 10 consecutive pancreatic cancer patients during routine non-gated CT-guided radiation therapy (RT) using an in-room CT (Definition AS Open, Siemens Healthcare, Malvern, PA) were analyzed...
July 4, 2018: Medical Physics
Gal Mazor, Lior Weizman, Assaf Tal, Yonina C Eldar
PURPOSE: Magnetic Resonance Fingerprinting (MRF) is a relatively new approach that provides quantitative MRI measures using randomized acquisition. Extraction of physical quantitative tissue parameters is performed off-line, without the need of patient presence, based on acquisition with varying parameters and a dictionary generated according to the Bloch equation simulations. MRF uses hundreds of radio frequency (RF) excitation pulses for acquisition, and therefore a high undersampling ratio in the sampling domain (k-space) is required for reasonable scanning time...
July 4, 2018: Medical Physics
Claudia Mendez, Nadine Colpo, Cheryl Duzenli, Parmveer Atwal, Brad Gill
PURPOSE: This work aims to evaluate the utility and accuracy of a mouse-like phantom and optically stimulated luminescent dosimeters (OSLDs) in measuring dose delivered to the body and lung of mice undergoing micro-CT imaging. METHODS: A phantom with two cavities for NanoDot OSLDs (Landauer, Inc., Greenwood, IL) was designed and constructed using acrylic to model the mouse body and polyurethane foam to obtain an approximate lung tissue dose. The OSLD dose was compared to ion chamber measurements for the same imaging protocols delivered by a Siemens Inveon micro-CT (Siemens Medical Solutions USA, Inc)...
July 3, 2018: Medical Physics
Zepa Yang, Hyeongmin Jin, Jong Hyo Kim
PURPOSE: The dimensions of small airways with an internal diameter of less than 2-3 mm are important biomarkers for the evaluation of pulmonary diseases, such as asthma and chronic obstructive pulmonary disease (COPD). The resolution limitations of CT systems, however, have remained a barrier to be of use for determining the small airway dimensions. We present a novel approach, called the attenuation profile matching (APM) method, which allows for the accurate determination of the small airway dimension while being robust to varying CT scan parameters...
July 3, 2018: Medical Physics
Gengsheng L Zeng
PURPOSE: In emission tomography, the EM (expectation maximization) algorithm is easy to use with only one parameter to adjust - the number of iterations. On the other hand, the EM algorithms for transmission tomography are not so user-friendly and have many problems. This paper develops a new transmission algorithm similar to the emission EM algorithm. METHODS: This paper develops a family of emission-EM-look-alike algorithms by expressing the emission EM algorithm in the additive form and changing the weighting factor...
July 2, 2018: Medical Physics
Kuang Ming-Xing, Kuang Shi-Jiang, Xiao Qiu-Jin, Kuang Nan-Zhen, Zhao Hui, Cheng Xiao-Ling
PURPOSE: The aim of this study is to explore a calculated method used to measure the cardiac output using the aortic impedance change component of reconstructed impedance cardiography. METHODS: Routine impedance cardiography was measured using Kubicek's method with four ring electrodes. The thoracic mixed impedance changes were measured by six leads, which consisted of 15 electrodes. The aortic impedance change component was separated from six thoracic mixed impedance changes through waveform reconstruction...
July 2, 2018: Medical Physics
Chenhui Liu, Yufeng Zhou
PURPOSE: High-intensity focused ultrasound (HIFU) is becoming an effective and noninvasive treatment modality for cancer and solid tumors. In order to avoid the cancer relapse and guarantee the success of ablation, there should be no gaps left among all HIFU-generated lesions. However, there are few imaging approaches available for detecting the HIFU lesion gaps in real time during ablation. METHODS: Transient axial shear strain elastograms (ASSEs) were proposed and evaluated both numerically and experimentally to detect the lesion gaps immediately after the cessation of therapeutic HIFU exposure...
July 2, 2018: Medical Physics
Arman Sarfehnia, Mark Ruschin, Brige Chugh, Collins Yeboah, Nathan Becker, Young-Bin Cho, Young Lee
PURPOSE: This work describes the performance characterization of a cone-beam CT guided radiosurgery device, the Gamma Knife® Icon™ . METHODS: The performance tests have been categorized into: 1) Image quality and mechanical integrity; 2) Image co-registration fidelity; 3) Adaptive treatment delivery quality; 4) High definition motion management performance characterization; 5) Software communication performance testing of the integrated cone-beam CT (CBCT) system...
June 29, 2018: Medical Physics
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