Inclusion Criteria:
* Age: 18-75 years, regardless of gender.
* Histologically confirmed pancreatic ductal adenocarcinoma (PDAC).
* Previously untreated, locally advanced unresectable or metastatic PDAC, with at least one measurable lesion (RECIST v1.1) not previously irradiated.
* ECOG Performance Status (PS): 0-1.
* Expected survival ≥ 3 months.
* Willing and able to comply with study procedures, treatment, and follow-up.
* No contraindications to radiotherapy.
* Adequate organ function: WBC ≥ 2.5×10⁹/L, ANC ≥ 1.5×10⁹/L; Platelets ≥ 75×10⁹/L; Hemoglobin (HGB) ≥ 90 g/L (no transfusion or EPO dependence within 7 days); Total bilirubin (Tbil) ≤ 1.5×ULN; ALT/AST ≤ 5×ULN;Albumin ≥ 30 g/L; INR ≤ 1.5×ULN; Serum creatinine (Cr) ≤ 1.5×ULN Urine protein ≤ 1+
* HBsAg-positive patients must have HBV-DNA ≤ 1×10³ IU/mL (copies/mL). If HBV-DNA ≥ 1×10³ IU/mL, patients may still be eligible if chronic HBV is stable and not expected to increase risk, per investigator assessment.
* Voluntary participation with signed informed consent form.
Exclusion Criteria:
* History of severe hypersensitivity to chimeric, human(ized) antibodies, or fusion proteins.
* Pregnant or breastfeeding women, or men/women of childbearing potential unwilling/unable to use effective contraception during the study.
* Other malignancies within 5 years, except: Malignancies treated with curative intent and no known active disease for ≥5 years with low recurrence risk; Adequately treated non-melanoma skin cancer or lentigo maligna without disease evidence; Adequately treated carcinoma in situ (e.g., cervical, breast) with no current disease.
* Symptomatic moderate/severe pleural effusion or ascites.
* Active bleeding or coagulopathy (PT \>16s, APTT \>43s, INR \>1.5×ULN), bleeding tendency, or current use of thrombolytics/anticoagulants/antiplatelets.
* GI bleeding within 6 months or high bleeding risk (e.g., active ulcer with occult blood++). If occult blood+ persists, endoscopy required.
* High-risk esophageal/gastric varices needing intervention.
* History of drug abuse, psychiatric disorder, or inability to abstain.
* Solid organ/bone marrow transplant, or active autoimmune disease requiring systemic treatment within 2 years.
* Immunodeficiency or HIV infection.
* Objective evidence of pulmonary fibrosis, interstitial lung disease, pneumoconiosis, radiation-/drug-induced pneumonitis, or severely impaired pulmonary function.
* Major surgery within 4 weeks or minor surgery within 1 week (e.g., tooth extraction).
* Vaccination within 30 days before the first dose.
* Abdominal fistula, GI perforation, or abscess within 4 weeks.
* Any clinically significant abnormality affecting safety per investigator, including: Active infection requiring systemic therapy; Uncontrolled diabetes/hypertension (BP \>140/90 mmHg despite ≤2 antihypertensives); Myocardial infarction within 6 months; Thyroid dysfunction (\>NCI CTCAE v4.0 Grade 1).
* Other conditions deemed ineligible by the investigator.
