Long-term outcome in cervical lymph node-positive nasopharyngeal carcinoma following IMRT with one-step cervical nodal CTV delineation by geometric-anatomic expansion from nodal GTV: A double-center experience.

Abstract

To report long-term results of cervical node-positive (CLN+) nasopharyngeal carcinoma (NPC) patients treated with IMRT with one-step nodal clinical target volume (CTVn) delineation by geometric-anatomic expansion from the nodal gross target volume (GTVn). 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 45-55 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 2018 International Guidelines (2018-IG). Dose/volume was compared between the two CTV delineation methods. 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 preexisting "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<0.001) and prophylactic (V45) (mean: 343.5 vs 261.2 cc, p<0.001) doses, and further dose reduction in surrounding organs-at-risks. 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 benefit in selected patients. Caution is needed for parotid sparing in patients with preexisting "equivocal" nodes or level Ib sparing in cases with advanced rENE or large (>5 cm) nodal mass in level II.