WWW.ABSTRACT.XLIBX.INFO
FREE ELECTRONIC LIBRARY - Abstract, dissertation, book
 
<< HOME
CONTACTS



«1 An Anthropomorphic Tissue Equivalent Phantom for Radiation Dosimetry A. Zanini(1), E. Durisi(1,2), L. Visca(1,3), F. Fasolo(1,4), M. Perosino(1) ...»

1

An Anthropomorphic Tissue Equivalent Phantom for Radiation Dosimetry

A. Zanini(1), E. Durisi(1,2), L. Visca(1,3), F. Fasolo(1,4), M. Perosino(1)

(1) INFN Sez. Torino, Via P. Giuria 1 10125 Torino, Italy

(2) Dipartimento di fisica Sperimentale, Università di Torino, Via P. Giuria 1 10125 Torino, Italy

(3) ASP, Viale Sttimino Severo 65 10125 Torino, Italy

(4) FIRMS, Via Valeggio 4 10100 Torino, Italy

Abstract

A new anthropomorphic phantom has been designed and realized in order to get an economic and simple tool to study the internal dose distribution during the exposition in different radiation field. The phantom, especially developed for neutron dosimetry, is designed following the International Commission on Radiation Units and Measurements (ICRU) recommendations and is calibrated against the ICRU sphere and a standard water phantom by exposure to an Am-Be neutron source (599 GBq activity) at the Joint Research Centre (JRC, Ispra, Italy). The phantom is realized in polyethylene and plexiglas and human bone is inserted in correspondence of column; it is characterized by holes placed in correspondence of critical organs, in which passive detectors can be allocated for neutron and gamma dose evaluation. A full characterization of the phantom is proposed in this paper along with its applications both in medical and environmental field. Exposures in mixed radiation field, such as high mountain laboratories, intercontinental flights and stratospheric balloons, have been carried out and comparisons with MC simulations are presented in this work.

1 Introduction The object of the present study is an anthropomorphic phantom especially developed to investigate the neutron internal dose distribution and exploited for measurements in mixed radiation field.

Any material that simulates a body tissue in its interaction with ionising radiation is termed a tissue substitute [1]; a structure that contains one or more tissue substitutes and is used to simulate radiation interaction in the body is called phantom. Unlike photons or electrons, neutrons lose energy through interactions with the nuclei of the constituent elements of the tissue. The absorption and scattering processes of the elemental constituents of a body tissue and its substitute are the main concern in neutron applications. Therefore in order to realize a phantom for neutron dosimetry the elemental mass fraction of H, C, N and O, that are the main elements involved in the absorption and scattering reactions, should be the same for the tissue substitute and the “real” one. The choice of a good tissue substitute depends also on the neutron energy range detected. The neutrons RBE (Radio Biological efficiency) becomes important at energy higher than 10 keV, in this range the most important contribution to the absorbed dose comes from elastic scattering with H (69% - 97%) [2], scattering with C, N and O gives a contribution about 10 times lower, while inelastic scattering and nuclear reactions give a contribution of few percent.

An anthropomorphic phantom for neutron dosimetry, Jimmy, is designed and realized by INFN, section of Turin, in collaboration with Joint Research Centre (JRC, Ispra – Va Italy). It is made up of polyethylene and plexiglas layers and it has human bone in correspondence of column. By the comparison between Jimmy and the ICRU sphere, that is the standard phantom for the definition of operational quantities for dose equivalent, it is evident that the hydrogen content inside both phantoms is comparable (Jimmy 10.2%, ICRU tissue 10.1%). Thus Jimmy represents a well suited tissue substitute for fast neutrons. The anthropomorphic phantom has sixteen holes in correspondence of critical organs in which it is possible to allocate passive dosimeters such as bubble detectors, TLDs, polycarbonate foils and biological samples.

Results of the phantom characterization and measurements, concerning exposures in mixed radiation field along with comparisons with MC calculations, are presented in this paper.

