Performance of air kerma - area product meters based on long-term calibration data

Kerma-area product (KAP) meters are widely used to monitor patient radiation exposure in medical X‑ray imaging. To ensure the reliability and comparability of KAP data, traceable calibration is essential. The required radiation‑quality coverage and calibration interval depend on the target measurement uncertainty.

In this study, long‑term calibration data collected over an eight‑year period were analysed to assess the stability, air‑pressure dependence, and energy dependence of KAP meter response. The performance of 28 KAP meters was evaluated, and all instruments met the requirements of the current International Electrotechnical Commission standard IEC 60580:2019. The study extended beyond the IEC 61267:2005 RQR radiation qualities by also including a wider range of clinically relevant beam qualities generated using 0.1-0.9 mm of added copper filtration.

All KAP meters demonstrated compliance with the IEC limit of ± 2 % per year for reference‑class instruments, and no correlation between response variations and air‑pressure conditions was observed. However, the energy dependence of response did not always meet the ± 8 % criterion for RQR radiation qualities, with deviations of up to 25 % observed. When the radiation‑quality range was extended using copper filtration, the variation increased to as much as 60 %.

These findings highlight the importance of traceable calibration for KAP meters. It is recommended that the full clinically relevant range of radiation qualities be covered during commissioning. Due to the demonstrated long‑term stability of the meters, the number of calibration points may be reduced in subsequent periodic calibrations.