Long-Term Outcome in Cervical Lymph Node-Positive Nasopharyngeal Carcinoma Following Intensity Modulated Radiation Therapy With One-Step Cervical Nodal Clinical Target Volume Delineation by Geometric-Anatomic Expansion From Nodal Gross Target Volume: A Double-Center Experience.

PURPOSE

To report long-term results of patients with cervical node-positive (CLN+) nasopharyngeal carcinoma (NPC) treated with intensity modulated radiation therapy with one-step nodal clinical target volume (CTVn) delineation by geometric-anatomic expansion from the nodal gross target volume (GTVn).

METHODS AND MATERIALS

Patients with CLN+ NPC treated with the same one-step-CTVn delineation in two Chinese academic centers were pooled for this study. GTVn was prescribed to 70 Gy equivalent, CTVn1 was omitted, CTVn2 was prescribed to 45 to 55 Gy equivalent, and defined as GTVn + 3 mm geometric expansion (5 mm if radiological extranodal extension-positive [rENE+]) + elective nodal regions defined by anatomic boundary of cervical nodal levels. Regional control (RC) and overall survival (OS) were analyzed. Fifteen randomly selected cases were recontoured for CTVn according to the 2018 International Guidelines (2018-IG). Dose/volume was compared between the two clinical target volume delineation methods.

RESULTS

A total of 807 patients were included (center 1, n = 459; center 2, n = 348). Five-year RC and OS were 95.8% and 86.2%, respectively. Thirty-four patients developed regional failure, and 13/34 (38%) were outside CTVn2: level VIII (parotid node) (9/13), Ib (4/13), and IV (2/13). Seven out of these 9 level VIII failures had pre-existing "equivocal" nodes. All 4 level 1b failures had "equivocal" nodes with very advanced rENE or large (>5 cm) nodal mass in level II. Compared with the 2018-IG, our strategy resulted in significant reduction in nodal volumes received therapeutic (V70) (mean, 100.7 vs. 27.5 cc; P < .001) and prophylactic (V45) (mean, 343.5 vs. 261.2 cc; P < .001) doses and further dose reduction in surrounding organs at risks.

CONCLUSIONS

Our one-step-CTVn delineation by geometric-anatomic expansion from GTVn appears to be a safe and efficient approach in CLN+ NPC, with excellent RC and potential dosimetric benefits in selected patients. Caution is needed for parotid sparing in patients with pre-existing "equivocal" nodes or level Ib sparing in cases with advanced rENE or large (>5 cm) nodal mass in level II.