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https://www.readbyqxmd.com/read/28220403/dosimetry-in-mars-spectral-ct-topas-monte-carlo-simulations-and-ion-chamber-measurements
#1
Gray Lu, Steven Marsh, Jerome Damet, Pierre Carbonez, John Laban, Christopher Bateman, Anthony Butler, Phil Butler
Spectral computed tomography (CT) is an up and coming imaging modality which shows great promise in revealing unique diagnostic information. Because this imaging modality is based on X-ray CT, it is of utmost importance to study the radiation dose aspects of its use. This study reports on the implementation and evaluation of a Monte Carlo simulation tool using TOPAS for estimating dose in a pre-clinical spectral CT scanner known as the MARS scanner. Simulated estimates were compared with measurements from an ionization chamber...
February 20, 2017: Australasian Physical & Engineering Sciences in Medicine
https://www.readbyqxmd.com/read/28214683/neutron-measurements-in-radiotherapy-a-method-to-correct-neutron-sensitive-devices-for-parasitic-photon-response
#2
L Irazola, J A Terrón, R Bedogni, A Pola, M Lorenzoli, E Jimenez-Ortega, A R Barbeiro, B Sánchez-Nieto, F Sánchez-Doblado
One of the major causes of secondary malignancies after radiotherapy treatments are peripheral doses, known to increase for some newer techniques (such as IMRT or VMAT). For accelerators operating above 10MV, neutrons can represent important contribution to peripheral doses. This neutron contamination can be measured using different passive or active techniques, available in the literature. As far as active (or direct-reading) procedures are concerned, a major issue is represented by their parasitic photon sensitivity, which can significantly affect the measurement when the point of test is located near to the field-edge...
February 12, 2017: Applied Radiation and Isotopes
https://www.readbyqxmd.com/read/28212111/direct-determination-of-k-q-for-farmer-type-ionization-chambers-in-a-clinical-scanned-carbon-ion-beam-using-water-calorimetry
#3
J-M Osinga-Blättermann, S Brons, S Greilich, O Jäkel, A Krauss
Until now, the dosimetry of carbon ions with ionization chambers has not reached the same level of accuracy as that of high-energy photons. This is mainly caused by the approximately threefold larger uncertainty of the k Q factor of ionization chambers, which, due to the lack of experimental data, is still derived by calculations. Measurements of absorbed dose to water, D w, by means of water calorimetry have now been performed in the entrance channel of a scanned 6 cm  ×  6 cm radiation field of 429 MeV/u carbon ions, allowing the direct calibration of ionization chambers and thus the experimental determination of k Q...
February 17, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28211796/fluence-correction-factor-for-graphite-calorimetry-in-a-clinical-high-energy-carbon-ion-beam
#4
Ana Lourenco, Russell Thomas, Michael Homer, Hugo Bouchard, Severine Rossomme, James Renaud, Tatsuaki Kanai, Gary Royle, Hugo Palmans
The aim of this work is to develop and adapt a formalism to determine absorbed dose to water from graphite calorimetry measurements in carbon-ion beams. Fluence correction factors, <i>k</i><sub>fl</sub>, needed when using a graphite calorimeter to derive dose to water, were determined in a clinical high-energy carbon-ion beam. Measurements were performed in a 290 MeV/n carbon-ion beam with a field size of 11 x 11 cm<sup>2</sup>, without modulation. In order to sample the beam, a plane-parallel Roos ionization chamber was chosen for its small collecting volume in comparison with the field size...
February 17, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28202324/polarity-and-ion-recombination-corrections-in-continuous-and-pulsed-beams-for-ionization-chambers-with-high-z-chamber-walls
#5
Ghada Aldosary, Habib Safigholi, William Song, Jan Seuntjens, Arman Sarfehnia
In this work, the response of Farmer-type ionization chambers fitted with high atomic number (Z) walls is studied, and results of the effects of such walls on polarity and ion recombination correction factors in both continuous and pulsed beams are presented. Measurements were made in a continuous Co-60 beam and a pulsed 6MV linac beam using an Exradin-A12 ionization chamber fitted with the manufacturer's C-552 plastic wall, as well as geometrically identical walls made from aluminum, copper and molybdenum...
