Experimental determination of the effective point of measurement and the displacement correction factor for cylindrical ionization chambers in a 6 MV photon beam.
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| Title: | Experimental determination of the effective point of measurement and the displacement correction factor for cylindrical ionization chambers in a 6 MV photon beam. |
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| Authors: | Legrand, C.1 c.legrand@dkfz-heidelberg.de, Hartmann, G. H.1, Karger, C. P.1 |
| Source: | Physics in Medicine & Biology. 11/7/2012, Vol. 57 Issue 21, p6869-6880. 12p. |
| Subjects: | Ionization chambers, Photon beams, Gamma rays, Correction factors, Absorption, Particle beams, Ionization (Atomic physics) |
| Abstract: | 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 theGerman 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. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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