Detector correction factors in millimetre-scale fields
In plain words
In beams only a few millimetres wide the detector itself disturbs the radiation it is measuring. The corrections needed are large and not known precisely.
Precise statement
Determine field-output correction factors for active and passive detectors in photon fields of equivalent square side 2 to 20 mm, where lateral charged-particle equilibrium fails and source occlusion sets in, to a standard uncertainty below 1 percent. Required: detector-specific perturbation factors from Monte Carlo with validated geometry and from independent measurement. An answer is a correction-factor set with that uncertainty.
What would settle it
Agreement within 1 percent between independent Monte Carlo and primary-standard measurements, such as water calorimetry, in the same small fields.
Status in the literature
The IAEA and AAPM TRS-483 formalism of 2017 supplies factors, with residual uncertainty above 1 percent for the smallest fields and some detectors.