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Influence of ion chamber response on in‐air profile measurements in megavoltage photon beams
Author(s) -
Tonkopi E.,
McEwen M. R.,
Walters B. R. B.,
Kawrakow I.
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2011090
Subject(s) - ionization chamber , photon , dosimetry , optics , ion , physics , medical physics , nuclear physics , atomic physics , materials science , nuclear medicine , ionization , medicine , quantum mechanics
This article presents an investigation of the influence of the ion chamber response, including buildup caps, on the measurement of in‐air off‐axis ratio (OAR) profiles in megavoltage photon beams using Monte Carlo simulations with the EGSnrc system. Two new techniques for the calculation of OAR profiles are presented. Results of the Monte Carlo simulations are compared to measurements performed in 6, 10 and 25 MV photon beams produced by an Elekta Precise linac and shown to agree within the experimental and simulation uncertainties. Comparisons with calculated in‐air kerma profiles demonstrate that using a plastic mini phantom gives more accurate air‐kerma measurements than using high‐ Z material buildup caps and that the variation of chamber response with distance from the central axis must be taken into account.