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Physics in Medicine and Biology

Sébastien Brousmiche, Kevin Souris, Jonathan Orban de Xivry, John Aldo Lee, Benoit Macq, Joao Seco
Proton range random and systematic uncertainties are the major factors undermining the advantages of proton therapy, namely, a sharp dose falloff and a better dose conformality for lower doses in normal tissues. The influence of CT artifacts such as beam hardening or scatter can easily be understood and estimated due to their large-scale effects on the CT image, like cupping and streaks. In comparison, the effects of weakly-correlated stochastic noise are more insidious and less attention is drawn on them partly due to the common belief that they only contribute to proton range uncertainties and not to systematic errors thanks to some averaging effects...
August 17, 2017: Physics in Medicine and Biology
Natalia Kostiukhina, Dietmar Georg, Sofia Rollet, Peter Kuess, Andrej Sipaj, Piotr Andrzejewski, Hugo Furtado, Ivo Rausch, Wolfgang Lechner, Elisabeth Steiner, Hunor Kertesz, Barbara Knaeusl
A novel breathing phantom was designed for being used in conventional and ion-beam radiotherapy as well as for medical imaging. Accurate dose delivery and patient safety are aimed to be verified for four-dimensional (4D) treatment techniques compensating for breathing-induced tumor motion. The phantom includes anthropomorphic components representing an average human thorax. It consists of real tissue equivalent materials to fulfill the requirements for dosimetric experiments and imaging purposes. The different parts of the torso (lungs, chest wall, and ribs) and the tumor can move independently...
August 17, 2017: Physics in Medicine and Biology
Mark Ostyn, Thomas Dwyer, Matthew Miller, Paden King, Rachel Sacks, Ross Cruikshank, Melvin Rosario, Daniel Martinez, Siyong Kim, Woon-Hong Yeo
In cancer treatment with radiation, accurate patient setup is critical for proper dose delivery. Improper arrangement can lead to disease recurrence, permanent organ damage, or lack of disease control. While current immobilization equipment often helps for patient positioning, manual adjustment is required, involving iterative, time-consuming steps. Here, we present an electromechanical robotic system for improving patient setup in radiotherapy, specifically targeting head and neck cancer. This positioning system offers six degrees of freedom for a variety of applications in radiation oncology...
August 17, 2017: Physics in Medicine and Biology
Wook-Geun Shin, Mauro Testa, Hak Soo Kim, Jong Hwi Jeong, Se Byeong Lee, Yeon-Joo Kim, Chul Hee Min
For the independent validation of treatment plans, we developed a Monte Carlo (MC)-based patient dose calculation system with the tool for particle simulation (TOPAS) to enable routine and automatic dose recalculation for each patient. The proton beam nozzle was modeled with TOPAS to simulate the therapeutic beam, and MC commissioning was performed by comparing percent depth dose with the measurement. The beam set-up based on the prescribed beam range and modulation width was automated by modifying the vendor-specific method...
August 15, 2017: Physics in Medicine and Biology
Mohammad Nakhostin
Despite several attractive properties, the poor timing performance of compound semiconductor detectors such as CdTe and CdZnTe has hindered their use in commercial PET imaging systems. The standard method of pulse timing with such detectors is to employ a constant-fraction discriminator (CFD) at the output of a timing filter which is fed by the pulses from a charge-sensitive preamplifier. The method has led to a time resolution of about 10 ns at full-width at half-maximum (FWHM) with 1 mm thick CdTe detectors...
August 15, 2017: Physics in Medicine and Biology
Theresa Ida Götz, Godehard Lahmer, Tobias Brandt, Karoline Kallis, Vratislav Strnad, Christoph Bert, Bernhard Hensel, Ana Maria Tome, Elmar W Lang
Modern radiotherapy of female breat cancers often employ high dose rate Brachytherapy, where a radioactive source is moved inside catheters, implanted in the female breast, according to a prescribed treatment plan. Source localization relative to the patient's anatomy is determined with solenoid sensors whose spatial positions are measured with an electromagnetic tracking system. Precise sensor dwell position determination is of utmost importance to assure irradiation of the cancerous tissue according to the treatment plan...
August 10, 2017: Physics in Medicine and Biology
Marie de Saint Victor, Dario Carugo, Lester C Barnsley, Joshua Owen, Constantin C Coussios, Eleanor Stride
Ultrasound and microbubbles have been shown to accelerate the breakdown of blood clots both in vitro and in vivo. Clinical translation of this technology is still limited, however, in part by inefficient microbubble delivery to the thrombus. This study examines the obstacles to delivery posed by fluid dynamic conditions in occluded vasculature and investigates whether magnetic targeting can improve microbubble delivery. A two-dimensional computational fluid dynamic (CFD) model of a fully occluded Y-shaped microarterial bifurcation was developed to determine: (i) the fluid dynamic field in the vessel with inlet velocities from 1-100mm/s (corresponding to Reynolds numbers 0...
