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Ionization chamber, electrometer, linear accelerator, field size, and energy dependence of the polarity effect in electron dosimetry
Author(s) -
Ramsey Chester R.,
Spencer Kelly M.,
Oliver Adrian L.
Publication year - 1999
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 - 10.1118/1.598507
Subject(s) - electrometer , ionization chamber , dosimetry , linear particle accelerator , polarity (international relations) , calibration , ionization , physics , computational physics , field (mathematics) , atomic physics , particle accelerator , electron , optics , ion , nuclear physics , chemistry , beam (structure) , nuclear medicine , mathematics , medicine , biochemistry , quantum mechanics , pure mathematics , cell
Plane‐parallel ionization chambers are the instrument of choice for use in electron calibration and dosimetry, but these chambers may exhibit large polarity effects. This study concentrates on measuring the dependence of the polarity error at various mean energies using different linear accelerator, field size, ion chamber, and electrometer combinations. The polarity error was shown to increase for all four ionization chambers as the mean energy at depth decreased, but was always less than one percent at d max . Polarity error dependence was also observed for similar plane‐parallel chambers, varying field sizes, and different linear accelerators, but no polarity error dependence was observed for similar cylindrical chambers and different electrometers. Measurements of the polarity error can be used to develop correction factors for future measurements that will help minimize the time spent performing electron dosimetry and calibrations. These correction factors can be used to calculate the correct reading without the need to reverse the chamber bias, thus reducing the number of measurements required.