February 12, 2017: Physica Medica: PM
https://www.readbyqxmd.com/read/28199294/flow-induced-microvascular-network-formation-of-therapeutic-relevant-arteriovenous-av-loop-based-constructs-in-response-to-ionizing-radiation
#6
Volker J Schmidt, Jennifer M Covi, Christoph Koepple, Johannes G Hilgert, Elias Polykandriotis, Amir K Bigdeli, Luitpold V Distel, Raymund E Horch, Ulrich Kneser
BACKGROUND The arteriovenous (AV) loop model enables axial vascularization to gain a functional microcirculatory system in tissue engineering constructs in vivo. These constructs might replace surgical flaps for the treatment of complex wounds in the future. Today, free flaps are often exposed to high-dose radiation after defect coverage, according to guideline-oriented treatment plans. Vascular response of AV loop-based constructs has not been evaluated after radiation, although it is of particular importance...
February 15, 2017: Medical Science Monitor: International Medical Journal of Experimental and Clinical Research
https://www.readbyqxmd.com/read/28164865/the-correction-of-time-and-temperature-effects-in-mr-based-3d-fricke-xylenol-orange-dosimetry
#7
Mattea L Welch, David Jaffray
<b>Purpose:</b> MR-based three-dimensional (3D) Fricke-xylenol orange (FXG) dosimeters can provide end-to-end quality assurance and validation protocols for pre-clinical radiation platforms. FXG dosimeters quantify ionizing irradiation using pre- and post-irradiation MR imaging methods that detect changes in spin-lattice relaxation rates (R<sub>1</sub> = T<sub>1</sub><sup>-1</sup>) caused by irradiation induced oxidation of Fe<sup>2+</sup>. Chemical changes in MR-based FXG dosimeters that occur over time and with changes in temperature can decrease dosimetric accuracy if they are not properly characterized and corrected...
February 6, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28155843/analysis-of-measurement-deviations-for-the-patient-specific-quality-assurance-using-intensity-modulated-spot-scanning-particle-beams
#8
Yongqiang Li, Wen Hsi
To analyze measurement deviations of patient-specific quality assurance (QA) using intensity-modulated spot-scanning particle beams, a commercial radiation dosimeter using 24 pin-point ionization chambers was utilized. Before clinical trial, the validations of radiation dosimeter as well as treatment planning system were executed. During clinical trial 165 measurements were performed on 36 patients enrolled. Two or three fields were used for each patient. Measurements were typically performed with the dosimeter placed at special regions of dose distribution along depth and lateral profiles...
February 3, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28153673/quantitative-analysis-of-menthol-in-human-urine-using-solid-phase-microextraction-and-stable-isotope-dilution-gas-chromatography-mass-spectrometry
#9
Wenlin Huang, Benjamin C Blount, Clifford H Watson, Christina Watson, David M Chambers
To accurately measure menthol levels in human urine, we developed a method using gas chromatography/electron ionization mass spectrometry with menthol-d4 stable isotope internal standardization. We used solid phase microextraction (SPME) headspace sampling for collection, preconcentration and automation. Conjugated forms of menthol were released using β-glucuronidase/sulfatase to allow for measuring total menthol. Additionally, we processed the specimens without using β-glucuronidase/sulfatase to quantify the levels of unconjugated (free) menthol in urine...
December 13, 2016: Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences
https://www.readbyqxmd.com/read/28152195/a-2d-silicon-detector-array-for-quality-assurance-in-small-field-dosimetry-duo
#10
Khalsa Al Shukaili, Marco Petasecca, Matthew Newall, Anthony Espinoza, Vladimir L Perevertaylo, Stéphanie Corde, Michael Lerch, Anatoly B Rosenfeld
PURPOSE: Nowadays, there are many different applications that use small fields in radiotherapy treatments. The dosimetry of small radiation fields is not trivial due to the problems associated with lateral disequilibrium and source occlusion and requires reliable quality assurance (QA). Ideally such a QA tool should provide high spatial resolution, minimal beam perturbation and real time fast measurements. Many different types of silicon diode arrays are used for QA in radiotherapy; however, their application in small filed dosimetry is limited, in part, due to a lack of spatial resolution...
