Abstract
PURPOSE: The regional-control of prophylactic irradiation dose reduction of level Va in NPC has not been reported in detailed. We separately evaluated the metastatic nodes of the two sides of each patient’s neck and aim to assess the regional-control based on the irradiation dose reduction of level Va. METHODS AND MATERIALS: We evaluated the regional-control data of 51 NPC patients with 102 neck sides (NS) in our institution from 2020 to 2025. All patients received intensity-modulated radiation therapy (IMRT) ± chemotherapy. The clinical target volume (CTV2) was defined as intermediate risk nodal regions including the ipsilateral level II and III in the NS without nodal spread or with isolated metastases in level VII. CTV3 was defined as low-risk nodal region only including the unilateral or bilateral level Va, and each NS of CTV3 was individually delineated. All patients received IMRT in 30–33 fractions. The Kaplan-Meier method was used to calculate the survival rate, including overall survival (OS), progression-free survival (PFS), local recurrence-free survival (LRFS), and distant metastasis-free survival (DMFS). The equivalent dose in 2 Gy per fraction (EQD2) was calculated according to the formula: EQD2 = d*n((α/β + d)/(α/β + 2d)). RESULTS: The number of patients with N0, N1, and N3 stage is 8 (15.7%), 40 (78.4%), and 3 (5.9%), respectively, the 5- year OS, PFS, LRFS, and DMFS were 87.8%, 79.8%, 97.8%, and 85.5%, respectively. There are 63 CTV3 received prophylactic irradiation dose reduction in level Va (12 patients in the bilateral NS, 39 patients in the unilateral NS). There are 5 PTV3 received prophylactic irradiation dose of 25–34 Gy (EQD2), 7 PTV3 received 48 Gy (EQD2), and 51 PTV3 received 50–51.04 Gy (EQD2), and no patient presented local failure in CTV3. CONCLUSIONS: The prophylactic irradiation dose of level Va can be reduced or even omitted in NPC patients with N0 stage, N1 and N3 stage with or without isolated metastases in the unilateral/bilateral level VII.