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Errors introduced by dose scaling for relative dosimetry

Some dosimeters require a relationship between detector signal and delivered dose. The relationship (characteristic curve or calibration equation) usually depends on the environment under which the dosimeters are manufactured or stored. To compensate for the difference in radiation response among di...

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Detalles Bibliográficos
Autores principales: Watanabe, Yoichi, Hayashi, Naoki
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2012
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5718219/
https://www.ncbi.nlm.nih.gov/pubmed/22955658
http://dx.doi.org/10.1120/jacmp.v13i5.3930
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author Watanabe, Yoichi
Hayashi, Naoki
author_facet Watanabe, Yoichi
Hayashi, Naoki
author_sort Watanabe, Yoichi
collection PubMed
description Some dosimeters require a relationship between detector signal and delivered dose. The relationship (characteristic curve or calibration equation) usually depends on the environment under which the dosimeters are manufactured or stored. To compensate for the difference in radiation response among different batches of dosimeters, the measured dose can be scaled by normalizing the measured dose to a specific dose. Such a procedure, often called “relative dosimetry”, allows us to skip the time‐consuming production of a calibration curve for each irradiation. In this study, the magnitudes of errors due to the dose scaling procedure were evaluated by using the characteristic curves of BANG3 polymer gel dosimeter, radiographic EDR2 films, and GAFCHROMIC EBT2 films. Several sets of calibration data were obtained for each type of dosimeters, and a calibration equation of one set of data was used to estimate doses of the other dosimeters from different batches. The scaled doses were then compared with expected doses, which were obtained by using the true calibration equation specific to each batch. In general, the magnitude of errors increased with increasing deviation of the dose scaling factor from unity. Also, the errors strongly depended on the difference in the shape of the true and reference calibration curves. For example, for the BANG3 polymer gel, of which the characteristic curve can be approximated with a linear equation, the error for a batch requiring a dose scaling factor of 0.87 was larger than the errors for other batches requiring smaller magnitudes of dose scaling, or scaling factors of 0.93 or 1.02. The characteristic curves of EDR2 and EBT2 films required nonlinear equations. With those dosimeters, errors larger than 5% were commonly observed in the dose ranges of below 50% and above 150% of the normalization dose. In conclusion, the dose scaling for relative dosimetry introduces large errors in the measured doses when a large dose scaling is applied, and this procedure should be applied with special care. PACS numbers: 87.56.Da, 06.20.Dk, 06.20.fb
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spelling pubmed-57182192018-04-02 Errors introduced by dose scaling for relative dosimetry Watanabe, Yoichi Hayashi, Naoki J Appl Clin Med Phys Radiation Measurements Some dosimeters require a relationship between detector signal and delivered dose. The relationship (characteristic curve or calibration equation) usually depends on the environment under which the dosimeters are manufactured or stored. To compensate for the difference in radiation response among different batches of dosimeters, the measured dose can be scaled by normalizing the measured dose to a specific dose. Such a procedure, often called “relative dosimetry”, allows us to skip the time‐consuming production of a calibration curve for each irradiation. In this study, the magnitudes of errors due to the dose scaling procedure were evaluated by using the characteristic curves of BANG3 polymer gel dosimeter, radiographic EDR2 films, and GAFCHROMIC EBT2 films. Several sets of calibration data were obtained for each type of dosimeters, and a calibration equation of one set of data was used to estimate doses of the other dosimeters from different batches. The scaled doses were then compared with expected doses, which were obtained by using the true calibration equation specific to each batch. In general, the magnitude of errors increased with increasing deviation of the dose scaling factor from unity. Also, the errors strongly depended on the difference in the shape of the true and reference calibration curves. For example, for the BANG3 polymer gel, of which the characteristic curve can be approximated with a linear equation, the error for a batch requiring a dose scaling factor of 0.87 was larger than the errors for other batches requiring smaller magnitudes of dose scaling, or scaling factors of 0.93 or 1.02. The characteristic curves of EDR2 and EBT2 films required nonlinear equations. With those dosimeters, errors larger than 5% were commonly observed in the dose ranges of below 50% and above 150% of the normalization dose. In conclusion, the dose scaling for relative dosimetry introduces large errors in the measured doses when a large dose scaling is applied, and this procedure should be applied with special care. PACS numbers: 87.56.Da, 06.20.Dk, 06.20.fb John Wiley and Sons Inc. 2012-09-06 /pmc/articles/PMC5718219/ /pubmed/22955658 http://dx.doi.org/10.1120/jacmp.v13i5.3930 Text en © 2012 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 Radiation Measurements
Watanabe, Yoichi
Hayashi, Naoki
Errors introduced by dose scaling for relative dosimetry
title Errors introduced by dose scaling for relative dosimetry
title_full Errors introduced by dose scaling for relative dosimetry
title_fullStr Errors introduced by dose scaling for relative dosimetry
title_full_unstemmed Errors introduced by dose scaling for relative dosimetry
title_short Errors introduced by dose scaling for relative dosimetry
title_sort errors introduced by dose scaling for relative dosimetry
topic Radiation Measurements
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5718219/
https://www.ncbi.nlm.nih.gov/pubmed/22955658
http://dx.doi.org/10.1120/jacmp.v13i5.3930
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