Obtaining the intrinsic electron spectrum of linear accelerators using the relation between the current of the bending magnet and the absorbed dose in water

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 R50 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.