The influence of neutron contamination on pacemaker in photon beam radiotherapy by LINAC using the Monte Carlo method

  In radiation therapy with high-energy photon beams (E > 10 MV) neutrons are generated mainly in LINACs head thorough (γ,n) interactions. These neutrons affect the shielding requirements in radiation therapy rooms. According to the AAPMTG-34 report, photon absorbed dose of 10Gy can cause permanent damage to the pacemaker and the dose of 2Gy can make minor changes in the functioning of the pacemaker. So, in the radiotherapy of patients with pacemakers, the system should be designed to limit the dose of the pacemaker to 2Gy.In the current study, the Varian Clinac 2100C linear accelerator head and the pacemaker were fully simulated, the neutron and photon flux were evaluated by the FLUKA code. All components of the heart pacemaker, including battery and circuit parts, leads and connector were simulated according to real case. The results of the simulation were compared with measurements to verify the simulated model. Forthe treatment of prostate cancer where the pacemaker is located more than 40 cmfrom the treatment field, the neutron flux is observed in a wide range ofthermalneutrons tofast. Therefore, in addition to thetarget tissue that receives the highest unwanted neutron dose during treatment, close organs and, subsequently, other organs receive a considerable dose ofneutrons. The highest amount of flux on the surface of the titanium body of the pacemaker is for 100 keV photons and the most of the neutron flux is in the thermal region.The results of photon and neutron flux in the battery layers show that the maximum flux is in steel layer and then for lithium.