PULSAR Combined With Immunotherapy for Unresectable Locally Advanced Gastric Cancer

Inclusion Criteria: Age 19 or more years. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-2. Histologically confirmed gastric adenocarcinoma. Tumor biomarker status: HER-2 negative, EBV negative, and Microsatellite Stable (MSS). Unresectable, locally advanced extent at initial staging (Para-aortic lymph node \[PALN\] and Supraclavicular lymph node \[SCN\] metastases are allowed). Has completed 3 or more cycles of first-line systemic therapy combined with immunotherapy without evidence of disease progression. Presence of at least one evaluable lesion according to RECIST v1.1 that is deemed safely irradiable by the investigator. Voluntary written informed consent provided by the subject. Exclusion Criteria: Pregnant or lactating women. Presence of brain metastases or leptomeningeal involvement. Prior history of radiation therapy to the intended target site. Severe uncontrolled comorbidities that, in the investigator's opinion, limit study participation or treatment compliance (e.g., uncontrolled infection, heart failure, arrhythmia, psychiatric illness). Inability or unwillingness to comply with the study protocol procedures. Any condition deemed inappropriate for study participation by the principal investigator or attending physician.