December 10, 2016: Medical Physics
https://www.readbyqxmd.com/read/28144120/simplified-method-for-creating-a-density-absorbed-dose-calibration-curve-for-the-low-dose-range-from-gafchromic-ebt3-film
#11
Tatsuhiro Gotanda, Toshizo Katsuda, Rumi Gotanda, Tadao Kuwano, Takuya Akagawa, Nobuyoshi Tanki, Akihiko Tabuchi, Tetsunori Shimono, Yasuyuki Kawaji
Radiochromic film dosimeters have a disadvantage in comparison with an ionization chamber in that the dosimetry process is time-consuming for creating a density-absorbed dose calibration curve. The purpose of this study was the development of a simplified method of creating a density-absorbed dose calibration curve from radiochromic film within a short time. This simplified method was performed using Gafchromic EBT3 film with a low energy dependence and step-shaped Al filter. The simplified method was compared with the standard method...
October 2016: Journal of Medical Physics
https://www.readbyqxmd.com/read/28144115/dosimetric-evaluation-of-newly-developed-well-type-ionization-chamber-for-use-in-the-calibration-of-brachytherapy-sources
#12
Sathiyan Saminathan, Henry Finlay Godson, Retna Ponmalar, Ravikumar Manickam, James Mazarello
The well-type ionization chamber has been designed for convenient use in brachytherapy source strength calibration. The chamber has a volume of 240 cm(3), weight of 2.5 kg, and is open to atmospheric conditions. The well-type ionization chamber dosimetric characteristics such as leakage current, stability, scattering effect, ion collection efficiency, and nominal response with energy were studied. The evaluated dosimetric characteristics of well-type ionization chamber were compared with two other commercially available well-type ionization chambers...
October 2016: Journal of Medical Physics
https://www.readbyqxmd.com/read/28144114/on-line-estimations-of-delivered-radiation-doses-in-three-dimensional-conformal-radiotherapy-treatments-of-carcinoma-uterine-cervix-patients-in-linear-accelerator
#13
Suman Kumar Putha, P U Saxena, S Banerjee, Challapalli Srinivas, B M Vadhiraja, Ramamoorthy Ravichandran, Mary Joan, K Dinesh Pai
Transmission of radiation fluence through patient's body has a correlation to the planned target dose. A method to estimate the delivered dose to target volumes was standardized using a beam level 0.6 cc ionization chamber (IC) positioned at electronic portal imaging device (EPID) plane from the measured transit signal (St) in patients with cancer of uterine cervix treated with three-dimensional conformal radiotherapy (3DCRT). The IC with buildup cap was mounted on linear accelerator EPID frame with fixed source to chamber distance of 146...
October 2016: Journal of Medical Physics
https://www.readbyqxmd.com/read/28134130/chemically-tuned-linear-energy-transfer-dependent-quenching-in-a-deformable-radiochromic-3d-dosimeter
#14
Ellen Marie Høye, Peter S Skyt, Peter Balling, Ludvig P Muren, Vicki T Taasti, Jan Swakoń, Gabriela Mierzwińska, Marzena Rydygier, Niels Bassler, Jørgen B B Petersen
Most solid-state detectors, including 3D dosimeters, show lower signal in the Bragg peak than expected, a process termed quenching. The purpose of this study was to investigate how variation in chemical composition of a recently developed radiochromic, silicone-based 3D dosimeter influences the observed quenching in proton beams. The dependency of dose response on linear energy transfer, as calculated through Monte Carlo simulations of the dosimeter, was investigated in 60 MeV proton beams. We found that the amount of quenching varied with the chemical composition: peak-to-plateau ratios (1 cm into the plateau) ranged from 2...
February 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28133754/examining-the-influence-of-humidity-on-reference-ionization-chamber-performance
#15
Malcolm R McEwen, Jaswinder Taank
PURPOSE: International dosimetry protocols require measurements made with a vented ionization chamber to be corrected for the influence of air density by using the standard temperature-pressure correction factor. The effect of humidity, on the other hand, is generally ignored with the provision that the relative humidity (RH) is within certain limits (typically 20% to 80%). However, there is little experimental data in the published literature as to the true effect of humidity on modern reference-class ionization chambers...
