Estimating the relative biological effectiveness of light ions using TOPAS monte carlo simulation.

Background: This paper presents a Monte Carlo (MC) simulation study estimating Relative Biological Effectiveness at a 10% survival fraction (RBE10) of light ion beams by means of microdosimetric approach. Microdosimetric parameters for estimating Relative Biological Effectiveness (RBE) were determined through the utilisation of the Tool for Particle Simulation (TOPAS) MC simulations. These simulations incorporated a 3D silicon on insulator (SOI) Bridge microdosimeter model. Materials and Methods: The incident 176.8 MeV proton and 176.4 MeV/u helium ion beams were simulated at different depths within a water phantom. The microdosimetric aspects, such as YF and YD at different depths along the fields were predicted from simulations. The RBE10 were derived using simulated microdosimetric spectra as inputs to the modified Microdosimetric Kinetic Model (MKM). Results: Simulated YD distributions for proton and helium ion beams in water were about 4 keV/µm and 4 to 8 keV/µm at the plateau region, respectively and around 7 to 14 keV/µm and 35 to 56 keV/µm at the Bragg peak (BP) region, respectively. In the tail region YD values were increasing from 5 keV/µm to 10 keV/µm and 7 keV/µm to 14 keV/µm at depths of 224 mm to 250 mm, respectively. Conclusion: The RBE10 for protons exhibit a range of 0.99 to 1.22, which differs from the standard practice of using a fixed RBE of 1.1 in the Treatment Planning System (TPS) for proton therapy. The simulation results in this study may be used as an outlook for radiobiological experiments in the NASA Space Radiation Laboratory (NSRL). [ABSTRACT FROM AUTHOR]