On the Use of Roentgen-Calibrated, Cavity-Ionization Chambers in Tissue-like Phantoms to determine Absorbed Dose

Abstract

Roentgen-calibrated cavity-ionization chambers are used to determine point absorbed dose in a tissue-like phantom. A calibration factor for 2 MV x-rays includes corrections for wall attenuation of the chamber, for any lack of electronic equilibrium, and for the stopping power of the wall material relative to air. A further correction is required to determine the exposure dose that would have been obtained at the point in the absence of the chamber and any wall-thickening cap used in the calibration. The correction factor required to compensate for the attenuation of the phantom material removed to accommodate the chamber and its cap can be determined from experimental data already available. A rad/ roentgen conversion factor for 2 MV x-rays and a water phantom is calculated.