This is a Phase II, multicenter, randomized controlled trial to assess the efficacy of Stereotactic Body Radiotherapy (SBRT) in combination with maintenance therapy in patients with advanced pancreatic cancer. The aim is to compare the efficacy of SBRT combined with maintenance therapy versus maintenance therapy alone. The primary outcome is the overall survival (OS) of patients, with secondary endpoints including progression-free survival (PFS), response rates, and quality of life assessments. The study will involve patients with unresectable pancreatic adenocarcinoma who are receiving chemotherapy and have stable disease. The hypothesis is that SBRT, by improving local control, can enhance the benefit of ongoing maintenance therapy and lead to better overall survival outcomes in this patient group.