Poster - Thur Eve - 67: Variations in Ion Chamber Response for Low- and Medium-Energy X-Rays

Abstract

The sensitivity of different models of ionization chambers used in radiation therapy varies substantially over the low‐ and medium‐energy x‐ray qualities in the effective energy (Eeff) range of 20 – 160 keV. Previous authors calculated some of these variations for 4 common models of ion chambers using EGSnrc Monte Carlo (MC) techniques1, but lacked sufficient experimental data to demonstrate the accuracy of their calculations. This work presents sets of measured calibration coefficients from a substantial number of each of 6 common models of ion chambers over this effective energy range. Measurements are based on calibrations performed with the primary standard beams at the X‐ray calibration laboratory of Ionizing Radiation Standards at NRC. This data demonstrates the degree that the response of commercially manufactured ion chambers varies between different models of chamber. In general, identical models follow the same shape of response curve over low‐ and medium‐energy x‐ray qualities in the Eeff range of 20 – 160 keV. The general shape of the response curves for this energy range can be accurately modeled with EGSnrc.