Water calorimetry-based determination of absorbed dose to water and beam quality correction factors for ten ionization chambers in scanned proton beams

Abstract Objective. To experimentally determine beam quality correction factors ( k Q ) for six cylindrical and four parallel-plate ionization chambers (ICs) in both spread-out Bragg peak (SOBP) and single-layer proton beam configurations. Approach. Water calorimetry was implemented to establish absorbed dose to water ( D w ) at 10 g cm −2 depth for SOBP and single-layer proton beams. IC measurements were performed under identical geometrical conditions as calorimetric measurements, with the exception of water temperature control in the phantom. Systematic evaluation of ion recombination and polarity effects was achieved through sequential measurements at operational voltages of −400 V, −300 V, −200 V, −150 V, and +400 V in scanned proton beams. All chambers were calibrated against the 60 Co D w standard at the National Institute of Metrology to obtain D w calibration coefficients ( N D ,w ). The k Q values were determined through integrated water calorimetry and IC measurements. Main results. The relative standard uncertainties in D w determination were quantified as 0.43% for SOBP beams and 0.51% for single-layer beams. The experimentally determined k Q values demonstrated agreement with both TRS-398 reference data and published literature within declared measurement uncertainties. Significance. This work presents the first comprehensive determination of k Q factors for SOBP and single-layer proton beams using water calorimetry. The obtained k Q values with reduced uncertainties (0.56%–0.63%) establish metrological traceability for ten clinical IC models, directly enhancing the accuracy of scanned proton beam dosimetry in radiotherapy practice.