August 10, 2017: Physics in Medicine and Biology
Emmanouil Zoros, Argyris S Moutsatsos, Eleftherios P Pappas, Evangelos Georgiou, Georgios Kollias, Pantelis Karaiskos, Evaggelos Pantelis
Detector-, field size- and machine-specific correction factors are required for precise dosimetry measurements in small and non-standard photon fields. In this work, Monte Carlo (MC) simulation techniques were used to calculate the correction factors for a series of ionization chambers, a synthetic microDiamond and diode dosimeters, used for reference and/or output factor (OF) measurements in the Gamma Knife Perfexion photon fields. Calculations were performed for the Solid Water (SW) and ABS plastic phantoms, as well as for a water phantom of the same geometry...
August 10, 2017: Physics in Medicine and Biology
Dianning He, Marta A Zamora, Aytekin Oto, Gregory S Karczmar, Xiaobing Fan
Differences between region-of-interest (ROI) and pixel-by-pixel analysis of dynamic contrast enhanced (DCE) MRI data were investigated in this study with computer simulations and pre-clinical experiments. ROIs were simulated with 10, 50, 100, 200, 400, and 800 different pixels. For each pixel, a contrast agent concentration as a function of time, C(t), was calculated using the Tofts DCE-MRI model with randomly generated physiological parameters (Ktrans and ve) and the Parker population arterial input function...
August 8, 2017: Physics in Medicine and Biology
Marthony Robins, Justin Bennion Solomon, Pooyan Sahbaee, Martin Sedlmair, Kingshuk Roy Choudhury, Aria Pezeshk, Berkman Sahiner, Ehsan Samei
The purpose of this study was to assess three methods (an established and two newly developed techniques) for inserting virtual lung nodules into CT images. Assessment was done by comparing virtually inserted nodules to physical nodules with respect to nodule volume and shape. Methods: 24 synthetic nodules (three sizes, four morphologies) were physically inserted into the lung cavity of an anthropomorphic chest phantom (KYOTO KAGAKU). The phantom was imaged with and without nodules on a commercial CT scanner (SOMATOM Definition Flash, Siemens) using standard thoracic CT protocols at two dose levels (1...
August 8, 2017: Physics in Medicine and Biology
Christopher N Acconcia, Ryan Matthew Jones, David E Goertz, Meaghan Anne O'Reilly, Kullervo Hynynen
It is well established that high intensity focused ultrasound can be used to disintegrate clots. This approach has the potential to rapidly and noninvasively resolve clot causing occlusions in cardiovascular diseases such as deep vein thrombosis (DVT). However, lack of an appropriate treatment monitoring tool is currently a limiting factor in its widespread adoption. Here we conduct cavitation imaging with a large aperture, sparse hemispherical receiver array during sonothrombolysis with multi-cycle burst exposures (0...
August 8, 2017: Physics in Medicine and Biology
Luis Isaac Ramos Garcia, Jose Fernando Perez Azorin, Pedro-Borja Aguilar-Redondo, Veronica Moran-Velasco
In this study we present a new procedure for the comparison of two dose matrices by means of a statistical test. A statistical distance is proposed to decide whether the difference between the two matrices is statistically significant. This statistical test is based on the square difference between the experimental and expected gamma matrix results. The expected gamma matrix is calculated by simulating the measurement process. The criteria for significance is chosen to give the same α-type error as the usual gamma-pass rate criteria, i...
August 8, 2017: Physics in Medicine and Biology
Kyle Joseph Gallagher, Jennifer Wong, Junan Zhang
The purpose of this study was to demonstrate the feasibility of using a commercial two-dimensional (2D) detector array with an inherent detector spacing of 5 mm to achieve submillimeter accuracy in localizing the radiation isocenter. This was accomplished by delivering the Vernier "dose" caliper to a 2D detector array where the nominal scale was the 2D detector array and the non-nominal Vernier scale was the radiation dose strips produced by the high-definition (HD) multileaf collimators (MLCs) of the linear accelerator...
