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Ion recombination corrections of ionization chambers in flattening filter‐free photon radiation

The flattening filter free (FFF) X‐rays can provide much higher dose rate at the treatment target compared to the conventional flattened X‐rays. However, the substantial increase of dose rate for FFF beams may affect the ion recombination correction factor, which is required for accurate measurement...

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Autores principales: Wang, Yuenan, Easterling, Stephen B., Ting, Joseph Y.
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/PMC5718222/
https://www.ncbi.nlm.nih.gov/pubmed/22955642
http://dx.doi.org/10.1120/jacmp.v13i5.3758
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author Wang, Yuenan
Easterling, Stephen B.
Ting, Joseph Y.
author_facet Wang, Yuenan
Easterling, Stephen B.
Ting, Joseph Y.
author_sort Wang, Yuenan
collection PubMed
description The flattening filter free (FFF) X‐rays can provide much higher dose rate at the treatment target compared to the conventional flattened X‐rays. However, the substantial increase of dose rate for FFF beams may affect the ion recombination correction factor, which is required for accurate measurements using ionization chambers in clinical dosimetry. The purpose of this work is to investigate the ion recombination of three types of commonly used ion chambers (Farmer, PinPoint and plane‐parallel) in the FFF photon radiation. Both 6 MV and 10 MV flattened and FFF beams were fully commissioned on a Varian TrueBeam linear accelerator. The ion recombination correction factor, [Formula: see text] , was determined using the two‐voltage technique for a 0.6 cc Farmer chamber, a 0.015 cc PinPoint chamber, and a 0.02 cc parallel‐plate chamber at different source‐to‐axis distances (SAD) in a solid water phantom or water tank phantom at a depth of 10 cm in a [Formula: see text] field. Good repeatability of measurements was demonstrated. Less than 1% difference in Pion between the flattened and FFF photons for all three ion chambers was observed. At a SAD of 100 cm and a depth of 10 cm for a [Formula: see text] field, [Formula: see text] for the Farmer chamber was 1.004 and 1.008 for the 6 MV flattened and FFF beams, respectively. At the same setup using the Farmer chamber, [Formula: see text] was 1.002 and 1.015 for the 10 MV flattened and FFF beams, respectively. All [Formula: see text] results for the Farmer, PinPoint, or parallel plate chamber in the 6 MV and 10 MV flattened and FFF beams were within 2% from the unity (1 ≤ [Formula: see text] < 1.02). The [Formula: see text] ratio of the FFF to flattened beams was [Formula: see text] for both 6 MV and 10 MV photons. The ion recombination effect of the Farmer, PinPoint, and plane‐parallel chamber in the FFF beams is not substantially different from that in the conventional flattened beams. PACS number: 87.56.bd
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spelling pubmed-57182222018-04-02 Ion recombination corrections of ionization chambers in flattening filter‐free photon radiation Wang, Yuenan Easterling, Stephen B. Ting, Joseph Y. J Appl Clin Med Phys Radiation Measurements The flattening filter free (FFF) X‐rays can provide much higher dose rate at the treatment target compared to the conventional flattened X‐rays. However, the substantial increase of dose rate for FFF beams may affect the ion recombination correction factor, which is required for accurate measurements using ionization chambers in clinical dosimetry. The purpose of this work is to investigate the ion recombination of three types of commonly used ion chambers (Farmer, PinPoint and plane‐parallel) in the FFF photon radiation. Both 6 MV and 10 MV flattened and FFF beams were fully commissioned on a Varian TrueBeam linear accelerator. The ion recombination correction factor, [Formula: see text] , was determined using the two‐voltage technique for a 0.6 cc Farmer chamber, a 0.015 cc PinPoint chamber, and a 0.02 cc parallel‐plate chamber at different source‐to‐axis distances (SAD) in a solid water phantom or water tank phantom at a depth of 10 cm in a [Formula: see text] field. Good repeatability of measurements was demonstrated. Less than 1% difference in Pion between the flattened and FFF photons for all three ion chambers was observed. At a SAD of 100 cm and a depth of 10 cm for a [Formula: see text] field, [Formula: see text] for the Farmer chamber was 1.004 and 1.008 for the 6 MV flattened and FFF beams, respectively. At the same setup using the Farmer chamber, [Formula: see text] was 1.002 and 1.015 for the 10 MV flattened and FFF beams, respectively. All [Formula: see text] results for the Farmer, PinPoint, or parallel plate chamber in the 6 MV and 10 MV flattened and FFF beams were within 2% from the unity (1 ≤ [Formula: see text] < 1.02). The [Formula: see text] ratio of the FFF to flattened beams was [Formula: see text] for both 6 MV and 10 MV photons. The ion recombination effect of the Farmer, PinPoint, and plane‐parallel chamber in the FFF beams is not substantially different from that in the conventional flattened beams. PACS number: 87.56.bd John Wiley and Sons Inc. 2012-09-06 /pmc/articles/PMC5718222/ /pubmed/22955642 http://dx.doi.org/10.1120/jacmp.v13i5.3758 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
Wang, Yuenan
Easterling, Stephen B.
Ting, Joseph Y.
Ion recombination corrections of ionization chambers in flattening filter‐free photon radiation
title Ion recombination corrections of ionization chambers in flattening filter‐free photon radiation
title_full Ion recombination corrections of ionization chambers in flattening filter‐free photon radiation
title_fullStr Ion recombination corrections of ionization chambers in flattening filter‐free photon radiation
title_full_unstemmed Ion recombination corrections of ionization chambers in flattening filter‐free photon radiation
title_short Ion recombination corrections of ionization chambers in flattening filter‐free photon radiation
title_sort ion recombination corrections of ionization chambers in flattening filter‐free photon radiation
topic Radiation Measurements
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5718222/
https://www.ncbi.nlm.nih.gov/pubmed/22955642
http://dx.doi.org/10.1120/jacmp.v13i5.3758
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