Estimation of neutron and gamma radiation doses inside the concrete shield wall for 10 and 15 MV medical linear accelerators

High-energy electron linear accelerators (linacs) are used in radiotherapy for tumor treatment. By operating at electron energies above the thresholds of the (γ, n) photonuclear reaction, undesirable photoneutrons and radioisotopes are generated by high-energy x-rays. These photonuclear reactions occur on the linac accelerator head components, which are made from various materials. In these reactions, one can assume that secondary neutrons are dispersed all over the treatment rooms. The present work observed ambient dose equivalent of photon and neutron, and number of etch pits of wide-energy range Neupit produced by thermal and fast neutrons inside a model of iron shielding wall. The neutron dose around the surface of the shielding wall was detected less than three orders of magnitude of photons at 10 MV linac. The total neutron dose in a 15 MV linac was about one order higher than that in the 10 MV linac. In addition, the 15 MV linac incident photons clearly generated secondary neutrons inside the iron shielding wall. (author)