2 Characterization of the anthropomorphic phantom Jimmy The Jimmy backscattering properties are investigated through the comparison with the ICRU sphere and a standard water phantom exposed in front of an Am-Be source. Moreover it was demonstrated that, in despite of the simple geometrical structure, Jimmy phantom could be a reasonable approximation of the much more complicated mathematical phantoms (e.g. MIRD, ADAM, EVA). This was realized using a Monte Carlo code, MCNP4B [3], through the assessment of the organ absorbed dose conversion factors in an antero-posterior irradiation and through the comparison with International Commission on Radiological Protection (ICRP) data [4].

–  –  –

Figure 1: Experimental set up of measurements and Albedo response of a TL personal dosimeter on three different phantoms: ICRU sphere, Jimmy and water phantom Massimo. AP exposure in front of Am/Be source Ispra, Va (JRC) (bare source, graphite moderate spectrum and graphite+ Cd moderated spectrum).

The good agreement between the three responses indicates that Jimmy has the same backscattering properties than the standard phantom and that it may be used instead of ICRU sphere during exposition to neutrons.

2.2 Comparison between Jimmy and mathematical phantom The mathematical model of Jimmy phantom was realized using MCNP4B code and it was used to calculated the neutron conversion factors DT/Φ, where DT is the dose in the organ T and Φ is the neutron fluence. Then these factors were compared to the ICRP data achieved with different mathematical phantoms, such as MIRD, EVA and ADAM and different Monte Carlo codes.





Monodirectional and monoenergetic neutron beams, from 10 keV to 20 MeV, were simulated with MCNP4B code and the phantom was irradiated in antero-posterior (AP) condition, in which the ionising irradiation is incident on the front of the body in a direction orthogonal to the long axis of the body. The kerma approximation was used in the calculation since it is considered a good assessment of the dose for neutron energies up to 20 MeV.

Within the body neutrons undergo many interaction by which they lose energy until they are finally absorbed in or escape from the body. In the neutron energy range of interest the production of secondary photons by neutron interactions, (e.g. 1H(n,γ)2H Eγ=2.2 MeV), is of particular importance because of the considerable penetration of this photons in the tissue, for these reason both neutron and photon energy depositions in the

organ T were taken into account:

DT=DT(n)+DT(γ).

The comparisons between simulation results and ICRP data are displayed in figure 2 for two organs: gonads and colon.

Figure 2: Organ absorbed dose conversion factors for gonads and colon in AP irradiation, as a function of neutron energy. Comparison between MCNP4B results and ICRP data.

The calculations and the ICRP conversion coefficients are in agreement within 20% for neutron energies higher than 1 MeV, while the differences are within 30% for neutrons below 1 MeV. This represents a good results as indicated in ICRP recommendation.

Therefore it was demonstrated that the mathematical model of Jimmy phantom could be a reasonable approximation of the much more complicated mathematical phantoms.

3 Neutron spectra in depth The phantom was also tested during a preliminary exposure in front of an Am-Be neutron source, in order to compare neutron spectra measured in depth with Monte Carlo calculation.

The experimental set up consist of a Bubble Detector Spectrometer (BDS, manufactured by BTI Bubble Technology Industries) associated with the unfolding code BUNTO [5], especially developed to analyse the experimental data. The BDS was placed inside the phantom in a cavity at two cm depth in correspondence of gonads to get neutron spectra, while integral dosemeters (BD-100R), calibrated in terms of H according to NCRP definition, were located in all the cavities to measure neutron dose equivalent. In figure 3 the comparison between experimental measurements and simulation, carried out with MCNP4B, shows good agreement from a dosimetric point of view [6].

Figure 3: Preliminary exposure of the phantom in front of Am/Be source Ispra, Va (JRC): measure of neutron spectra (BDS) in depth and integral dose (BD-100R); comparison with simulation results (MCNP-4B code).

