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Dose calibration of EPIDs for segmented IMRT dosimetry

The purpose of this study was to investigate the dose response of amorphous silicon (a‐Si) electronic portal imaging devices (EPIDs) under different acquisition settings for both open jaw defined fields and segmented intensity‐modulated radiation therapy (IMRT) fields. Four different EPIDs were used...

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Autores principales: Deshpande, Shrikant, Xing, Aitang, Holloway, Lois, Metcalfe, Peter, Vial, Philip
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2014
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5711103/
https://www.ncbi.nlm.nih.gov/pubmed/25493513
http://dx.doi.org/10.1120/jacmp.v15i6.4895
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author Deshpande, Shrikant
Xing, Aitang
Holloway, Lois
Metcalfe, Peter
Vial, Philip
author_facet Deshpande, Shrikant
Xing, Aitang
Holloway, Lois
Metcalfe, Peter
Vial, Philip
author_sort Deshpande, Shrikant
collection PubMed
description The purpose of this study was to investigate the dose response of amorphous silicon (a‐Si) electronic portal imaging devices (EPIDs) under different acquisition settings for both open jaw defined fields and segmented intensity‐modulated radiation therapy (IMRT) fields. Four different EPIDs were used. Two Siemens and one Elekta plus a standalone Perkin Elmer research EPID. Each was operated with different acquisition systems and settings. Dose response linearity was measured for open static jaw defined fields and ‘simple’ segmented IMRT fields for a range of equipment and system settings. Six ‘simple’ segmented IMRT fields were used. The segments of each IMRT field were fixed at [Formula: see text] field size with equal MU per segment, each field having a total of 20 MU. Simultaneous measurements with an ionization chamber array (ICA) and EPID were performed to separate beam and detector response characteristics. Three different pixel calibration methods were demonstrated and compared for an example ‘clinical IMRT field’. The dose response with the Elekta EPID for ‘simple’ segmented IMRT fields versus static fields agreed to within 2.5% for monitor unit [Formula: see text]. The dose response for the Siemens systems was difficult to interpret due to the poor reproducibility for segmented delivery, at [Formula: see text] , which was not observed with the standalone research EPID nor ICA on the same machine. The dose response measured under different acquisition settings and different linac/EPID combinations matched closely ([Formula: see text]), except for the Siemens EPID. Clinical IMRT EPID dosimetry implemented with the different pixel‐to‐dose calibration methods indicated that calibration at 20 MU provides equivalent results to implementing a ghosting correction model. The nonlinear dose response was consistent across both clinical EPIDs and the standalone research EPID, with the exception of the poor reproducibility seen with Siemens EPID images of IMRT fields. The nonlinear dose response was relatively insensitive to acquisition settings and appears to be primarily due to gain ghosting effects. No additional ghosting correction factor is necessary when the pixel‐to‐dose calibration factor at small MU calibration method is used. PACS numbers: 87.53.Bn, 87.55.Qr, 87.56.Fc, 87.57.uq
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spelling pubmed-57111032018-04-02 Dose calibration of EPIDs for segmented IMRT dosimetry Deshpande, Shrikant Xing, Aitang Holloway, Lois Metcalfe, Peter Vial, Philip J Appl Clin Med Phys Radiation Oncology Physics The purpose of this study was to investigate the dose response of amorphous silicon (a‐Si) electronic portal imaging devices (EPIDs) under different acquisition settings for both open jaw defined fields and segmented intensity‐modulated radiation therapy (IMRT) fields. Four different EPIDs were used. Two Siemens and one Elekta plus a standalone Perkin Elmer research EPID. Each was operated with different acquisition systems and settings. Dose response linearity was measured for open static jaw defined fields and ‘simple’ segmented IMRT fields for a range of equipment and system settings. Six ‘simple’ segmented IMRT fields were used. The segments of each IMRT field were fixed at [Formula: see text] field size with equal MU per segment, each field having a total of 20 MU. Simultaneous measurements with an ionization chamber array (ICA) and EPID were performed to separate beam and detector response characteristics. Three different pixel calibration methods were demonstrated and compared for an example ‘clinical IMRT field’. The dose response with the Elekta EPID for ‘simple’ segmented IMRT fields versus static fields agreed to within 2.5% for monitor unit [Formula: see text]. The dose response for the Siemens systems was difficult to interpret due to the poor reproducibility for segmented delivery, at [Formula: see text] , which was not observed with the standalone research EPID nor ICA on the same machine. The dose response measured under different acquisition settings and different linac/EPID combinations matched closely ([Formula: see text]), except for the Siemens EPID. Clinical IMRT EPID dosimetry implemented with the different pixel‐to‐dose calibration methods indicated that calibration at 20 MU provides equivalent results to implementing a ghosting correction model. The nonlinear dose response was consistent across both clinical EPIDs and the standalone research EPID, with the exception of the poor reproducibility seen with Siemens EPID images of IMRT fields. The nonlinear dose response was relatively insensitive to acquisition settings and appears to be primarily due to gain ghosting effects. No additional ghosting correction factor is necessary when the pixel‐to‐dose calibration factor at small MU calibration method is used. PACS numbers: 87.53.Bn, 87.55.Qr, 87.56.Fc, 87.57.uq John Wiley and Sons Inc. 2014-11-08 /pmc/articles/PMC5711103/ /pubmed/25493513 http://dx.doi.org/10.1120/jacmp.v15i6.4895 Text en © 2014 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 Oncology Physics
Deshpande, Shrikant
Xing, Aitang
Holloway, Lois
Metcalfe, Peter
Vial, Philip
Dose calibration of EPIDs for segmented IMRT dosimetry
title Dose calibration of EPIDs for segmented IMRT dosimetry
title_full Dose calibration of EPIDs for segmented IMRT dosimetry
title_fullStr Dose calibration of EPIDs for segmented IMRT dosimetry
title_full_unstemmed Dose calibration of EPIDs for segmented IMRT dosimetry
title_short Dose calibration of EPIDs for segmented IMRT dosimetry
title_sort dose calibration of epids for segmented imrt dosimetry
topic Radiation Oncology Physics
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5711103/
https://www.ncbi.nlm.nih.gov/pubmed/25493513
http://dx.doi.org/10.1120/jacmp.v15i6.4895
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