Dosimetry laboratories use reference ionization chambers (ICs) as their primary instruments for measuring radiation doses. The ICs are designed to have defined and accurate response characteristics, making them suitable for calibrating radiation detectors in specific beam qualities. This study assesses six ionization chambers (Radcal 10X6-3CT, Radcal 10X6-M, Radcal 10X6-10, Radcal 10X6-6, Exradin A4, and FC-65-G1) in standard International Electrotechnical Commission (IEC) defined diagnostic beams [RQR, RQA, RQT, and RQR-M (W + Al)] at the Secondary Standard Dosimetry Laboratory (SSDL). Calibration coefficients were estimated to evaluate energy dependency and relative response deviations of the ICs. Results showed that most ICs tested had limited energy dependency in RQR, RQA, and RQT beams, with deviations under 5%, confirming their suitability for clinical dosimetry and reference calibration at the SSDL. The Radcal 10X6-M performed well in mammography beams, while the other ICs showed significant deviations (6%–107%) in RQR-M (W + Al), limiting their mammography use. A key finding is the extended applicability of certain ICs beyond their specified energy ranges, particularly the Radcal 10X6-3CT, Radcal 10X6-M, and Radcal 10X6-10, which performed well in a broader range of diagnostic beam energies. This study provides essential data for optimizing IC selection and calibration, and highlights the need for further development of energy-independent ICs for enhanced versatility across clinical settings.
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