A comparative evaluation of calibration methods for a multilayer ionization chamber

Abstract The uniformity calibration of a multilayer ionization chamber (MLIC) is crucial for ensuring the quality of depth dose distribution measurement and a comparative evaluation in the performance of calibration methods is lacking. In this study, we developed an MLIC and the mean water-equivalent length (WEL) of each layer was determined. The calibration coefficients of this MLIC were obtained through three different calibration methods and were used to correct the raw data of five energies. Measurements demonstrated high repeatability (average relative standard deviation ≤ 1.0% across all channels) for two key characteristic parameters of integrated depth dose (IDD): R 80 , defined as the depth at which the dose falls off to 80% of its maximum value, and dose distal fall-off (DDF), defined as the distance between the distal 80% and 20% of the maximum dose. The short-term stability of these parameters was within ± 0.01 mm for R 80 and ± 0.001 mm for DDF, respectively. These three calibration methods showed insignificant contributions in reducing differences between R 80 and DDF values measured by the MLIC and their reference values in water. Across all five energies examined, the average relative deviations achieved with a so-called “shifted board” method, water phantom method and penetration method are 9.78%, 16.72%, and 15.55%, respectively. The shifted board method demonstrates superior agreement with reference profiles measured in a water phantom, surpassing the other two calibration methods.