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 pr otocol, developed by the Radiation Therapy Committee Task Group 61, fur ref erence dosimetry of low- and medium-energy x rays for radiotherapy and radi obiology (40kV less than or equal to tube potential less than or equal to 3 00 kV). It is based on ionization chambers calibrated in air in terms of ai r kerma. If the point of interest is at or close to the surface, one unifie d 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 measure ment (the "in-air" method), If the point of interest is at a depth, an in-w ater measurement at a depth of 2 cm shall be used for tube potentials great er than or equal to 100 kV (the "in-phantom'' method). The in-phantom metho d is not recommended for tube potentials <100 kV. Guidelines are provided t o 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-t o-date data set of basic dosimetry parameters, which product: consistent do se values for the two methods recommended, Estimates of uncertainties on th e final dose values are also presented. (C) 2001 American Association of Ph ysicists in Medicine.