Long-term Outcomes Following Individualized Primary Tumor Clinical Target Volume Delineation Based on Stepwise Spread Patterns of Nasopharyngeal Carcinoma Treated With Intensity-Modulated Radiotherapy.

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 radiation therapy for over 10 years. Herein, we report the long-term efficacy and toxicities in patients with NPC treated under this protocol.

Methods And Materials: A total of 7262 patients with histologically proven nonmetastatic NPC treated with intensity modulated radiation therapy following this individualized delineation protocol were retrospectively evaluated. Survival rates were estimated using the Kaplan-Meier method. Dose-volume histogram parameters for patients with local relapse were compared with those of propensity score-matched 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 local relapse-free survival, regional relapse-free survival, distant metastasis-free survival, progression-free survival, and overall survival 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 in-field failures. No significant differences in dose-volume histogram parameters were observed between the local relapse group and the propensity score-matched nonrelapse 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 diseases, respectively. Late grade 3 toxicities included ototoxicity (1.8%), xerostomia (0.2%), dysphagia (0.2%), temporal lobe injury (0.2%), and trismus (0.1%).

Conclusions: 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 with the 2018-IG.