To evaluate the patterns of nodal failure and toxicity in clinically negative necks of N0-1 nasopharyngeal carcinoma (NPC) patients who were treated with intensity modulated radiation therapy (IMRT) but did not receive elective neck irradiation (ENI) to level IV and Vb nodes.

We conducted a phase 2 prospective study in N0-1 NPC patients treated with IMRT. ENI included the retropharyngeal nodes and levels II to Va but omitted levels IV and Vb in clinically negative necks. Patterns of nodal failure, regional control (RC), and late toxicity were evaluated.

Between 2001 and 2008, a total of 212 patients (128 N0 and 84 N1) were enrolled in the study. Seven patients (4 in-field and 3 out-of-field) developed nodal failure. One patient (0.5%) developed nodal failure at level Vb, but no patients developed nodal failure at level IV. The 5-year RC rates of the entire group, N0 patients and N1 patients were 95.6%, 98.2%, and 91.3%, respectively. Fifteen patients (7.1%) developed distant metastases. The 5-year distant failure-free survival (DFFS) and overall survival (OS) rates were 91.4% and 89.8%, respectively. The rates of grade 2 or greater skin dystrophy, subcutaneous fibrosis and xerostomia were 6.2%, 16.6%, and 17.9%, respectively.

The rate of out-of-field nodal failure when omitting ENI to levels IV and Vb in clinically negative necks of patients with N0-1 NPC was extremely low; therefore, a further phase 3 study is warranted.