The goal of this clinical trial is to evaluate the safety of applying BNCT with the dose optimization in patients with recurrent head and neck cancer. The main questions it aims to answer are:

- Dose optimized BNCT are conducted safety in these patients. Participants will receive dose optimized BNCT regulated as 12, 15, 18 Gy-Eq of the mucosal dose.

Inclusion Criteria:

• Signed written informed consent to participate in the clinical trial on their own free will.

• Aged over 20 years at the time of consent obtaining.

• ECOG performance status (PS) of 0-2.

• Histologically confirmed a primary lesion of Head and Neck cancer.

• Following condition:

  1. Locally Recurrent Head and Neck Squamous Cell Carcinoma after chemo radiotherapy or radiation therapy.
  2. Primary Head or Neck Squamous Cell Carcinoma with no indicated of radical radiation therapy for the target lesions.

• More than one the target lesions based on RECIST (version 1.1)

• Local recurrent lesion localized to unilateral.

• Received a fractionated radiation therapy with total doses of ≥40 and ≤80 Gy at around 2 Gy per daily fraction at target lesion sites or an equivalent biologically effective dose.

• ≥50 days have passed since the last irradiation date of the prior radiation therapy at target lesion sites to the day of scheduled BNCT

• Have an estimated survival of ≥90 days after BNCT.

• Estimated able to receive the minimum tumor dose at least 20Gy-Eq.

• Screening test values that meet the following criteria.

• No abnormal findings of clinical concern in chest X-ray exam.

Exclusion Criteria:

• Active multiple primary cancers.
• Distant metastatic lesions.
• Active infections requiring systemic treatment.
• Serious complications.
• Poorly controlled diabetes mellitus.
• Poorly controlled hypertension.
• Chronic lung diseases.
• Kidney diseases.
• Cardiac diseases.
• Other serious complications.
• Phenylketonuria.
• Hereditary fructose intolerance.
• Current or past medical history of serious hypersensitivity to drugs or contrast media.
• Myocardial infarction, unstable angina, or poorly controlled arrhythmia within 6 months prior to the scheduled BNCT.
• Grade ≥3 (CTCAE v4.0) symptom at the target site.
• Tumor invasion of the carotid artery or adjacent to over half of the carotid artery.
• Dental caries whose treatment has not been completed.
• Received antitumor drugs within 4 weeks prior to the scheduled BNCT.
• Participating in a clinical study of an unapproved drug except 18F-F BPA-PET/CT examinations within 4 weeks prior to the scheduled BNCT.
• Implanted with a cardiac pacemaker, ventricular assist device, or the like.
• Inability to immobilize at a right position during irradiation by the investigator (subinvestigator)
• Pregnant or who are breastfeeding during the period of the clinical trial.
• Mental illness or mental conditions.
• Poorly controlled epilepsy.
• Unable to comply with the protocol and to attend follow-up visits.
• With a history of BNCT.
• Considered unfit to participate in this clinical trial as assessed by the investigator.