High-energy linear accelerators for radiotherapy produce fast secondary neutrons due to (γ,n) reaction. Considering the moderating effect of human body, an unavoidable and undesired thermal neutron flux is localized in the tumor area. This study proposes the possibility to employ this neutron background to enhance the radiotherapy efficacy: the thermal neutron peak could be exploited for BNCT applications, delivering an additional therapeutic dose to the photon dose concentrated in tumor cells, acting as a localized radiosensitizer.