Optimization of proton radiation shielding using multilayer concrete-iron-polyethylene barriers: A PHITS Monte Carlo study

This study evaluates the effectiveness of multilayer shielding configurations in attenuating proton radiation and secondary particles using the PHITS Monte Carlo code. Proton beams with energies of 50–250 MeV were transported through single-layer concrete and multilayer combinations of concrete, iron (Fe), and polyethylene (PE). Compared with low-density concrete, a Concrete + Fe barrier reduced transmitted proton fluence by approximately three orders of magnitude at 100–150 MeV and by about one order of magnitude at 250 MeV, with statistical uncertainties below 1 %. No transmitted protons were detected for Fe-based multilayers at 50 MeV within the statistical sensitivity of the simulations. Incorporating a hydrogen-rich PE layer downstream of Fe further suppressed secondary neutron and photon fluence through moderation and capture effects. These results provide quantitative, dose-relevant guidance for the early-stage design of proton therapy room shielding using practical multilayer combinations of concrete, iron/steel, and PE.