August 7, 2017: Physics in Medicine and Biology
Yinliang Diao, Weinong Sun, Yaqing He, Saiwing Leung, Yun Ming Siu
In this paper, a novel source model based on magnetic vector potential for assessment of the induced electric field strength in human body exposed to low-frequency (LF) magnetic field of an electrical appliance is presented. The construction of the vector potential model requires only a single-component magnetic field to be measured close to the appliance under test, hence relieving a lot of practical measurement effort - the radial basis functions (RBFs) are adopted for the interpolation of discrete measurements; the magnetic vector potential model can then be directly constructed by summing a set of simple algebraic functions of RBF parameters...
August 7, 2017: Physics in Medicine and Biology
Niki Martini, Vaia Koukou, George Fountos, Christos Michail, Athanasios Bakas, Ioannis S Kandarakis, Robert David Speller, George C Nikiforidis
Calcifications are products of mineralization whose presence is usually associated with pathological conditions. The minerals mostly seen in several diseases are calcium oxalate (CaC2O4), calcium carbonate (CaCO3) and hydroxyapatite (HAp). Up to date, there is no in-vivo method that could discriminate between minerals. To this aim, a dual energy X-ray method was developed in the present study. An analytical model was implemented for the determination of the Calcium/Phosphorus mass ratio (mca/mp ). The simulation was carried out using monoenergetic and polyenergetic X-rays and various calcification thicknesses (100 to 1000 um) and types (CaC2O4, CaCO3, HAp)...
August 4, 2017: Physics in Medicine and Biology
Steven P Kearney, Shreyan Majumdar, Thomas J Royston, Dieter Klatt
The feasibility of sample interval modulation (SLIM) magnetic resonance elastography (MRE) for the in vivo mouse brain is assessed, and an alternative SLIM-MRE encoding method is introduced. In SLIM-MRE, the phase accumulation for each motion direction is encoded simultaneously by varying either the start time of the motion encoding gradient (MEG), SLIM-phase constant (SLIM-PC), or the initial phase of the MEG, SLIM-phase varying (SLIM-PV). SLIM-PC provides gradient moment nulling, but the mutual gradient shift necessitates increased echo time (TE)...
August 4, 2017: Physics in Medicine and Biology
Bjorn Stemkens, Markus Glitzner, Charis Kontaxis, Baudouin Denis de Senneville, Fieke M Prins, Sjoerd P M Crijns, Linda G W Kerkmeijer, Jan J W Lagendijk, Cornelis A T Van den Berg, Rob H N Tijssen
Stereotactic body radiation therapy (SBRT) has shown great promise in increasing local control rates for renal-cell carcinoma (RCC). Characterized by steep dose gradients and high fraction doses, these hypo-fractionated treatments are, however, prone to dosimetric errors as a result of variations in intra-fraction respiratory-induced motion, such as drifts and amplitude alterations. This may lead to significant variations in the deposited dose. This study aims to develop a method for calculating the accumulated dose for MRI-guided SBRT of RCC in the presence of intra-fraction respiratory variations and determine the effect of such variations on the deposited dose...
August 3, 2017: Physics in Medicine and Biology
Wolfgang Lechner, Peter Kuess, Dietmar Georg, Hugo Palmans
Various types of treatment units such as CyberKnife, TomoTherapy and C-arm linear accelerators (LINACs) are operated using flattening filter free (FFF) photon beams. Their reference dosimetry, however, is currently based on codes of practice that provide data which were primarily developed and tested for high-energy photon beams with flattering filter (WFF). The aim of this work was to introduce equivalent uniform square field sizes of FFF beams to serve as a basis of a unified reference dosimetry procedure applicable to all aforementioned FFF machines...
August 3, 2017: Physics in Medicine and Biology
Kevin J Parker
Elastography of the brain is a topic of clinical and preclinical research, motivated by the potential for viscoelastic measures of the brain to provide sensitive indicators of pathological processes, and to assist in early diagnosis. To date, studies of the normal brain and of those with confirmed neurological disorders have reported a wide range of shear stiffness and shear wave speeds, even within similar categories. A range of factors including the shear wave frequency, and the age of the individual are thought to have a possible influence...
August 2, 2017: Physics in Medicine and Biology
Koen Salvo, Michel Defrise
The 'simultaneous Maximum-Likelihood Attenuation Correction Factors' (sMLACF) algorithm presented here, is an iterative algorithm to calculate the maximum-likelihood (ML) estimate of the activity 'λ' and the attenuation factors 'a' in time-of-flight (TOF) positron emission tomography (PET), and this from emission data only. Hence sMLACF is an alternative to the MLACF algorithm. sMLACF is derived using the generalized expectation-maximization (GEM) principle by introducing an appropriate set of complete data...
July 28, 2017: Physics in Medicine and Biology
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