The purpose of the study is to investigate efficacy and safety boron neutron capture therapy (BNCT) administered in combination with cetuximab in the treatment of head and neck cancer that has recurred locally following conventional cancer treatment (surgery and radiation therapy). Boron neutron capture therapy is a special form of radiation therapy, which is based on interaction between boron atoms taken up by the cancerous tissue and neutron irradiation. The boron atoms, located within cancer cells, may capture low-energy neutrons obtained from a nuclear accelerator, which results in splitting up (fission) of the boron atoms, and a high radiation effect within the tumor. Cetuximab is an antibody directed against certain proteins found on cancer cell surface (epidermal growth factor receptors). When administered immediately after BNCT, cetuximab may or may not improve treatment efficacy.