Characterisation of a megavoltage linear accelerator Bremsstrahlung by means of Monte Carlo simulations

Abstract

This work presents a method for megavoltage X-ray Bremsstrahlung assessment by means of Monte Carlo (MC) (PENELOPE) simulations. The proposed method provides suitable spectrum characterisation by means of a few parameters, namely the acceleration potential and incident angle of electron beam on the anode. The obtained spectra have been used as incident beam for in-depth dose distribution determination with the aim of performing further comparisons with experimental data. This comparison procedure has been employed for Bremsstrahlung assessment optimisation. Once the Linac Bremsstrahlung is well established, it may be used as incident beam for further dosimetric purposes, such as spatial dose distribution calculations.The whole process has been applied for the characterisation of the megavoltage Bremsstrahlung from a typical Linac, namely the 10 MV Varian Clinac 18. The obtained results for in-depth dose distributions, when compared with experimental measurements, show an overall good agreement, which may suggest the feasibility of the method. Results and DiscussionBremsstrahlung assessment: spectral and angular distributionsThe first approach consisted on the comparison of the different theoretical and semi-empirical Bremsstrahlung models described earlier. Actually, it is expected that when β tends to unity, the scattering angular distribution would concentrate at forward directions.