Objective.To experimentally determine beam quality correction factors (kQ) for six cylindrical and four parallel-plate ionization chambers in both spread-out Bragg peak (SOBP) and single-layer proton beam configurations.Approach.Water calorimetry was implemented to establish absorbed dose to water (Dw) at 10 g cm-2 depth for SOBP and single-layer proton beams. Ionization chamber 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 60CoDwstandard at the National Institute of Metrology (NIM) to obtainDwcalibration coefficients (ND,w). ThekQ values were determined through integrated water calorimetry and ionization chamber measurements.Main Results.The relative standard uncertainties inDw determination were quantified as 0.43% for SOBP beams and 0.51% for single-layer beams. The experimentally determinedkQ values demonstrated agreement with both TRS-398 reference data and published literature within declared measurement uncertainties.Significance.This work presents the first comprehensive determination ofkQfactors for SOBP and single-layer proton beams using water calorimetry. The obtainedkQvalues with reduced uncertainties (0.56-0.63%) establish metrological traceability for ten clinical ionization chamber models, directly enhancing the accuracy of scanned proton beam dosimetry in radiotherapy practice.
Keywords: absorbed dose to water; beam quality correction factor; ionization chamber; scanned proton beams; water calorimetry.
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