Photoneutron measurement and shielding in radiotheraphy

Objective: In radiation therapy of cancer patients, high energy X-rays are used which are produced by linear accelerators. If the energy of these beams are over 8 MeV, they interact with metallic parts of the linear acceleator. This incident is called photonuclear reaction, as a result of these interactions, neutrons are also produced as secondary radiation products (γ,n). These neutrons are called photoneutrons. To prevent radiation damage from photoneutrons of the workers and the environment, the photoneutron flux and dose must be determined. The purpose of this study, the detection of photoneutron neutron flux consisting in the linear accelerators room and the determination of appropriate shielding materials and the development for this flux. Method: Photoneutron flux detection and testing of the neutron shielding neutron activation analysis method is used. Measurements made at different positions in the Philips SLI-25 linear accelerator treatment room and location-based distribution of thermal neutron flux are obtained. Measurements taken with AMATEM-ORTEC brand GMX-20195-P model n-type high purity germanium (HPGe) detector and GF3 spectrum analyzer program was used. Results: Maximum thermal neutron flux in the treatment room was found in the direction of G on the top of the linac head. Neutron flux 92% decrease to the walls, just in front of the linac door maximum neutron flux less than 1%. The shielding percentage of same neutron flux of the neutron shielding material; 5% boron doped polyethylene 89-90%, 10% boron doped paraffin 86%, high density polyethylene 64%, paraffin 62%, polyethylene 59%, polypropylene 58%, cast polyamide 53%. Conclusion: Linear accelerators photoneutron flux in the room, may lead the way for additional studies of neutron dose to the patient. Produced a 10% boron doped paraffin with the development of more effective and less costly shielding material can be manufactured neutron shield.