Photoneutron Contamination Evaluation in High-Energy Medical Linac in Radiotherapy Facility

High-energy medical linear accelerators operating above 8 MV are known to produce photoneutrons, which contribute to additional radiation exposure for both patients and clinical staff. Research in this area commonly involves evaluating photoneutron contamination and characterizing neutron spectra using advanced Monte Carlo simulation codes such as PHITS. Typical investigations include validating photon beam characteristics, analysing neutron energy distributions, and assessing neutron dose equivalent H*(10) across various field sizes and depths within a phantom. Fast neutrons are generally dominant at the source but undergo significant moderation in tissue-equivalent materials. Results often show a peak neutron dose around intermediate field sizes and a consistent decrease with depth, with variations observed when compared across different simulation platforms due to differences in nuclear data libraries and conversion methodologies. Overall, these studies reinforce the importance of accounting for photoneutron production in high-energy radiotherapy environments and highlight the need for continued benchmarking, cross-code comparisons, and experimental activation studies to refine radiation protection assessments.