Long-Term Results of Omitting Elective Level IB Irradiation in Node-Negative and Node-Positive Nasopharyngeal Carcinoma

Abstract

Although prior studies have shown that level IB involvement in nasopharyngeal carcinoma (NPC) is rare, many protocols still recommend elective nodal irradiation (ENI) of IB, which can lead to increased toxicities such as mucositis, xerostomia, laryngeal edema, and osteoradionecrosis. The purpose of this study was to evaluate our policy of withholding bilateral elective IB coverage, unless clinically indicated, in patients with node-negative and node-positive NPC. Between 1999 and 2014, 74 patients with NPC were treated with definitive RT. The nodal clinical target volume (CTV) included the bilateral retropharyngeal and level II-V nodes. Contralateral and ipsilateral level IB was omitted on node-negative and node-positive patients to decrease radiation dose to the submandibular glands, oral cavity, mandible, suprahyoid muscles, and larynx, unless there was involvement of IB and/or involvement of structures that drain to IB as the first echelon site. Clinical and treatment characteristics were: median age at diagnosis 51 years (range 14-78), male 76%, White 58%, Asian 24%, Stage III 30%, Stage IVA 49%, Stage IVB 10%. The T and N staging distributions were: T1 14%, T2 15%, T3 18%, T4 54%, N0 24%, N1 19%, N2 47%, N3 9%. The median delivered dose to the GTV was 70 Gy (range 69.96 – 76), to the CTV and upper neck nodes 60 Gy (range 44 – 66) and to lower neck nodes 54 Gy (range 44 – 69.96). Eight-two percent were treated with protons and 96% received chemotherapy including 24% induction and concurrent, 30% concurrent alone, and 38% concurrent and adjuvant. The primary endpoint, locoregional control, and secondary endpoints, including overall survival and disease free survival were estimated by the Kaplan-Meier method. With a median follow-up time of 5.6 years, there were 3 patients with local recurrence alone and 1 patient with synchronous local and regional recurrence. All local recurrences occurred in the high-dose 70 Gy target volume. The one nodal failure was in a patient with persistent disease at the ipsilateral level II and retropharyngeal nodes previously treated to 70 Gy. There was no failure in IB in the entire cohort. The rates of 2- and 5-year local control were 97.2% and 95.7% respectively, of regional control were 98.6% and 98.6% respectively and of overall survival were 91.8% and 83.8% respectively. Thirty-nine percent of patients had g-tube placement before or during radiation therapy. The median weight loss during treatment was 7.6 kg (range 0.2 – 16.1) and 5.4% had more than 15% weight loss. At 2 years, 2.7% of patients had grade 2 xerostomia and 2.7% of patients had osteoradionecrosis of the mandible. There was no grade 3 or higher xerostomia or osteoradionecrosis. ENI to ipsilateral and contralateral level IB for patients with NPC is unnecessary when there is no involvement of 1B or of areas draining to 1B.