A dose calibrator usually consists of a well-type ionisation chamber filled with pressurised gas. When a radioactive sample is placed inside the chamber, emitted photons interact with the gas and produce ionisation.

The resulting electrical current is proportional to the radiation intensity, which is then converted into activity (e.g. MBq) using calibration factors specific to each radionuclide.

Several factors influence accurate measurement:

• Photon energy

• Detector geometry

• Sample volume and container type

• Radionuclide-specific calibration settings

Because the ionisation chamber measures radiation indirectly, calibration settings must be correctly selected for the radionuclide being measured.

Quality control testing typically includes:

Constancy testing (daily) to confirm stable readings using a long-lived reference source.

Linearity testing (periodic) to ensure accurate measurement across a range of activities, particularly high activities used in therapy.

Accuracy testing to verify correct calibration against a known standard source.

Geometry testing to confirm that measurement is not significantly affected by sample volume or container configuration.

If a dose calibrator is inaccurate, patients may receive too little activity (non-diagnostic images) or excessive activity (unnecessary radiation exposure).

Cross-calibration between the dose calibrator and imaging system is also essential for quantitative PET imaging and SUV accuracy.