KEY POINTS
- Four commercially available X-ray multimeters were evaluated at the International Atomic Energy Agency dosimetry laboratory: the Barracuda R100B, Black Piranha, Nomex Multimeter and X2 MAM detector.
- Calibrations were performed for molybdenum/molybdenum and tungsten/aluminium spectra at 25, 28, 30 and 35 kV. Polymethyl methacrylate sheets of 1.986, 2.775 and 4.761 mm were placed close to the tube to modify the primary spectrum while limiting scatter at the detector.
- Calibration coefficients for air-kerma rate, half-value layer and tube voltage were determined by substitution against traceable reference instrumentation. Each multimeter reading was averaged across three ten-second exposures under identical geometry.
- Additional polymethyl methacrylate increased the measured half-value layer by as much as 46% for tungsten/aluminium and 28% for molybdenum/molybdenum. At 35 kV, the tungsten/aluminium half-value layer increased from 0.42 to 0.61 mm aluminium.
- Relative to calibration without additional polymethyl methacrylate, calibration coefficients changed by up to 11% for air-kerma rate, 37% for half-value layer and 42% for tube voltage, despite unchanged nominal anode, filter and tube-voltage settings.
- The X2 showed the greatest stability against spectral change, although tube-voltage deviations still reached approximately 10%. The Black Piranha showed particularly pronounced sensitivity to spectral mismatch.
- Software options also limited transferability. For example, the Nomex offered only a tungsten/0.7 mm aluminium selection and therefore could not be evaluated for the study’s tungsten/0.5 mm aluminium spectrum; compression-paddle settings were tested where available.
CLINICAL TAKEAWAY
Calibration coefficients derived from nominally similar mammography spectra should not be assumed to remain valid after changes in filtration, compression-paddle configuration or beam geometry. Multimeters should be validated under conditions representative of their actual clinical use, particularly when half-value layer or tube voltage is used for dose calculation and quality-control decisions.