Perturbation correction factors for some ionization chambers commonly applied in electron beams

Abstract

Values for the fluence perturbation correction factor were determined in a number of electron beams for the commonly applied PTW/Markus plane-parallel chamber and the cylindrical NE 2571 Farmer chamber. These data were determined relative to the NACP plane-parallel chamber as a function of the mean energy at depth, E_z, calculated according to the method recommended in modern dosimetry protocols. For the cylindrical chamber the results are in agreement with the data recommended in these protocols. For the PTW/Markus chamber a small but significant fluence perturbation correction is necessary: up to about 3% for a value of E_z=2 MeV. In order to check the value of these fluence perturbation correction values, dose measurements were performed ionometrically and compared with values determined with the Fricke dosimetry system.