Calibration of X-ray multimeters for radiography

Accurate determination of air kerma, tube‑voltage‑related quantities (TV), and half‑value layer (HVL) is essential for reliable dosimetry in X‑ray imaging. X‑ray multimeters (XMMs) are widely used for these measurements; however, their performance depends on spectral characteristics and measurement conditions. This study evaluates the consistency and clinical applicability of calibration coefficients derived using industrial and clinical X‑ray systems across a range of clinically relevant radiation qualities.

Eight XMMs from four manufacturers were calibrated for air kerma, TV, and HVL using one laboratory and three clinical systems. Reference values were established using traceable ionization chambers, high voltage dividers, and spectrometry. Calibration coefficients were assessed for standard aluminium filtered radiation qualities and for an extended range including 0-0.9 mm of copper filtration. Energy dependence, X‑ray system dependence, and the impact of applying calibration coefficients were evaluated.

For air kerma, calibration coefficients derived using industrial and clinical systems were highly consistent. Energy dependence variations were within 5% and could be reduced to below 1% by applying radiation‑quality‑specific calibration coefficients. TV measurements showed the strongest dependence on the X‑ray system; energy dependence variations were generally below 4% and could be improved only using clinical‑system‑based calibrations. For HVL measurements, energy dependence variations were typically within 6% and were reduced below 1% by calibration, except for two XMMs exhibiting system‑dependent behaviour.

XMMs can provide reliable measurements across clinically relevant radiation qualities, including copper‑filtered beams, when radiation‑quality‑specific calibration coefficients are applied. Interpolation based on a single radiation quality parameter is insufficient; at least two parameters are required.