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How accurately can EGS4/PRESTA calculate ion‐chamber response?
Author(s) -
Rogers D. W. O.
Publication year - 1993
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 - 10.1118/1.597071
Subject(s) - ionization chamber , dosimetry , ion , physics , nuclear medicine , medical physics , medicine , ionization , quantum mechanics
Ion‐chamber responses are calculated for graphite, PMMA, and aluminum‐walled ion chambers free‐in‐air in 60 Co beams and 200‐keV beams for a graphite chamber. The EGS4 Monte Carlo system is used with various electron step‐size algorithms, in particular the PRESTA algorithm, the much simpler ESTEPE constraint on the energy loss per step, and in combination. Contrary to previous reports, it is found that there are variations in the calculated ion chamber response of up to 3% in 60 Co beams and up to 8% in the 200‐keV beam. It is recommended that all ion chamber calculations be done with the PRESTA algorithm plus an additional constraint on the energy losses per step of 1% (or less for higher‐ Z materials). The systematic uncertainty in the calculations for 60 Co beams is found to be 1% (1σ) and somewhat higher in 200‐keV beams because of sensitivity to transport parameters such as AE and ECUT.