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

This study is testing whether a specialized PET scan using a radioactive tracer called 68Ga-PSMA (normally used for prostate cancer imaging) can detect upper gastrointestinal cancers and help determine which patients might benefit from targeted radiation therapy (called endoradiotherapy). These cancers include esophageal, stomach, bile duct, and pancreatic adenocarcinomas. **You may be eligible if...** - You are 18 years old or older - You have active adenocarcinoma of the esophagus, stomach, bile ducts, or pancreas confirmed by CT scan within the last 8 weeks - You are able to give informed consent - The PSMA PET scan can be performed within 2 months of your qualifying CT scan **You may NOT be eligible if...** - You have another active cancer (other than non-melanoma skin cancer) - Your performance status is too low (ECOG score greater than 3) - You are pregnant Talk to your doctor to see if this trial is right for you.