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Constancy checks of well‐type ionization chambers with external‐beam radiation units

Constancy checks of a well‐type ionization chamber should be performed regularly as part of a quality assurance regime. The goal of this work was to test the feasibility of using a linear accelerator and an orthovoltage unit to check the constancy of a well‐type chamber's response to an externa...

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Autores principales: Hackett, Sara L., Davis, Benjamin, Nixon, Andrew, Wyatt, Ruth
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2015
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5691027/
https://www.ncbi.nlm.nih.gov/pubmed/26699571
http://dx.doi.org/10.1120/jacmp.v16i6.5608
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author Hackett, Sara L.
Davis, Benjamin
Nixon, Andrew
Wyatt, Ruth
author_facet Hackett, Sara L.
Davis, Benjamin
Nixon, Andrew
Wyatt, Ruth
author_sort Hackett, Sara L.
collection PubMed
description Constancy checks of a well‐type ionization chamber should be performed regularly as part of a quality assurance regime. The goal of this work was to test the feasibility of using a linear accelerator and an orthovoltage unit to check the constancy of a well‐type chamber's response to an external radiation source. The reproducibility, linearity with dose, variation with dose‐rate, and variation between energy‐matched units of the well‐type chamber response when exposed to 6 MV beams was examined. The robustness to errors in establishing the measurement conditions, including setting the source‐to‐surface distance and gantry angle, rotation of the chamber around the central axis of the beam, and the effect of changing the length of the chamber cable exposed to the field, were tested. The reproducibility and linearity with dose of the chamber response, and robustness to errors in establishing the measurement conditions for 100 kVp and 250 kVp beams from an orthovoltage unit, were also examined. The combined uncertainty, including contributions from errors in establishing the reference conditions, for well‐type chamber measurements using a 6 MV beam from a linear accelerator is 1.0%. The combined uncertainties for measurements using 100 and 250 kVp beams were 1.8% and 1.5%, respectively. When focus‐source distance errors were reduced to [Formula: see text] , the combined uncertainties for the 100 and 250 kVp beams were 1.2% and 1.1%, respectively, when the dose to the chamber was confined to the linear region of the dose‐response curve. The response of a well‐type chamber should remain constant to within 1.2% when exposed to a constant dose from an external beam unit, if reference conditions can be reproducibly established. However, the uncertainty for establishing reference conditions for output measurements for an orthovoltage unit can be reduced, which would justify a reduction of the tolerance for constancy measurements. PACS numbers: 87.55.Qr, 87.56.Fc
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spelling pubmed-56910272018-04-02 Constancy checks of well‐type ionization chambers with external‐beam radiation units Hackett, Sara L. Davis, Benjamin Nixon, Andrew Wyatt, Ruth J Appl Clin Med Phys Technical Notes Constancy checks of a well‐type ionization chamber should be performed regularly as part of a quality assurance regime. The goal of this work was to test the feasibility of using a linear accelerator and an orthovoltage unit to check the constancy of a well‐type chamber's response to an external radiation source. The reproducibility, linearity with dose, variation with dose‐rate, and variation between energy‐matched units of the well‐type chamber response when exposed to 6 MV beams was examined. The robustness to errors in establishing the measurement conditions, including setting the source‐to‐surface distance and gantry angle, rotation of the chamber around the central axis of the beam, and the effect of changing the length of the chamber cable exposed to the field, were tested. The reproducibility and linearity with dose of the chamber response, and robustness to errors in establishing the measurement conditions for 100 kVp and 250 kVp beams from an orthovoltage unit, were also examined. The combined uncertainty, including contributions from errors in establishing the reference conditions, for well‐type chamber measurements using a 6 MV beam from a linear accelerator is 1.0%. The combined uncertainties for measurements using 100 and 250 kVp beams were 1.8% and 1.5%, respectively. When focus‐source distance errors were reduced to [Formula: see text] , the combined uncertainties for the 100 and 250 kVp beams were 1.2% and 1.1%, respectively, when the dose to the chamber was confined to the linear region of the dose‐response curve. The response of a well‐type chamber should remain constant to within 1.2% when exposed to a constant dose from an external beam unit, if reference conditions can be reproducibly established. However, the uncertainty for establishing reference conditions for output measurements for an orthovoltage unit can be reduced, which would justify a reduction of the tolerance for constancy measurements. PACS numbers: 87.55.Qr, 87.56.Fc John Wiley and Sons Inc. 2015-11-08 /pmc/articles/PMC5691027/ /pubmed/26699571 http://dx.doi.org/10.1120/jacmp.v16i6.5608 Text en © 2015 The Authors. This is an open access article under the terms of the Creative Commons Attribution (http://creativecommons.org/licenses/by/3.0/) License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Technical Notes
Hackett, Sara L.
Davis, Benjamin
Nixon, Andrew
Wyatt, Ruth
Constancy checks of well‐type ionization chambers with external‐beam radiation units
title Constancy checks of well‐type ionization chambers with external‐beam radiation units
title_full Constancy checks of well‐type ionization chambers with external‐beam radiation units
title_fullStr Constancy checks of well‐type ionization chambers with external‐beam radiation units
title_full_unstemmed Constancy checks of well‐type ionization chambers with external‐beam radiation units
title_short Constancy checks of well‐type ionization chambers with external‐beam radiation units
title_sort constancy checks of well‐type ionization chambers with external‐beam radiation units
topic Technical Notes
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5691027/
https://www.ncbi.nlm.nih.gov/pubmed/26699571
http://dx.doi.org/10.1120/jacmp.v16i6.5608
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