AAPM TG-61 report on kilovoltage X-ray dosimetry. II. Calibration procedures and correction factors

The AAPM protocol for kV X-ray beam dosimetry presents procedures for the calibration of clinical orthovoltage X-ray beams in terms of absorbed dose based on ionization chambers calibrated free-in-air in terms of air-kerma. Two procedures are recommended based on where the point of interest is located: (1) the "in-air method" for determination of absorbed dose at the surface of a phantom based on a measurement free-in-air; (2) the "in-phantom method" for determination of absorbed dose at a depth of 2 cm in water, based on an in-water measurement. The protocol recommends the calibration equipment, procedures, and formalisms. This paper reviews the background of the calibration procedures and the equipment (ionization chambers, phantoms). As well, the sources of the conversion and correction factor data with their uncertainties are explained. The consistency of the datasets is discussed.