This study is for people with advanced cancer of the digestive tract and cancer that cannot be completely removed by surgery. Radiation therapy is commonly used in the treatment of these types of cancer in combination with a chemotherapy drug, called 5-fluorouracil (5-FU). In this study, doctors will administer the standard dose of radiation therapy in combination with an investigational chemotherapy drug, called irinotecan. Irinotecan can decrease the size of tumors and also appears to increase the effectiveness of radiation. The purpose of this study is to determine the highest dose of irinotecan that can be given safely in combination with radiation therapy, and to determine the side effects when these two treatments are given together. Irinotecan is approved by the Food and Drug Administration (FDA) for the treatment of colon cancer, but is not approved for cancers of the digestive tract. However, the FDA is allowing its use in this research study.

Inclusion Criteria:

• Histologically confirmed neoplasm of the upper gastrointestinal tract (pancreas, stomach, duodenum, common bile duct, ampulla of Vater) or metastatic tumor to the upper abdomen.
• Eligible patients include patients with locally advanced unresectable tumors, positive surgical margins, local recurrence and resected stage II-III pancreatic, gastric, duodenum, bile duct or ampulla of Vater carcinoma.
• Performance status SWOG 0-2
• Fully recovered from prior surgery or chemotherapy (greater than or equal to 4 weeks). Patients previously treated with 5-FU or gemcitabine may start therapy 2 weeks after the last dose of 5-FU or gemcitabine.
• Absolute granulocyte count (AGC) > 1500; platelets > 100,000; serum creatinine < 2.0 mg/dl; total bilirubin < 2.0 mg/dl; AST or ALT and alkaline phosphatase < 3 times the upper limit of normal.
• Prior chemotherapy is allowed.

Exclusion Criteria:

• Prior radiation therapy to the upper abdomen
• Tumors of the gastroesophageal junction.
• Other medical, psychological or social circumstances that, in the opinion of the investigator, would prevent participation in the clinical trial
• Pregnancy.