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Technical Note: On the use of cylindrical ionization chambers for electron beam reference dosimetry
Author(s) -
Muir Bryan R.,
McEwen Malcolm R.
Publication year - 2017
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 - 10.1002/mp.12582
Subject(s) - dosimetry , ionization chamber , ionization , imaging phantom , electron , cathode ray , physics , atomic physics , beam (structure) , range (aeronautics) , ion , optics , computational physics , materials science , nuclear physics , nuclear medicine , composite material , medicine , quantum mechanics
Purpose To investigate the use of cylindrical chambers for electron beam dosimetry independent of energy by studying the variability of relative ion chamber perturbation corrections, one of the main concerns for electron beam dosimetry with cylindrical chambers. Methods Measurements are made with sets of cylindrical and plane‐parallel reference‐class chambers as a function of depth in water in 8 MeV and 18 MeV electron beams. The ratio of chamber readings for similar chambers is normalized in a high‐energy electron beam and can be thought of as relative perturbation corrections. Data are plotted as a function of mean electron energy at depth for a range of depths close to the phantom surface to R 80 , the depth at which the ionization falls to 80% of its maximum value. Additional, similar measurements are made in a Virtual Water® phantom with cylindrical chambers at the reference depth in a 4 MeV electron beam. Results The variability of relative ion chamber perturbation corrections for nominally identical cylindrical Farmer‐type chambers is found to be less than 0.4%, no worse than plane‐parallel chambers with similar specifications. Conclusions This work discusses several issues related to the use of plane‐parallel ion chambers and suggests that reference‐class cylindrical chambers may be appropriate for reference dosimetry of all electron beams. This would simplify the reference dosimetry procedure and improve accuracy of beam calibration.