The eligibility criteria are patients with locoregionally recurrent head and neck cancer; good performance status; inoperable, clinical measurable tumor size; good organ function and good compliance. No systemic treatment is in use. Once entering this study, patients will receive angiographies to evaluate bloody supply of the tumor and PET scan with 18F-fluoro-L-BPA as the tracer. Tumor-to- normal tissue ratios were evaluated from static emission scans. Boron concentration of normal tissues is derived from measurement of BPA concentration in the blood. Treatment planning with THORplan will be done after Computerized Tomography (CT) simulation. After treatment plan approved and on the day of treatment, intravenous or intra-arterial L-BPA- Fructose complex 500 mg/kg was administered at a constant rate over about 3 hours before and during neutron irradiation. Neutron beam irradiations were given at the THOR with prescription dose of 20 to 25 Gy (Eq) for the tumor in one fraction on day 1 and repeated on day 30. Patients will be regularly followed up at OPD for toxicities (NCI Common Terminology Criteria) and response evaluation (RECIST criteria)by MRI and PET, time to progression measurement, survival status and change of quality of life. Maximally 27 patients will be enrolled. After first 10 patients, the preliminary results will be reviewed before further patients' enrollment.