Abstract
BACKGROUND: Existing calibration procedures of ionization chambers refer to the cobalt 60 ((60)Co) beam and require a k (Q) quality conversion factor for therapeutic photon beams. This factor has the largest contribution to the total standard uncertainty of dose measurement. The main objective of our work is to verify the performance of the experimental DW2 ionization chamber for the absorbed dose to water measurements using Monte Carlo (MC) calculations instead of calibration in the Secondary Standard Dosimetry Laboratory (SSDL). MATERIALS AND METHODS: To calculate the absorbed dose to water based on the signal from the experimental DW2 ionization chamber, its active volume was determined. Using experimental methods, the correction factors for polarisation and ion recombination were established. Additionally, MC methods were employed to determine the factors for converting the ionization charge in the chamber cavity to the absorbed dose to water. Subsequently, the chamber's performance was verified against ionometric and calorimetric Central Office of Measures (GUM) standards under reference conditions. RESULTS: The difference between the dose measured by the DW2 chamber and the GUM ionometric standard for the (60)Co beam was -0.09%. The differences for the 6, 10 and 15 MV photon beams relative to the graphite calorimeter were -0.30%, 0.40%, and 0.45%, respectively. The maximum expanded (k = 2) standard uncertainty of the chamber was 0.57%. CONCLUSIONS: This work demonstrates that it is possible to obtain accurate measurements of the absorbed dose to water for high-energy photon beams under reference conditions using an ionization chamber without calibrating it in a (60)Co source but only using correction factors determined by MC calculations.