Phase II Trial: Low-Dose Radiation + SBRT + Sintilimab + Chemotherapy vs. Sintilimab + Chemotherapy in Locally Advanced or Metastatic Squamous Cell Lung Cancer

Inclusion Criteria: 1. Age ≥ 18 years old and ≤ 75 years old; 2. Histologically or cytologically confirmed squamous cell lung cancer, imaging confirmed locally advanced or metastatic disease (unresectable or not eligible for definitive chemoradiotherapy, stage IIIB-IV); 3. According to the Response Evaluation Criteria in Solid Tumors (RECIST v1.1), there is at least one imaging measurable lesion; 4. Enough to provide quality control qualified tumor tissue or cell wax blocks to detect PD-L1 expression; 5. Have not received any systemic anti-tumor treatment for locally advanced or metastatic disease in the past; Exclusion Criteria: 1. The pathology is small cell lung cancer (SCLC), including lung cancer mixed with SCLC and non-small cell lung cancer (NSCLC)； 2. The pathology is lung adenocarcinoma, including lung cancer mixed with lung adenocarcinoma and lung squamous cell carcinoma; 3. EGFR gene sensitive mutation or ALK fusion positive or ROS1 fusion positive; 4. Previously received the following therapies: anti-PD-1, anti-PD-L1 or anti-PD-L2 drugs or another drug that stimulates or synergistically inhibits T cell receptors; 5. Pregnant or lactating women;