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Experimental determination of the effective point of measurement and the displacement correction factor for cylindrical ionization chambers in a 6 MV photon beam

The displacement effect of cylindrical ionization chambers is taken into account either by an effective point of measurement (EPOM) or, alternatively, by using a displacement correction factor. The dependence of these effects on water was examined as a function of the cavity radius for 60Co gamma ra...

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Bibliographic Details
Main Authors: Legrand, Carine (Author) , Hartmann, Günther H. (Author) , Karger, Christian (Author)
Format: Article (Journal)
Language:English
Published: 5 October 2012
In: Physics in medicine and biology
Year: 2012, Volume: 57, Issue: 21, Pages: 6869-6880
ISSN:1361-6560
DOI:10.1088/0031-9155/57/21/6869
Online Access:Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1088/0031-9155/57/21/6869
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Author Notes:C Legrand, GH Hartmann and CP Karger
Description
Summary:The displacement effect of cylindrical ionization chambers is taken into account either by an effective point of measurement (EPOM) or, alternatively, by using a displacement correction factor. The dependence of these effects on water was examined as a function of the cavity radius for 60Co gamma radiation in a previous paper. This paper describes results for high-energy photon beams using the same measurement technique. Additionally, the displacement correction factor was directly measured. Absorbed doses measured under reference conditions following the international protocol IAEA TRS-398 and the German protocol DIN 6800-2 agreed well between the chambers with different cavity radii within a standard uncertainty of 0.2%. However, there was a constant difference of 0.2% between both protocols. Similar to our observations made in 60Co, absorbed doses measured with the different chambers at depths beyond the maximum showed deviations of up to 0.6% and 0.5% for IAEA TRS-398 and DIN 6800-2, respectively, and deviations of more than 1% were found for both protocols in the build-up and maximum region. We therefore propose modified formulas for the determination of the EPOM and the displacement correction factor.
Item Description:Gesehen am 17.01.2022
Physical Description:Online Resource
ISSN:1361-6560
DOI:10.1088/0031-9155/57/21/6869

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