Locoregional Control and Mild Late Toxicity After Reducing Target Volumes and Radiation Doses in Patients With Locoregionally Advanced Nasopharyngeal Carcinoma Treated With Induction Chemotherapy (IC) Followed by Concurrent Chemoradiotherapy: 10-Year Results of a Phase 2 Study.

Purpose: To evaluate the long-term locoregional control, failure patterns, and late toxicity after reducing the target volume and radiation dose in patients with locoregionally advanced nasopharyngeal carcinoma patients treated with induction chemotherapy (IC) plus concurrent chemoradiotherapy (CCRT).

Methods And Materials: Previously untreated patients with locoregionally advanced nasopharyngeal carcinoma were recruited into this prospective study. All patients received 2 cycles of IC followed by CCRT. The gross tumor volumes of the nasopharynx (GTVnx) and the neck lymph nodes (GTVnd) were delineated according to the post-IC tumor extension and received full therapeutic doses (68 Gy and 62-66 Gy, respectively). The primary tumor shrinkage after IC was included in the high-risk clinical target volume (CTV1) with a reduced dose of 60 Gy. The locoregional recurrence-free survival (LRRFS), distant metastasis-free survival (DMFS), and overall survival (OS) were calculated using the Kaplan-Meier method. The location and extent of locoregional recurrences were transferred to pretreatment planning computed tomography for dosimetry analysis.

Results: There were 112 patients enrolled in this study. The average mean dose of post-GTVnx, post-GTVnd (left), post-GTVnd (right), post-CTV1, and post-low-risk clinical target volume (CTV2) was 75.24, 68.97, 69.16, 70.49, and 63.37 Gy, respectively. With a median follow-up of 125.95 months, the 10-year LRRFS, DMFS and OS were 89.0%, 83.3%, and 75.9%, respectively. There were 8 local recurrences and 6 regional recurrences in 12 patients. All 8 of the local recurrences were in-field; among the 6 regional recurrences, 4 were in-field, 1 was marginal, and 1 was out-field. The most common late toxicities were grade 1 to 2 subcutaneous fibrosis, hearing loss, and xerostomia. No grade 4 late toxicities were observed.

Conclusions: Reduction of the target volumes according to the post-IC tumor extension and radiation dose to the post-IC tumor shrinkage could yield excellent long-term locoregional control with limited marginal and out-field recurrences and mild late toxicities.