Long-Term Outcome Following Intensity-Modulated Radiotherapy Delivered Using Individualized Clinical Target Volume Delineation Based on Stepwise Spread Pattern of Nasopharyngeal Carcinoma

Abstract

<h3>Purpose/Objective(s)</h3> The optimal method for clinical target volume delineation in nasopharyngeal carcinoma has not yet been determined. We have developed an individualized CTV delineation protocol based on the stepwise spread patterns of NPC. This study aimed to determine the long-term outcomes and toxicities in NPC patients receiving intensity-modulated radiotherapy with individualized CTV delineation. <h3>Materials/Methods</h3> We retrospectively reviewed the data of patients with newly diagnosed nondisseminated NPC who underwent IMRT using our individualized CTV delineation protocol. A total of 7,262 patients with NPC (79.3% patients in stage III-IVA) treated between April 2009 and December 2015 were included in this study. Dose–volume statistics, clinical outcomes, patterns of failures and toxicities were assessed. To analyze dose distribution of patients with or without local recurrence, propensity score matching (PSM) was performed to compare the dose between the two groups matched by age, sex, histological type, T category, N category, chemotherapy and gross tumor volume of primary tumor and enlarged retropharyngeal lymph nodes (GTVnx) in a 1:1 ratio. <h3>Results</h3> Median follow-up was 67.3 (range, 2.0-118.7) months. The 5-year local relapse–free survival, regional relapse–free survival, distant metastasis–free survival, progression–free survival, and overall survival rates were 93.6%, 94.4%, 86.8%, 77.8%, and 86.0%, respectively. In-field failure is the major locoregional failure pattern, accounting for 92.3% patients of local and 86% of regional recurrence. Age and T classification were independent prognostic for LRFS, DMFS, PFS, and OS in multivariate analysis. Late grade 3 toxicities were mild and included ear injury (1.8%), xerostomia (0.2%), dysphagia (0.2%), brain injury (0.2%), and trismus (0.1%). No grade 4 toxicity occurred during IMRT or follow-up. PSM analysis revealed no significant difference between minimum (P = 0.815), maximum (P = 0.595), and mean (P = 0.700) dose to the planning tumor volume of primary tumor and enlarged retropharyngeal lymph nodes (PTVnx) between patients with local recurrence and the matched patients without local recurrence. <h3>Conclusion</h3> Our stepwise CTV delineation protocol appears to be a promising strategy for improving outcomes in NPC.