Introduction:Patients with nasopharyngeal carcinoma(NPC) sporadically develop abnormal adenoids.Nasopharyngeal adenoids are usually included in the gross tumor volume(GTV) but may have different therapeutic responses than tumor tissue.Therefore,distinguishing adenoids from tumor tissue may be required for precise and efficient chemoradiotherapy and radiotherapy.We characterized nasopharyngeal adenoids and investigated the therapeutic responses of NPC and nasopharyngeal adenoids using magnetic resonance imaging(MRI).Methods:MRI data from 40 NPC patients with a coexisting adenoid mass before and after treatment were analyzed.The features of the adenoid masses,including location,striped appearance,size,interface,symmetry/asymmetry,and cysts,were evaluated.Treatment response were scored according to the World Health Organization guidelines.Results:A striped appearance was observed in 36 cases before treatment and in all cases after treatment.In these 36 cases,the average GTVs including and excluding the uninvolved adenoids were 19.8 cm~3 and 14.8 cm~3,respectively.The average percentage change after excluding the uninvolved adenoids from the GTV was 31.0%.Stable disease in the adenoids was identified in 27(96.4%) of 28 patients after neoadjuvant chemotherapy,while NPC clearly regressed.Partial adenoid responses were identified in 33(82.5%) of 40 patients at 3 months after chemoradiotherapy or radiotherapy,whereas complete tumor responses were achieved in all patients.Six months after treatment,the adenoids continued to atrophy but did not disappear,and tumor recurrence was not found.Conclusions:Nasopharyngeal adenoids and carcinoma tissue in NPC patients can be distinguished by using MRI and have different responses to chemoradiotherapy and radiotherapy.These findings contribute to better delineating the GTV of NPC,based on which spatially optimized strategies can be developed to render precise and efficient chemoradiotherapy and radiotherapy.Additionally,we observed a clear difference in the responses of these two tissue types to current therapies.This finding may reduce or avoid unnecessary biopsies or overtreatment. Introduction: Patients with nasopharyngeal carcinoma (NPC) sporadically develop abnormal adenoids. Nasopharyngeal adenoids are usually included in the gross tumor volume (GTV) but may have different therapeutic responses than tumor tissue. Before, distinguishing adenoids from tumor tissue may be required for precise and efficient chemoradiotherapy and radiotherapy. We describe nasopharyngeal adenoids and investigated the therapeutic responses of NPC and nasopharyngeal adenoids using magnetic resonance imaging (MRI). Methods: MRI data from 40 NPC patients with a coexisting adenoid mass before and after treatment were analyzed. The features of the adenoid masses, including location, striped appearance, size, interface, symmetry / asymmetry, and cysts, were evaluated. Treatment response were scored according to the World Health Organization guidelines. Results: A striped appearance was observed in 36 cases before treatment and in all cases after treatment.In these 36 cases, the average GTVs including and excluding the uninvolved adenoids were from 19.8 cm 3 and 14.8 cm 3, respectively. The average percentage change after excluding the uninvolved adenoids from the GTV was 31.0%. Stable disease in the adenoids was identified in 27 (96.4%) of 28 patients after neoadjuvant chemotherapy, while NPC clearly regressed. Partially adenoid responses were identified in 33 (82.5%) of 40 patients at 3 months after chemoradiotherapy or radiotherapy, example complete tumor responses were achieved in all patients. Six months after treatment, the adenoids continued to atrophy but did not disappear, and tumor recurrence was not found. Conclusions: Nasopharyngeal adenoids and carcinoma tissue in NPC patients can be distinguished by using MRI and have different responses to chemoradiotherapy and radiotherapy. These findings contribute to better delineating the GTV of NPC, based on which spatially optimized strategies can be developed to render precise and efficient chemoradiotherapy and radiotherapy. Additionally, we observed aclear difference in the responses of these two tissue types to current therapies. This finding may reduce or avoid unnecessary biopsies or overtreatment.