Inclusion Criteria:  Patients with symptomatic osteoradionecrosis with a PENTOCLO protocol indication (decided in a multi-disciplinary staff). Patient should understand to any protocol-specific procedures performed. Patient who did not object to participate after being informed of the study. Patient should be able and willing to comply with study visits and procedures as per protocol. Patients must be affiliated to a social security system or beneficiary of the same. Patients must be over 18 years old (legal age).  Exclusion Criteria:  Excluded forms of the disease: mandibular osteoradionecrosis complicated by mandibular fracture and / or hyperalgesic (resistant to analgesic treatment of stage III). Contraindications specific to the treatment under study (allergy to one of the PENTOCLO treatments, contraindication to 18FDG PET-CT). Associated pathology that contra-indicate on of the PENTOCLO treatment. Pregnant woman, declaring likely to be pregnant or breastfeeding. Chilbearing age women must declare not being pregnant and use effective contraception. Impossibility to submit to the medical follow-up of the test for geographical, social or psychological reasons. Patient under guardianship or deprived of his liberty by a judicial or administrative decision or unable to express its opposition to participating in the study.