Premium
Measurement of the replacement correction factor for parallel‐plate chambers in electron fields
Author(s) -
Reft Chester S.,
Kuchnir Franca T.
Publication year - 1991
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 - 10.1118/1.596740
Subject(s) - dosimetry , electron , physics , photon , optics , atomic physics , nuclear physics , nuclear medicine , computational physics , medicine
When parallel‐plate chambers are used for dosimetry in electron fields, the AAPM dosimetry protocol recommends a value of 1.0 for the replacement correction factor, P repl,pp, E , until further data become available. Here, P repl,pp, E for five commercially available parallel‐plate chambers was measured as a function of electron energy from a nominal value of 5.5 to 22 MeV by comparison with a cylindrical chamber whose P repl,cyl, E was obtained from data in the protocol. Since this method is based on the concept of a constant value for N gas,pp , the energy and modality dependence of N gap,pp is also investigated for these chambers for Co‐60, 4‐, 6‐, 24‐MV photons and for 22‐MeV electrons. It is found that for three of the chambers P repl,pp, E is independent of energy, consistent with unity within one or two standard deviations (s.d.). For the fourth chamber P repl,pp, E is similarly consistent with one above 10 MeV, but decreases at lower energies, while for the fifth one it shows a systematic drop with decreasing energy.