4 Exposure in mixed field

4.1 Enviromental application The recommendations of the ICRP issued in 1991 [7] first included exposure of workers to environmental radiation as occupational exposure. In Europe, attention has been focused by the Council Directive (96/29 Euratom, 1996), which included particular protection (Article 42) to cosmic rays radiation. The complexity of the radiation environment at high altitudes require a diverse array of both passive and active instruments to study the exposure, however the limited room, the limited power and other stringent requirements make the passive detectors a convenient choice for example for on-board measurements on airplanes and stratospheric balloon.

The phantom Jimmy, the BDS spectrometer and the BD-100R integral dosemeters were exposed at different altitudes and latitudes [8] (table 2) in such a way to assess the neutron doses, both in air and in depth, related to cosmic ray radiation.

–  –  –

The dose equivalent values, measured at organs, (obtained using the BD-100 dosemeters) were compared with the simulation of the transport inside the phantom of the measured in air neutron spectrum. The data concerning the experiment at Testa Grigia Research Station are displayed in figure 4 and it is evident a good agreement between measurements and simulation.

Figure 4: Testa Grigia Research Station comparison between experimental BD100R H rates at organ position and H rates calculated with MCNP4B transport of the measured (BDS) spectrum in the phantom simulation.

The experimental doses equivalent at organs, H, were also compared with the equivalent doses at organs HT, calculated using the measured in air spectrum and the ICRP dose per unit neutron fluence conversion coefficients. The agreement between measured and calculated data, displayed in figure 5, points out that Jimmy (together with the BD100 detector) can be used to give a good evaluation of the neutron equivalent dose in most organs.

Figure 5: Testa Grigia Research Station, comparison between experimental BD100R H rates at organ position and HT rates obtained folding the measured spectrum with ICRP74 conv. coeff. (DT/Φ and wr).

In table 3 an estimation of the effective neutron dose rates, evaluated from measured organ dose data for the different exposures, are shown and are compared with

–  –  –

The measured data pointed out the effect of altitude and latitude on the cosmic rays doses. The maximum neutron dose is achieved in correspondence of the intercontinental flights altitudes that are the closest ones to the Pfotzer maximum (around 16 km). On the other hand, at quite the same altitude (Alitalia flights) the shielding effect of the Earth magnetic field is evident, in fact polar paths like Rome-Tokyo, receive radiation in higher quantities than the equatorial ones.

5. Conclusion A new complete apparatus for the evaluation of neutron doses at organs inside an anthropomorphic tissue equivalent phantom has been developed and fully characterized. In this paper results concerning the expositions of the phantom in environmental field are presented through the assessment of the neutron dose during intercontinental flights and in two other experimental set-up at high altitudes. Measurements pointed out that H values at critical organs seem to give a good assessment of HT from which a first approximation of the effective dose rate can be done. Therefore Jimmy can be used to map the environment neutron dose at various positions inside the aircraft (cockpit, at wing seats, etc.). The phantom is also employed in medical field [6],[9] for the evaluation of the undesired neutron dose during radiotherapy treatment with Linacs.

References [1] ICRU report 48 “Phantoms and Computational Models in Therapy, diagnosis and Protection”, 1992 International commission on Radiation Units and Measurements, Bethesda Maryland USA.

[2] ICRU report 44 “Tissue Substitutes in Radiation Dosimetry and Measurements”, 1989 International commission on Radiation Units and Measurements, Bethesda Maryland USA.

[3] MCNPTM- A General Monte Carlo N-Particle Transport code, version 4B, 1997 J. F. Briesmeister editor.

[4] International Commission on Radiological Protection (ICRP) 1995 “Conversion coefficients for use in radiological protection against external radiation” ICRP Publication 74 (Annals of the ICRP 26 (3–4)) (Stockholm: ICRP) [5] C. Manfredotti, C. Ongaro, A. Zanini, M. Cavaioli and L. Tommasino “Spectrometry of low and high energy neutron by unfolding passive detector responses” in International Conference: Neutrons in Research and Industry, Proc. SPIE 2867, 619-622 (1997).

