Purpose: To present a comprehensive shielding design for the first carbon-ion hybrid-synchrotron facility in the US.
Methods: The Integrated Oncology Building (IOB) will be the home of the first carbon/proton hybrid therapy system by the Hitachi, Ltd. It will provide proton beams up to kinetic energies of 230 MeV and carbon beams up to 430 MeV/n for clinical treatment. To provide adequate radiation protection, the Geant4 (v10.6) Monte Carlo toolkit was utilized to quantify the ambient dose equivalent at a 10 mm depth (H*(10) for photons and neutrons. The scoring ICRU soft tissue sphere was 30 cm in diameter. 3D computer-aided design files of the entire planned facility were imported into Geant4 using the STL format. Furthermore, various beamline and system components (bending magnets, FFC, gantry, to name a few) were imported into Geant4 to simulate realistic neutron interactions and self-shielding effects. The Glauber Griboy (GG) model was chosen to determine the elastic and inelastic cross-sections. For inelastic interactions, the conservative Bertini cascade model was chosen to model the secondary particle interactions.
Results: We have optimized each shielding slab thickness through iterative processes with more than 20 CAD file designs. The 430 MeV/n carbon beams play the most significant role in concrete thickness calculation. The primary wall thickness for the carbon fixed beam room is 4 meters. Most noticeably, the presence of the proton gantries caused the ambient dose equivalent to increase by around 70% at the maze entrance, but a decrease in the HEBT corridor. All shielding primary and secondary goals were met per state regulation and NCRP guidelines.
Conclusion: Leveraging 3D architectural renderings, particle therapy system components, and Geat4 Monte Carlo simulation techniques, the IOB facility meets all shielding goals mandated by the state regulations for clinical operations in 2025.