Induction High-Low Dose Radiotherapy Plus Anti-PD-1 Followed by Definitive Radiotherapy in Recurrent Nasopharyngeal Carcinoma (Single-Arm Phase II)

This single-arm, single-center phase II trial evaluates the safety and efficacy of a non-continuous radio-immunotherapy strategy for recurrent nasopharyngeal carcinoma (NPC) unsuitable for surgery. Induction consists of three fractions of low-dose radiotherapy (1.5 Gy ×3) plus high-dose boosts (5 Gy ×3 to tumor core with carotid/mucosal sparing) combined with anti-PD-1 (240 mg IV on Day 1 and Day 22). After a 21-28-day interval, definitive IMRT (2 Gy ×28, 5 days/week) is delivered without concurrent immunotherapy to minimize immune damage. Anti-PD-1 maintenance (240 mg IV Q3W) starts within 2 weeks after radiotherapy for up to 12 months or until progression/toxicity. The primary endpoint is ORR at 3 months post-radiotherapy; secondary endpoints include 3-year OS, 3-year PFS, safety (NCI-CTCAE v5.0), and quality of life (EORTC QLQ-C30). Key eligibility: histologically confirmed non-keratinizing NPC (WHO II/III), rT2-rT4, ECOG 0-1, adequate organ function.