Evaluation of water equivalent ratio (WER) values for polyethylene, polymethyl methacrylate, polystyrene, lead, tungsten and aluminum at helium ion energies ranging from 25-250 MeV/u through Monte Carlo simulation

Background: There is no data concerning water equivalent ratio (WER) values for helium ion beams in an extensive range of energies as well as relevant dosimetric materials. Materials and Methods: In this work, quantities related to depth-dose profiles and WER values were evaluated in water, Polyethylene (PE), Polymethyl Methacrylate (PMMA), Polystyrene (PS), Lead (Pb), Tungsten (W) and Aluminum (Al) for helium ion energies ranging from 25-250 MeV/u using MCNPX 2.4.0 Monte Carlo code. Results: For all the studied energy range, the mean values of WER for PMMA, PE, PS, Pb, W and Al were 1.161, 0.995, 1.049, 5.421, 9.512 and 2.091, respectively. Among the studied materials, PE and W showed the least and most difference to water, respectively. Also the WER values of some of the studied materials for helium ion beams were compared with the same materials for proton beam. Conclusion: The evaluated WER values were in acceptable accordance with the data reported in the literature by less than 2.6 % difference. Also, WER values of the mentioned materials for helium ions and protons have been compared and it was concluded that dose characteristics of PE are the most similar to water in the field of both helium ions and proton beams.