Modeling ion recombination in liquid ionization chambers — Improvement and analysis of the two‐dose‐rate method

Abstract

Due to the approximation used to separate initial and general recombination the valid range of collection efficiencies for the two-dose-rate method will not only depend on the model used to describe general recombination but also on the type of liquid and radiation beam quality. As there is no robust theory for initial recombination in liquids to apply, the valid range of general collection efficiencies for the two-dose-rate method should be experimentally evaluated for each radiation dosimetry application.

Monte Carlo calculated and experimentally determined output correction factors for small field detectors in Leksell Gamma Knife Perfexion beams

“…This was justified on the assumption of a negligible difference in recombination effects for the different field sizes used, expected to cancel out when ratios of detector readings are determined. Andersson (2013) investigated experimentally the general recombination in a LIC irradiated by continuous photon beams, finding that the collection efficiency decreased by 0.5% and 0.2% when the dose rate was changed from 2.2 Gy min −1 to 4.4 Gy min −1 for operating voltages of 300 V and 900 V, respectively. For LGK beams, where dose rates are within a range similar to those of Andersson, the difference in dose rate between the smallest and the largest collimator size is approximately 20%, justifying the assumption that the field size dependence of recombination effects is negligible in our measurements.…”