A parameterization of the electron beam output factors of a 25-MeV linear accelerator

A new parameterization of the output factors of an electron beam has been developed. The output factors for the electron beams of an AECL Therac-25 have been determined for a variety of square and rectangular fields using ionization measurements and thermoluminescent dosimetry. The data were then least-squares fit by a semiempirical equation which treats the two field dimensions as variables. Such a parameterization allows computer-generated tables of output factors to be manufactured. The calculated values agree with the measured data in most cases to within the +/- 1% experimental uncertainty. A comparison between this method of calculating output factors and two conventional methods is also presented.