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Physics in Medicine and Biology

B Koger, C Kirkby
As a recent area of development in radiation therapy, gold nanoparticle (GNP) enhanced radiation therapy has shown potential to increase tumour dose while maintaining acceptable levels of healthy tissue toxicity. In this study, the effect of varying photon beam energy in GNP enhanced arc radiation therapy (GEART) is quantified through the introduction of a dose scoring metric, and GEART is compared to a conventional radiotherapy treatment. The PENELOPE Monte Carlo code was used to model several simple phantoms consisting of a spherical tumour containing GNPs (concentration: 15 mg Au g(-1) tumour, 0...
December 2, 2016: Physics in Medicine and Biology
S Dowdell, M Tyler, J McNamara, K Sloan, A Ceylan, A Rinks
Plane-parallel ionisation chambers are regularly used to conduct relative dosimetry measurements for therapeutic kilovoltage beams during commissioning and routine quality assurance. This paper presents the first quantification of the polarity effect in kilovoltage photon beams for two types of commercially available plane-parallel ionisation chambers used for such measurements. Measurements were performed at various depths along the central axis in a solid water phantom and for different field sizes at 2 cm depth to determine the polarity effect for PTW Advanced Markus and Roos ionisation chambers (PTW-Freiburg, Germany)...
November 15, 2016: Physics in Medicine and Biology
Sumin Zhou, Xiaofeng Zhu, Mutian Zhang, Dandan Zheng, Yu Lei, Sicong Li, Nathan Bennion, Vivek Verma, Weining Zhen, Charles Enke
In the delivery of non-gated radiotherapy (RT), owing to intra-fraction organ motion, a certain degree of RT dose uncertainty is present. Herein, we propose a novel mathematical algorithm to estimate the mean and variance of RT dose that is delivered without gating. These parameters are specific to individual internal organ motion, dependent on individual treatment plans, and relevant to the RT delivery process. This algorithm uses images from a patient's 4D simulation study to model the actual patient internal organ motion during RT delivery...
November 2, 2016: Physics in Medicine and Biology
B Bassey, M Martinson, N Samadi, G Belev, C Karanfil, P Qi, D Chapman
A multiple energy imaging system that can extract multiple endogenous or induced contrast materials as well as water and bone images would be ideal for imaging of biological subjects. The continuous spectrum available from synchrotron light facilities provides a nearly perfect source for multiple energy x-ray imaging. A novel multiple energy x-ray imaging system, which prepares a horizontally focused polychromatic x-ray beam, has been developed at the BioMedical Imaging and Therapy bend magnet beamline at the Canadian Light Source...
November 2, 2016: Physics in Medicine and Biology
Marc J P Chamberland, Randle E P Taylor, D W O Rogers, Rowan M Thomson
egs_brachy is a versatile and fast Monte Carlo (MC) code for brachytherapy applications. It is based on the EGSnrc code system, enabling simulation of photons and electrons. Complex geometries are modelled using the EGSnrc C++ class library and egs_brachy includes a library of geometry models for many brachytherapy sources, in addition to eye plaques and applicators. Several simulation efficiency enhancing features are implemented in the code. egs_brachy is benchmarked by comparing TG-43 source parameters of three source models to previously published values...
November 2, 2016: Physics in Medicine and Biology
X Hou, J Tanguay, M Vuckovic, K Buckley, P Schaffer, F Bénard, T J Ruth, A Celler
Cyclotron-produced (99m)Tc (CPTc) has been recognized as an attractive and practical substitution of reactor/generator based (99m)Tc. However, the small amount of (92-98)Mo in the irradiation of enriched (100)Mo could lead to the production of other radioactive technetium isotopes (Tc-impurities) which cannot be chemically separated. Thus, these impurities could contribute to patient dose and affect image quality. The potential radiation dose caused by these Tc-impurities produced using different targets, irradiation conditions, and corresponding to different injection times have been investigated, leading us to create dose-based limits of these parameters for producing clinically acceptable CPTc...