December 10, 2016: Medical Physics
https://www.readbyqxmd.com/read/28133748/commissioning-of-the-leksell-gamma-knife-%C3%A2-icon%C3%A2
#16
Michele Zeverino, Maud Jaccard, David Patin, Nick Ryckx, Maud Marguet, Constantin Tuleasca, Luis Schiappacasse, Jean Bourhis, Marc Levivier, Francois O Bochud, Raphaël Moeckli
PURPOSE: The Leksell Gamma Knife (LGK) Icon has been recently introduced to provide Gamma Knife technology with frameless stereotactic treatments which use an additional cone-beam CT (CBCT) imaging system and a motion tracking system (IFMM, Intra-Fraction Motion Management). The system was commissioned for the treatment unit itself as well as the imaging system. METHODS: The LGK Icon was calibrated using an A1SL ionization chamber. EBT3 radiochromic films were employed to independently check the machine calibration, to measure the relative output factors (ROFs) and to collect dose distributions...
December 10, 2016: Medical Physics
https://www.readbyqxmd.com/read/28111399/evaluation-of-the-positional-accuracy-and-dosimetric-properties-of-a-three-dimensional-printed-device-for-head-and-neck-immobilization
#17
Kiyokazu Sato, Ken Takeda, Suguru Dobashi, Noriyuki Kadoya, Kengo Ito, Mizuki Chiba, Kazuma Kishi, Isao Yanagawa, Keiichi Jingu
Our aim was to investigate the feasibility of a three-dimensional (3D) -printed head-and-neck (HN) immobilization device by comparing its positional accuracy and dosimetric properties with those of a conventional immobilization device (CID). We prepared a 3D-printed immobilization device (3DID) consisting of a mask and headrest with acrylonitrile-butadiene-styrene resin developed from the computed tomography data obtained by imaging a HN phantom. For comparison, a CID comprising a thermoplastic mask and headrest was prepared using the same HN phantom...
2017: Nihon Hoshasen Gijutsu Gakkai Zasshi
https://www.readbyqxmd.com/read/28108100/three-dimensional-quality-assurance-of-imrt-prostate-plans-using-gel-dosimetry
#18
M A Silveira, J F Pavoni, O Baffa
Intensity modulated radiotherapy (IMRT) is one of the most modern radiation therapy treatment techniques. Although IMRT can deliver high and complex conformational doses to the tumor volume, its implementation requires rigorous quality assurance (QA) procedures that include a dosimetric pre-treatment verification of individual patient planning. This verification usually involves measuring a small volume of absolute dose with an ionization chamber and checking bi-dimensional fluency with an array of detectors...
January 17, 2017: Physica Medica: PM
https://www.readbyqxmd.com/read/28102948/use-of-parallel-plate-ionization-chambers-in-reference-dosimetry-of-novac-and-liac-%C3%A2-mobile-electron-linear-accelerators-for-intraoperative-radiotherapy-a-multi-center-survey
#19
Paolo Scalchi, Alessia Ciccotelli, Giuseppe Felici, Assunta Petrucci, Raffaella Massafra, Valeria Piazzi, Paola D'Avenia, Francesca Cavagnetto, Federica Cattani, Raffaella Romagnoli, Antonella Soriani
PURPOSE: LIAC(®) and NOVAC are two mobile linear accelerators dedicated to intraoperative radiation therapy (IORT), generating electron beams in the energy range of 3-12 MeV. Due to high dose-per-pulse (up to 70 mGy per pulse), in 2003 the Italian National Institute of Health (ISS) stated that "for the measure of dose to water in reference conditions, ionization chambers cannot be employed and no published dosimetry protocol can be used". As a consequence, ferrous sulphate (or, alternatively alanine) dosimetry was recommended...
January 2017: Medical Physics
https://www.readbyqxmd.com/read/28102946/a-portal-dosimetry-dose-prediction-method-based-on-collapsed-cone-algorithm-using-the-clinical-beam-model
#20
J Martínez Ortega, N Gómez González, P Castro Tejero, M Pinto Monedero, N B Tolani, L Núñez Martín, R Sánchez Montero
PURPOSE: Amorphous silicon electronical portal imaging devices (EPIDs) are widely used for dosimetric measurements in Radiation Therapy. The purpose of this work was to determine if a portal dose prediction method can be utilized for dose map calculations based on the linear accelerator model within a commercial treatment planning system (Pinnacle(3) v8.0 m). METHODS: The method was developed for a 6 MV photon beam on the Varian Clinac 21-EX, at a nominal dose rate of 400 MU/min...
January 2017: Medical Physics
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