A comparison of semiempirical models for generating tungsten target x-ray spectra

Models for the computer generation of tungsten target x-ray spectra proposed by Birch and Marshall [Phys. Med. Biol. 24, 505-517 (1979)] and recently by Tucker, Barnes, and Chakraborty [Med. Phys. 18 211-218 (1991)] are compared. Some basic differences in the equations for the number of bremsstrahlung photons of different energies in the spectra are discussed. The models are compared in terms of their ability to characterize x-ray spectra from constant potential clinical units using three parameter equivalent spectra (EQSPEC) determined from the fit of model generated transmission curves through aluminum to measured data. The Kramers model for x-ray generation is included for completeness. It is shown that two of the models generate very similar x-ray spectra from given transmission curves although the fitting parameters in the EQSPEC characterization differ.