AAPM protocol for 40-300 kV x-ray beam dosimetry in radiotherapy and radiobiology

The American Association of Physicists in Medicine (AAPM) presents a new protocol, developed by the Radiation Therapy Committee Task Group 61, fur reference dosimetry of low- and medium-energy x rays for radiotherapy and radiobiology (40kV less than or equal to tube potential less than or equal to 300 kV). It is based on ionization chambers calibrated in air in terms of air kerma. If the point of interest is at or close to the surface, one unified approach over the entire energy range shall be used to determine absorbed dose to water at the surface of a water phantom based on an in-air measurement (the in-air method), If the point of interest is at a depth, an in-water measurement at a depth of 2 cm shall be used for tube potentials greater than or equal to 100 kV (the in-phantom'' method). The in-phantom method is not recommended for tube potentials <100 kV. Guidelines are provided to determine the close at other points in water and the dose at the surface of other biological materials of interest. The protocol is based on an up-to-date data set of basic dosimetry parameters, which product: consistent dose values for the two methods recommended, Estimates of uncertainties on the final dose values are also presented. (C) 2001 American Association of Physicists in Medicine.