The performance of the predictive models for the occurrence and severity of oropharyngeal mucositis established using either oral cavity contouring method or mucosa surface contouring method was unsatisfactory in nasopharyngeal carcinoma (NPC). Whereas the predictive model of a mucosal contouring method based on swallowing-induced breakthrough pain exhibited better overall performance in locally advanced NPC. Therefore, the investigators aimed to conduct a prospective, multicenter, real-world observational study to further assess the predictive efficacy of this mucosal delineation method for radiation-induced oropharyngeal mucositis in NPC.