Long-term Outcomes Following Individualized Elective Primary Tumor CTV Delineation Based on Stepwise Spread Patterns of Nasopharyngeal Carcinoma Treated with Intensity-modulated Radiotherapy.

Abstract

Purpose: Our institution has developed an individualized elective primary tumor clinical target volume (CTVp) delineation protocol for nasopharyngeal carcinoma (NPC) based on stepwise tumor spread patterns in intensity-modulated radiotherapy (IMRT) for over ten years. Herein, we report the long-term efficacy and toxicities in NPC patients treated under this protocol.

Methods and materials: A total of 7,262 histologically proven, nonmetastatic NPC patients treated with IMRT following this individualized delineation protocol were retrospectively evaluated. The 5-year rates for local relapse-free survival (LRFS), regional relapse-free survival (RRFS), distant metastasis-free survival (DMFS), progression-free survival (PFS), and overall survival (OS) were estimated. Dose-volume histogram (DVH) parameters for patients with local relapse were compared to those of propensity score-matched (PSM) without local relapse. Dosimetric comparisons of our delineation protocol with the 2018 International Guideline (2018-IG) were conducted on representative early- and advanced-stage NPC cases.

Results: The 5-year LRFS, RRFS, DMFS, PFS and OS were 93.6%, 94.4%, 86.8%, 77.8%, and 86.0%, respectively. 92.3% of local relapses and 86.0% of regional relapses occurred within the 95% isodose lines and were considered GTV in-field failures. No significant differences in DVH parameters were observed between the local relapse group and the propensity score-matched non-relapse group. Compared with the 2018-IG, our contouring protocol resulted in a 58.4% and 48.3% reduction in PTV70, and an 80.8% and 62.8% reduction in PTV60 for early and advanced-stage disease, respectively. Late grade 3 toxicities included ototoxicity (1.8%), xerostomia (0.2%), dysphagia (0.2%), temporal lobe injury (0.2%), and trismus (0.1%).

Conclusion: Individualized elective CTVp delineation based on the stepwise spread patterns of nasopharyngeal carcinoma achieved excellent long-term outcomes and reduced the irradiated volumes at equivalent dose levels compared to the 2018-IG.