MEASUREMENTS OF THE PARASITIC NEUTRON DOSE AT ORGANS FROM MEDICAL LINACS AT DIFFERENT ENERGIES BY USING BUBBLE DETECTORS

Conventional linear accelerators (LINACs) for radiotherapy produce fast secondary neutrons due to photonuclear processes. The neutron presence is considered as an extra undesired dose during the radiotherapy treatment, which could cause secondary radio-induced tumors and malfunctions to cardiological implantable devices. It is thus important to measure the neutron dose contribution to patients during radiotherapy, not only at high-energy LINACs, but also at lower energies, near the giant dipole resonance reaction threshold. In this work, the full body neutron dose equivalent has been measured during single-field radiotherapy sessions carried out at different LINAC energies (15, 10 and 6 MV) by using a tissue equivalent (for neutrons) anthropomorphic phantom together with bubble dosemeters. Results have shown that some neutron photoproduction is still present also at lower energies. As a consequence, emitted photoneutrons cannot be ignored and represent a risk contribution for patients undergoing radiotherapy.