Ionization chamber dosimetry at a linear acceleration used for radiation therapy: analysis of dose deviations stemming from the use of different dosimetry concepts

At a linear accelerator used for medical purposes, a cylindrical and a flat ionization chamber, respectively, were calibrated using the procedures: (1) Water energy (deposition) calibration, (2) Standard ion dose (=air) calibration, (3) Markus chamber calibration, all with regard to water energy dose which is the relevant quantity for radiation therapy planning. The primary accelerator energy range was 4-25 meV, and depth dependent dose rates for photons and electrons were considered. The aim is the comparison of water energy doses obtained by the three calibration methods, and an estimate of the resulting uncertainty of each, which turns out to be about 5%. (Quittner)