68Ga-PSMA PET Imaging of Upper Metastatic Gastric Cancers to Determine Eligibility to Endoradiotherapy

Inclusion Criteria: * Age 18 years and older * Active cancer of the type adenocarcinoma (of the esophagus, of the stomach, of the bile ducts, or of the pancreas) documented by a CT scan performed within the last 8 weeks at the time of recruitment. * An active cancer is defined as at least one lesion identified as stable or progressive neoplastic on CT imaging. * A lesion treated with local therapy (e.g., external radiotherapy, cryoablation, radiofrequency ablation, resection) is not counted for inclusion criteria if this is done between the CT scan and the 68Ga-PSMA PET imaging. A lesion treated prior to the last CT scan may be considered eligible if progression is documented at the last CT scan. * Able to provide free and informed consent. * Feasibility to perform 68Ga-PSMA PET within 2 months of the CT scan that was used for inclusion. Exclusion Criteria: * Other active cancer (non-metastatic non-melanoma skin cancer excluded). Cancer in remission for at least 3 years will not be considered active. * ECOG \> 3. * Pregnant woman. * Unable to follow study rules.