Study of the RBE depth dependence of protons using a damage diagnostic algorithm and its application in proton therapy based on Monte Carlo simulation

The present study aimed to calculate the yields of DNA breaks and the variation of relative biological effectiveness (RBE) at different depths for protons using Geant4-DNA. For this purpose, an atomic model of DNA and a DNA damage classification matrix were used to calculate different DNA break yields for 62-MeV protons. As the reference radiation, the secondary electron spectrum produced by Co-60 was evaluated. This helped to calculate the SSB and DSB yields. Moreover, RBE was found to be between 1.1 at the first point and 1.51 in the Bragg peak region. In this region, it was 37% greater than the 5-mm depth in the plateau region. Considering different threshold energies, the energy deposition at 10.79 eV had the most contribution to the total damage. As the results suggested, the depth dependence of RBE should be taken into account for proton therapy. It was also found that DNA break yields significantly depend on the threshold energy value.