November 2, 2016: Physics in Medicine and Biology
Michael Jermyn, Joannie Desroches, Kelly Aubertin, Karl St-Arnaud, Wendy-Julie Madore, Etienne De Montigny, Marie-Christine Guiot, Dominique Trudel, Brian C Wilson, Kevin Petrecca, Frederic Leblond
There is an urgent need for improved techniques for disease detection. Optical spectroscopy and imaging technologies have potential for non- or minimally-invasive use in a wide range of clinical applications. The focus here, in vivo Raman spectroscopy (RS), measures inelastic light scattering based on interaction with the vibrational and rotational modes of common molecular bonds in cells and tissue. The Raman 'signature' can be used to assess physiological status and can also be altered by disease. This information can supplement existing diagnostic (e...
December 7, 2016: Physics in Medicine and Biology
C Grassberger, H Paganetti
The variety of treatment options for cancer patients has increased significantly in recent years. Not only do we combine radiation with surgery and chemotherapy, new therapeutic approaches such as immunotherapy and targeted therapies are starting to play a bigger role. Physics has made significant contributions to radiation therapy treatment planning and delivery. In particular, treatment plan optimization using inverse planning techniques has improved dose conformity considerably. Furthermore, medical physics is often the driving force behind tumor control and normal tissue complication modeling...
October 19, 2016: Physics in Medicine and Biology
Andreas A Schoenfeld, Soeren Wieker, Dietrich Harder, Bjoern Poppe
The optical origin of the lateral response and orientation artifacts, which occur when using EBT3 and EBT-XD radiochromic films together with flatbed scanners, has been reinvestigated by experimental and theoretical means. The common feature of these artifacts is the well-known parabolic increase in the optical density OD(x)  =  -log10 I(x)/I 0(x) versus offset x from the scanner midline (Poppinga et al 2014 Med. Phys. 41 021707). This holds for landscape and portrait orientations as well as for the three color channels...
October 14, 2016: Physics in Medicine and Biology
Daniel Sanchez-Parcerisa, Maura Kirk, Marcus Fager, Brendan Burgdorf, Malorie Stowe, Tim Solberg, Alejandro Carabe
The development of rotational proton therapy plans based on a pencil-beam-scanning (PBS) system has been limited, among several other factors, by the energy-switching time between layers, a system-dependent parameter that ranges between a fraction of a second and several seconds. We are investigating mono- and bi-energetic rotational proton modulated arc therapy (PMAT) solutions that would not be affected by long energy switching times. In this context, a systematic selection of the optimal proton energy for each arc is vital...
October 14, 2016: Physics in Medicine and Biology
A Lourenço, N Wellock, R Thomas, M Homer, H Bouchard, T Kanai, N MacDougall, G Royle, H Palmans
Water-equivalent plastics are frequently used in dosimetry for experimental simplicity. This work evaluates the water-equivalence of novel water-equivalent plastics specifically designed for light-ion beams, as well as commercially available plastics in a clinical high-energy carbon-ion beam. A plastic- to-water conversion factor [Formula: see text] was established to derive absorbed dose to water in a water phantom from ionization chamber readings performed in a plastic phantom. Three trial plastic materials with varying atomic compositions were produced and experimentally characterized in a high-energy carbon-ion beam...
October 14, 2016: Physics in Medicine and Biology
Alexandra Zvereva, Nina Petoussi-Henss, Wei Bo Li, Helmut Schlattl, Uwe Oeh, Maria Zankl, Frank Philipp Graner, Christoph Hoeschen, Stephan G Nekolla, Katia Parodi, Markus Schwaiger
The objective of this work was to investigate the influence of the definition of blood as a distinct source on organ doses, associated with the administration of a novel radiopharmaceutical for positron emission tomography-computed tomography (PET/CT) imaging-(S)-4-(3-(18)F-fluoropropyl)-L-glutamic acid ((18)F-FSPG). Personalised pharmacokinetic models were constructed based on clinical PET/CT images from five healthy volunteers and blood samples from four of them. Following an identifiability analysis of the developed compartmental models, person-specific model parameters were estimated using the commercial program SAAM II...
October 14, 2016: Physics in Medicine and Biology
K M Ratheesh, L K Seah, V M Murukeshan
The automatic calibration in Fourier-domain optical coherence tomography (FD-OCT) systems allows for high resolution imaging with precise depth ranging functionality in many complex imaging scenarios, such as microsurgery. However, the accuracy and speed of the existing automatic schemes are limited due to the functional approximations and iterative operations used in their procedures. In this paper, we present a new real-time automatic calibration scheme for swept source-based optical coherence tomography (SS-OCT) systems...
