Efficacy of Stereotactic Body Radiotherapy (SBRT) Combined With Maintenance Therapy Compared to Maintenance Therapy Alone in Advanced Pancreatic Cancer

Inclusion Criteria: * Age 18 to 70 years old. * Histologically or cytologically confirmed diagnosis of pancreatic - adenocarcinoma. * No prior radiation therapy for pancreatic cancer. * At least one measurable lesion of the primary pancreatic tumor as per RECIST 1.1 criteria, eligible for SBRT. * Completion of first-line chemotherapy with stable disease (SD) or partial response (PR) after ≥4 months of treatment. * ECOG performance status of 0-2. * Expected survival of ≥3 months. * Adequate organ function within 14 days prior to enrollment: * Hemoglobin (Hb) ≥ 90 g/L * Absolute neutrophil count (ANC) ≥ 1.5×10⁹/L * Platelets (PLT) ≥ 75×10⁹/L * Total bilirubin ≤ 1.5× ULN or direct bilirubin ≤ ULN * ALT/AST ≤ 2.5× ULN * ALP ≤ 2.5× ULN * Serum creatinine ≤ 1.5× ULN or calculated creatinine clearance ≥ 40 mL/min * Urine protein \< 2+ (if ≥2+ on dipstick, 24-hour urine protein must be \< 2g) * No use of systemic corticosteroids in the last 7 days prior to enrollment (physiological corticosteroid replacement is allowed). * Women of childbearing potential and men must use effective contraception during the study and for 12 months following treatment completion. * Voluntary participation with signed informed consent. * Ability to comply with the study schedule. Exclusion Criteria: * Currently participating in any interventional clinical trial or having received other investigational drugs or devices within 4 weeks prior to enrollment. * Peritoneal metastasis. * Known active central nervous system (CNS) metastasis and/or carcinomatous meningitis. * Receiving systemic corticosteroid treatment within 7 days prior to enrollment (except for physiological doses). * Active, untreated hepatitis B (HBsAg positive and detectable HBV-DNA) or active hepatitis C infection (HCV antibody positive and detectable HCV RNA). * Pregnant or breastfeeding women. * Any severe or uncontrolled systemic disease, including: * QTc interval ≥ 480 ms * Unstable angina * NYHA class III-IV congestive heart failure * Arterial thromboembolism (MI, unstable angina, stroke, TIA) within 6 months prior to enrollment * Uncontrolled hypertension (systolic BP ≥ 150 mmHg, diastolic BP ≥ 90 mmHg) * Active pulmonary tuberculosis, severe infections, or other uncontrolled diseases * Active gastrointestinal perforation, fistula, or bowel obstruction. * Inadequately controlled diabetes (fasting blood glucose \> 10 mmol/L). * History of mental illness preventing compliance with treatment. * Active bleeding or significant coagulation abnormalities within the last 30 days. * Previous gastrointestinal perforation or other serious gastrointestinal conditions in the past 6 months. * Participation in other trials that may interfere with this study.