Patients with stage III non-small-cell lung cancer (NSCLC) who receive neoadjuvant chemoimmunotherapy may achieve good response in the primary tumor but still have residual nodal disease after surgery (ypTanyN⁺M0), which is associated with poor prognosis in retrospective analyses from our center. In prior trials such as LungART and PORT-C, postoperative radiotherapy (PORT) did not improve disease-free survival in completely resected stage IIIA-N2 NSCLC after adjuvant chemotherapy, suggesting that PORT should not be used indiscriminately. However, recent preclinical and translational data indicate that radiotherapy can enhance antitumor immunity, remodel the tumor microenvironment, and synergize with immune checkpoint inhibitors via immunogenic cell death, improved T-cell trafficking, and tertiary lymphoid structure formation.

This single-center randomized phase II study will evaluate whether adding postoperative involved-field nodal radiotherapy to standard PD-1 maintenance therapy can improve disease-free survival compared with PD-1 maintenance alone in patients with ypTanyN⁺M0 NSCLC after neoadjuvant chemoimmunotherapy and R0 resection.

Inclusion Criteria:

• Age 18-75 years, male or female.
• Histologically confirmed NSCLC (adenocarcinoma, squamous cell carcinoma, or other NSCLC subtypes).
• Clinical stage IIIA/IIIB at initial diagnosis, deemed suitable for neoadjuvant chemoimmunotherapy followed by surgery according to MDT.
• Completed 2-4 cycles of platinum-based doublet chemotherapy plus PD-1 inhibitor as neoadjuvant therapy.
• Underwent R0 resection (anatomical lobectomy or pneumonectomy with mediastinal lymph node dissection).
• Postoperative pathological stage ypT_anyN⁺M0 (residual nodal metastasis in mediastinal or hilar lymph nodes).
• ECOG performance status 0-1.
• Adequate hematologic, hepatic, and renal function per protocol-defined lab thresholds.
• Able to start postoperative radiotherapy and/or PD-1 maintenance within 4-10 weeks after surgery (or after recovery from postoperative complications, as clinically appropriate).
• Signed written informed consent.

Exclusion Criteria:

• Positive surgical margins (R1 or R2) or incomplete resection.
• Prior thoracic radiotherapy that would overlap with planned treatment fields.
• Active, uncontrolled infection or unresolved ≥ Grade 2 immune-related adverse events.
• History of severe autoimmune disease requiring systemic immunosuppression.
• Uncontrolled interstitial lung disease or significant pulmonary fibrosis.
• Symptomatic or untreated central nervous system metastases at enrollment.
• Any condition that, in the investigator's judgment, would compromise patient safety or protocol compliance.