Assessment of compact cylindrical and plane-parallel ionization chambers as reference dosimeters in high-energy...

To assess the performance of compact cylindrical and plane-parallel ionization chambers that are currently not included in international dosimetry protocols in high-energy photon beams, and evaluate their suitability as reference chambers.

Four types of cylindrical (IBA RAZOR^TM Nano, CC01, CC04, CC08) and two types of plane-parallel (PPC40, PPC05) chambers were investigated. Measurements were performed for five photon beams with TPR_20,10 values ranging from 0.680 to 0.764. Polarity, recombination and beam quality correction factors (k_Q) were determined for all chamber types across all beam qualities. The k_Q-factors were obtained by direct calibration against a water calorimeter. Chamber stability was evaluated based on available long-term calibration coefficients.

The experimentally determined k_Q -factors exhibited a standard uncertainty (k = 1) between 1.1% and 1.5%, with the largest sources of uncertainty stemming from the heat transfer within the calorimeter vessel and the chamber calibration coefficients. Results were consistent within 0.2% for chambers of the same type. Comparison with literature data from experiments and Monte Carlo simulations demonstrated strong agreement for all chambers except the CC01, where discrepancies are likely due to the presence of a steel electrode. Polarity and recombination correction factors were small and stable across all investigated beam qualities. Cylindrical chambers showed good stability, with somewhat larger variations observed for plane-parallel chambers.

This work expands the database of available k_Q-factors for ionization chambers not currently included in dosimetry protocols and provides experimental data on their behavior in high-energy photon beams, contributing to their evaluation for use in reference dosimetry.