Evaluation and measurement of the secondary neutron dose in high energy X-ray radiotherapy at the Ayatollah Khansari hospital

Medical linear accelerators (linacs) are used efficiently in radiation therapy for tumor treatments. In these devices interaction of high energy photons (greater than 7 MeV) with the target, flattening filters, collimators and even body and patients bed produce secondary particles such as neutrons(photo-neutron production). The purpose of this study is measuring the neutrons dose produced in medical linear accelerator Elekta Precise by using monte carlo code MCNPX simulation and comparing them with the experimental results of the TLD-600 and TLD-700 dosimeters The results show that for the TLDs located exactly below the gantry and on the bed (TLD 1), the thermal neutrons dose proportion to the dose of photons incident in simulation calculations is 0.2%, where the experimental value is 0.21% . The discrepancy between the experimental results and the calculation is around 4%, which shows a good agreement.