Purpose: To present a novel methodology to model the intrinsic electron spectra of a linear accelerator and its situation with respect to the energy window.
Methods: The spectra are obtained by fitting the variation of R(50) and the maximum dose rate measured in a water phantom with the bending magnet current. The obtained spectra are verified with a realistic Monte Carlo simulation of the accelerator.
Results: The intrinsic spectra and their relative position with respect to the energy window of the bending magnet have been obtained for a Siemens Mevatron KDS and an ELEKTA SL20 accelerators.
Conclusions: Using this method in the commissioning and scheduled revisions of the accelerator, the tuning of the current of the bending magnet could be done in such a way that both the quality of the beam and the dose rate would reach a better long-term stability.