Optimal design for the renovation of a medical linear accelerator room into a cyclotron room

In response to the development needs of nuclear medicine, this study proposes a solution to convert a linear accelerator into a cyclotron room. Through theoretical calculations and MCNP (Monte Carlo N-particle transport code) simulations, we evaluated the shielding effectiveness of the original heavy-concrete structure (1.2–2.6 m thick) against γ-rays, and proposed an optimized scheme that adds boron-containing polyethylene (24–48 cm) to the inner walls for neutron shielding. The results show that the original concrete structure meets the requirements for γ-ray protection. Simulations verify that selecting boron-containing polyethylene provides high neutron-shielding efficiency with a smaller increase in secondary γ radiation, resulting in lower dose rates. By combining a polyethylene moderator layer with an 11% boron-containing polyethylene absorption layer, the risk of neutron activation from iron-ore aggregates is effectively avoided. This solution involves low construction difficulty and controllable costs, and enables efficient reuse of medical facilities. The study provides technical guidance for similar renovations and supports policy goals for the high-quality development of nuclear medicine in China.