Benzydamine Oromucosal Solution in Oral Mucositis (BOOM)

Inclusion Criteria: * Male and female patients of any ethnic origin ≥18 years of age. * Patients diagnosed with stage III or IV Head and Neck cancer (histologic or cytologic diagnosis), according to VIII AJCC staging system, who are candidate and are about to start RT, with or without concomitant CT, with curative intent, either with exclusive or postoperative intent. * Eastern Cooperative Oncology Group (ECOG) performance status with a score of 0, or 1, or 2. * Patients legally capable of giving their consent to participate in the study and available to sign and date the written informed consent and the Declaration of consent for the processing of personal data. * Women of childbearing potential or with no menses for a period \< 12 months must have a negative pregnancy test at Visit 0 and have to agree not to start a pregnancy from the signature of the informed consent up to the end of the study, using an appropriate birth control method, such as combined oestrogen-progestin containing hormonal contraceptives (e.g., oral, injectable, transdermal), progestin-only hormonal contraceptives (e.g., oral, injectable, implantable), intrauterine device (IUD) or Intrauterine hormone-releasing System (IUS) in combination with male condom, bilateral tubal occlusion, vasectomised partner, sexual abstinence. The following definitions will be considered: * Woman of childbearing potential (WOCBP): i.e., fertile, following menarche and until becoming post-menopausal, unless permanently sterile. Permanent sterilization methods include hysterectomy, bilateral salpingectomy and bilateral oophorectomy. Exclusion Criteria: * Patients with reported allergy to benzydamine or another component of the formulation used. * Any contraindications listed in the local product's Summary of Product Characteristics (SmPCs). * Patients with prior head and neck RT (in the previous 6 months), or patient who received a palliative treatment. * Patients with distant metastatic disease and/or severe cognitive impairment and/or clinically symptomatic brain metastases and/or patients with significant comorbid conditions. * Patients with mucositis due to other medical conditions (e.g., gastro-oesophageal reflux, autoimmune disease, etc.). * Patients who use other oromucosal products (over the counter or prescription) for the same disease. * Prescription of other rinses (anaesthetics like "magic mouthwashes" or others), except from sodium bicarbonate rinses. * Use of chlorhexidine, other anti-inflammatory mouthwashes solutions, misoprostol, granulocyte macrophage colony-stimulating factor (GM-CSF) and sucralfate gel. * Employment of antifungal or antibiotic drugs as prophylaxis for mucositis; any therapeutic use in case of overt clinical infections is allowed. * Patients treated with other therapies that can cause mucositis, except for the therapies for their primary condition. * Patients treated with any topical anti-inflammatory/analgesic products for the mucositis. * Any other product that can interfere with the evaluation of pain or inflammatory state, according to the Investigator's assessment.