Evaluating the effectiveness of concrete and metal shields in photoneutron reduction: A Monte Carlo study

Abstract: Introduction: Neutrons are produced when photons interact with parts of the accelerator, materials in the treatment room, or the patient's body. These neutrons have significant biological effects due to their high quality factor, potentially leading to secondary cancers. Material and method: A Monte Carlo simulation was conducted using the MCNPX code to model an Elekta Infinity linear accelerator operating at 18 MV. The accelerator was situated inside a bunker measuring 7.4* 5 m2. To study photoneutron production and the effectiveness of shielding, various concrete mixtures were applied to the walls of the maze and treatment room. Results: Regardless of the modifications, both photon and neutron fluence decreased substantially as the distance from the maze entrance increased. The fluence reduction was more pronounced between the maze entrance and center. The lowest equivalent neutron doses behind the treatment room door were observed when Ord-Lim concrete was used, while the highest doses occurred with Gal-Bar concrete. Conclusion: The configuration of concrete layers within the treatment room and maze walls is a key factor influencing the changes in neutron dose behind the treatment room door. These variations result from differences in concrete composition and the way neutrons are absorbed in different setups.