Effects of omitting elective neck irradiation to nodal Level IB in nasopharyngeal carcinoma patients with negative Level IB lymph nodes treated by intensity-modulated radiotherapy: a Phase 2 study

Abstract

Objective: To investigate the need for elective neck irradiation (ENI) to nodal Level IB in patients with nasopharyngeal carcinoma (NPC) with negative Level IB lymph nodes (IB-negative) treated by intensity-modulated radiotherapy (IMRT). Methods: We conducted a Phase 2 prospective study in 123 newly diagnosed IB-negative patients with NPC treated by IMRT, who met at least 1 of the following criteria: (1) unilateral or bilateral Level II involvement with 1 of the following: Level IIA involvement or any Level II node ≥2 cm/with extracapsular spread; (2) ≥2 unilateral node-positive regions. Bilateral Level IB nodes were not contoured as part of the treatment target and treated electively. Level IB regional recurrence rate; pattern of treatment failure; 3-year overall survival (3y-OS), 3-year local control (3y-LC) and 3-year regional control (3y-RC) rates; toxicities; and dosimetric data for planning target volumes, organs at risk, Level IB and submandibular glands (SMGs) were evaluated. Results: Two patients developed failures at Level IB (1.6%). The 3y-LC, 3y-RC and 3y-OS rates were 93.5%, 93.5% and 78.0%, respectively. Bilateral Level IB received unplanned high-dose irradiation with a mean dose (Dmean) ≥50 Gy in 60% of patients. The average Dmean of bilateral SMGs was approximately 53 Gy. Conclusion: ENI to Level IB may be unnecessary in IB-negative patients with NPC treated by IMRT. A further Phase 3 study is warranted. Advances in knowledge: Based on the results of this first Phase 2 study, we suggest omitting ENI to Level IB in Ib-negative patients with NPC with extensive nodal disease treated by IMRT.