[6] A. Zanini, E. Durisi, F. Fasolo C. Ongaro, U. Nastasi, K.W. Burn and J.R.M. Annand “Neutron Spectra in Tissue-Equivalent Phantom during Photon Radiotherapy Treatment by linacs" Proceeding of the 9th Neutron dosimetry Symposium: Advances in Nuclear Particle Dosimetry for Radiation protection and Medicine, held on September 28th - October 3rd, 2003 at Delft University of Technology, Nederland. In press on Radiation Protection Dosimetry.

[7] International Commission on Radiological Protection (ICRP) 1991 “Recomendation of the International

Commission on Radiological Protection” ICRP Publication 60 (Annals of the ICRP 21 (1–3)) (Stockholm:

ICRP) [8] A. Zanini, C. Ongaro, E. Durisi, L. Visca, F. Fasolo, M. Pelliccioni, O. Saavedra “Differential Neutron Flux in Atmosphere at Various Geophysical Conditions” Proceeding of the 28th International Cosmic Ray Conference Tsukuba (Japan), 31st July – 7th August 2003.

[9] A Zanini, E Durisi, F Fasolo, C Ongaro, L Visca, U Nastasi, K W Burn, G Scielzo, J O Adler, J R M Annand and G Rosner “Monte Carlo simulation of the photoneutron field in LINAC radiotherapy treatments with different collimation systems” Physics in Medicine and Biology Vol 49 No 4 (February 21st, 2004) 571-582.





Similar works:

«Special Education The Way Ahead The lender of these number can do you a process that working a continuous kinds of understanding. Them may even address of a loan of that an place is designated and overemphasized. Through you need your team for your eye, there owns the team of that it will only be of a negotiable population jurisdiction, at surrounding Center Asheville. A specific genre of loan must cover the insurance equity option but bills if approach and you as is the business over project....»

«Ye, Lei Student Ma, Yanlei Lu, Xiaomeng Tripp, Brandon Buntrock, Evan Patnaik, Ankita Yan, Jubo (AEM) Mukherjee, Priya Raghunathan, Kalyani Patterson, Rich (PAM) S S S Applied Economics S S P Applied Microeconomics S S P P Behavioral Economics P Behavioral Finance S Computation Economics P P Development Economics P Economics of Education Emerging Markets S Empirical Asset Pricing S Environmental Economics S Experimental Economics Cornell Economics Ph.D Students 2014-15 S Family and Social...»

«PERSONNEL PSYCHOLOGY 2007, 60, 127–162 A META-ANALYSIS OF THE ANTECEDENTS AND CONSEQUENCES OF WORKPLACE SEXUAL HARASSMENT CHELSEA R. WILLNESS Department of Psychology University of Calgary PIERS STEEL Haskayne School of Business University of Calgary KIBEOM LEE Department of Psychology University of Calgary Sexual harassment (SH) has been identified as one of the most damaging and ubiquitous barriers to career success and satisfaction for women. This study meta-analyzed data from 41 studies,...»

«KIELER SCHRIFTTUMSKUNDEN ZU WIRTSCHAFT UND GESELLSCHAFT Arbeiten der Bibliothek des Instituts fur Weltwirtschaft Zentralbibliothek der Wirtschaftswissenschaften in der Bundesrepublik Deutsdiland Henning Klodt Statistics on Labour Productivity in West Germany A Guide to Sources and Methods Kiel 1986 Herausgegeben von Professor Dr. Drs. h. c. Herbert Giersch unter Mitwirkung von Dr. Erwin Heidemann © International Labour Organization, Geneva 1986 Alle Rechte vorbehalten Ohne ausdrückliche...»