October 14, 2016: Physics in Medicine and Biology
Brent F B Huisman, J M Létang, É Testa, D Sarrut
There is interest in the particle therapy community in using prompt gammas (PGs), a natural byproduct of particle treatment, for range verification and eventually dose control. However, PG production is a rare process and therefore estimation of PGs exiting a patient during a proton treatment plan executed by a Monte Carlo (MC) simulation converges slowly. Recently, different approaches to accelerating the estimation of PG yield have been presented. Sterpin et al (2015 Phys. Med. Biol. 60 4915-46) described a fast analytic method, which is still sensitive to heterogeneities...
October 14, 2016: Physics in Medicine and Biology
C L Campbell, C T A Brown, K Wood, H Moseley
Most existing theoretical models of photodynamic therapy (PDT) assume a uniform initial distribution of the photosensitive molecule, Protoporphyrin IX (PpIX). This is an adequate assumption when the prodrug is systematically administered; however for topical PDT this is no longer a valid assumption. Topical application and subsequent diffusion of the prodrug results in an inhomogeneous distribution of PpIX, especially after short incubation times, prior to light illumination. In this work a theoretical simulation of PDT where the PpIX distribution depends on the incubation time and the treatment modality is described...
October 7, 2016: Physics in Medicine and Biology
N De Geeter, P Lioumis, A Laakso, G Crevecoeur, L Dupré
When delivered over a specific cortical site, TMS can temporarily disrupt the ongoing process in that area. This allows mapping of speech-related areas for preoperative evaluation purposes. We numerically explore the observed variability of TMS responses during a speech mapping experiment performed with a neuronavigation system. We selected four cases with very small perturbations in coil position and orientation. In one case (E) a naming error occurred, while in the other cases (NEA, B, C) the subject appointed the images as smoothly as without TMS...
October 7, 2016: Physics in Medicine and Biology
Wonmo Sung, Seongmoon Jung, Sung-Joon Ye
The aim of this study is to investigate the dosimetric characteristics of nanoparticle-enhanced Auger therapy. Monte Carlo (MC) simulations were performed to assess electron energy spectra and dose enhancement distributions around a nanoparticle. In the simulations, two types of nanoparticle structures were considered: nanoshell and nanosphere, both of which were assumed to be made of one of five elements (Fe, Ag, Gd, Au, and Pt) in various sizes (2-100 nm). Auger-electron emitting radionuclides (I-125, In-111, and Tc-99m) were simulated within a nanoshell or on the surface of a nanosphere...
October 7, 2016: Physics in Medicine and Biology
C S Moore, T J Wood, G Avery, S Balcam, L Needler, H Joshi, J R Saunderson, A W Beavis
The use of three physical image quality metrics, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and mean effective noise equivalent quanta (eNEQm) have recently been examined by our group for their appropriateness in the calibration of an automatic exposure control (AEC) device for chest radiography with an Agfa computed radiography (CR) imaging system. This study uses the same methodology but investigates AEC calibration for abdomen, pelvis and spine CR imaging. AEC calibration curves were derived using a simple uniform phantom (equivalent to 20 cm water) to ensure each metric was held constant across the tube voltage range...
October 7, 2016: Physics in Medicine and Biology
C Bopp, R Hirayama, T Inaniwa, A Kitagawa, N Matsufuji, K Noda
Ion beams present a potential advantage in terms of treatment of lesions with hypoxic regions. In order to use this potential, it is important to accurately model the cell survival of oxic as well as hypoxic cells. In this work, an adaptation of the microdosimetric kinetic (MK) model making it possible to account for cell hypoxia is presented. The adaptation relies on the modification of damage quantity (double strand breaks and more complex lesions) due to the radiation. Model parameters such as domain size and nucleus size are then adapted through a fitting procedure...
October 7, 2016: Physics in Medicine and Biology
Simon R Cherry, Maggie Simmons
No abstract text is available yet for this article.
October 7, 2016: Physics in Medicine and Biology
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