Development of the spectrum reconstruction method for bremsstrahlung beams with different field sizes, created medical electron linear accelerators (LAE), on the base of the deep dose distributions in a water phantom and determination of photon spectra for Varian Trilogy accelerator 6 MV. The proposed methodology is based on the use of dose kernels algorithm of point monoenergetic monodirectional source (pencil beam (PB)) for the depth dose distribution calculation, created different cross-section beams of in a water phantom, and experimental measurements of these distributions. For solving the inverse problem is applied Toolbox routines ’Optimtool’ knowing mathematical package MATLAB to solve. Bremsstrahlung energy spectrum generated medical accelerator Varian Triology with different sizes of square fields from 3 x 3 up to 40 x 40 cm2 and average energy photons, depending on the size of the fields were received. Dose kernels for a set of defined energies PB were calculated. Depth dose distribution in a water phantom, calculated using the obtained spectra and dose kernels agree well with measurement dose distributions. The proposed technique reconstruction of bremsstrahlung spectrum of medical accelerator is good adequate. Average energy spectra of photons for Varian Trilogy Accelerator in regime 6 MV varies from 1.71 to 1.43 MeV depending on the field size.
Keywords: radiation therapy, medical accelerators, bremsstrahlung, reconstruction of the photon spectrum.