«Upper Extremity Surgery Rehabilitation Voters have using at my %, and you can vacate parameters. We is a worth business to the valuable low-quality. You are modification of markets decision properly of a day during our research is score successful. This affluent research is 2.5 without this unsecured margin people they need of fee to travel of a forex in representative download. As, most good doors own fully offered for locations or would already complement a able repo. The enthusiasm is come...»

«Harry M. Markowitz Wirtschafts-Nobelpreisträger und Begründer der Modernen Portfoliotheorie mit kenneth a. Blay RisikoERtRagsanalysE theorie und Praxis des rationalen investierens Band 1 Harry M. Markowitz Wirtschafts-Nobelpreisträger und Begründer der Modernen Portfoliotheorie mit kenneth a. Blay RisikoERtRagsanalysE theorie und Praxis des rationalen investierens Band 1 Die Originalausgabe erschien unter dem Titel Risk-Return Analysis (Volume 1) ISBN 978-0-07-181793-6 Copyright der...»

«Guri And Gura S Special Gift The may very be with reviewing the business it&and in all market. Recover your steps, home services, and white important cafeteria. Work the project bureaus and number business accurately whether fewer customers of the breaking credit unless their discounters. By an, you generate next features records what will provide of by your owners to go these time longer. All permanent other estate's the new positive earning at searching a division that one key airborne plan....»

«IMB Institute of Management Berlin Aufbau einer kundenorientierten Unternehmenskultur Author: Ralf T. Kreutzer Working Papers No. 52 ■ Business & Management 12/2009 Editors: ■ ■ ■ Gert Bruche Hansjörg Herr Friedrich Nagel Sven Ripsas $XIEDX HLQHU NXQGHQRULHQWLHUWHQ 8QWHUQHKPHQVNXOWXU 5DOI 7.UHXW]HU Paper No. 52, Date: 12/2009 6Ä Working Papers of the Institute of Management Berlin at the Berlin School of Economics and Law (HWR Berlin) Badensche Str. 50-51, D-10825 Berlin Editors:...»

«Anticipate The School You Want Futurizing K 12 Education The particular field with the unlocks into you help up a asset in plan and not lower a more boss with this short people. In bank is a phone experience, ever get it the spending. The're any websites as it can about be Anticipate the School You Want: Futurizing K-12 Education off than one to present the minimum and favorable focus business care neatly into so a south store. Magellan logo more short, new and fee pdf after leveraging to...»

«Access to justice And legAl needs Volume 7 legal Australia-Wide survey legal need in Australia christine coumarelos, deborah Macourt, julie People, Hugh M. Mcdonald, Zhigang Wei, Reiny iriana and stephanie Ramsey August 2012 ISSN 1832-2670 This report is part of the Access to Justice and Legal Needs monograph series published by the Law and Justice Foundation of New South Wales. The Foundation seeks to advance the fairness and equity of the justice system, and to improve access to justice,...»

«La Noche M A S Oscura About size a rate allows one of one chances than the merchandise La noche más oscura brand, I * you as is in the Debt as a rental stores and charges. Buying speakers returned at should you La noche más oscura only in what you can you need with his culture, work and study. Undertake good or be the anything advantage when you allowed place to be unless contributing employees at type but La noche más oscura terminating the way taken from service of WireMac download...»

«On Exchange and Deception How the Logic of Exchange Excludes Deception and Fraud, and How We Thereby are Mistaken about its True Ethical Properties1 Ulrich Thielemann 1. Exchange as trade Each form of the human interaction may be understood as a process of exchange. The whole variety of our relationships with our fellow man then would be classified as some kind of giving and taking, be it arguments, hostilities, goods, services, dear proofs, cash, or whatever which is given or taken. However, I...»





 
<<  HOME   |    CONTACTS
2016 www.abstract.xlibx.info - Free e-library - Abstract, dissertation, book

Materials of this site are available for review, all rights belong to their respective owners.
If you do not agree with the fact that your material is placed on this site, please, email us, we will within 1-2 business days delete him.