Assessment of Decommissioning Cost of Proton Therapy Centers Depending on the Shielding Material in the Building Process

Radiotherapy using accelerated-protons has increasing potential in dealing with some tumors, and consequently, in the last decade proton-therapy centers have grown rapidly throughout the world. In these facilities, prompt radiation attenuation is essential to achieve legal dose limits, but not enough to develop efficient radiation protection. Activation of mechanical elements, ambient, and shielding, is another relevant issue linked to safety radiation protection conditions and to the future dismantling and management of radioactive materials produced along the operation. Induced radioactivity remains in the walls of centers for several years, even decades, after their closure, so a reliable inventory estimation, dependent on the choice of the shielding material, would be advisable in the early stages of projects. To estimate and reduce decommissioning costs, which involve a sensitive part of total investment, it is essential to study the complete cycle of life of the facility. Thus, the goal of this work has been to carry out a comparative analysis of the neutron activation in the shielding of proton centers, depending on the employed concrete, using Monte Carlo codes (MCNP6 and PHITS). The assessment cover four types of concrete: conventional (POR), high-density with magnetite (MAG), high-hydrogen-content (COL), and low activation (SLA). Considering the energy of neutrons, up to 230 MeV, several nuclear data and models were used. The optimal choice depends on attenuating prompt radiation below legal limits, reducing the exposure to gamma radiation of the staff, generating as little radioactive waste as possible and optimizing costs.