Postoperative Radiation Therapy for Submandibular Gland Carcinomas: What Is the Optimal Elective Nodal Irradiation Volume?

Abstract

To determine the optimal elective nodal irradiation (ENI) volume in patients with submandibular gland carcinoma (SMGC) treated with postoperative radiation therapy (PORT). A retrospective analysis was performed to investigate 53 patients with SMGC treated with surgery and PORT between 2000 and 2013. Pathological neck nodal metastasis was recorded in 19 patients (39%): 4 with pN1 and 15 with pN2b. The regions of ENI were categorized into bilateral each 3 echelons according to anatomically lymphatic drainages: the 1st echelon for Level I-II and tumor bed, the 2nd echelon for Level III, and the 3rd echelon for Level IV-V. The median radiation dose is 66 Gy. Fifteen patients (28%) received ENI to at least bilateral one echelons adjacent to pathologically involved neck levels. Ten patients (19%) received ENI to at least bilateral 2 echelons (i.e., ipsilateral whole neck and contralateral Level I-III), and 7 patients (13%) received ENI to bilateral 3 echelons (i.e., bilateral whole neck). With a median follow-up of 5.0 years, 9 patients developed nodal failures and one with coincident local recurrence. The 5-year locoregional control (LRC), disease-free survival (DFS), and overall survival (OS) were 78.2%, 62.9%, and 58.5%, respectively. Bilateral ENI to at least one adjacent echelons significantly improved LRC for patients with pT3-4 (P = 0.045), pN(+) (P = 0.001), lymphatic invasion (LI) (P = 0.023), and muscle invasion (MI) (P = 0.044) and improved DFS for patients with pN(+) (P = 0.031). For patients with 2 coincident adverse pathological factors including pT3-4, pN(+), LI, MI, nodal extracapsular spreading, pN2b, and level IV-V nodal involvement, bilateral ENI to at least 2 echelons significantly increased LRC (P = 0.025). For patients possessing ≥ 3 coincident aforementioned adverse pathological factors, ENI to bilateral 3 echelons significantly improved the LRC (P = 0.026). In addition, for patients without aforementioned adverse factors, no nodal recurrence was observed even without bilateral ENI (N = 18). Bilateral ENI to adjacent 1, 2, and 3 echelons are warranted for SMGC patients with 1, 2, and ≥ 3 adverse pathological factors, respectively.