Gemcitabine and Radiation Therapy in Treating Patients With Cancer of the Pancreas

DISEASE CHARACTERISTICS: Histologically confirmed invasive adenocarcinoma of the pancreas Prior gross total resection via a pancreaticoduodenectomy (Whipple resection or total pancreatectomy) within the past 2 months No clinical evidence of gross residual disease at time of surgery No focally positive margins (tumor at the margin) No unresected nodal disease or metastatic disease to the liver, peritoneal surfaces, or elsewhere PATIENT CHARACTERISTICS: Age: Over 18 Performance status: ECOG 0-2 Life expectancy: More than 6 months Hematopoietic: Granulocyte count greater than 1,500/mm3 Hemoglobin greater than 10 g/dL Platelet count greater than 100,000/mm3 Hepatic: Bilirubin less than 2.0 mg/dL Renal: Creatinine less than 2.0 mg/dL Other: Able to maintain adequate oral nutrition Documented stable weight (no more than 5 lbs weight loss) for at least 2 weeks prior to study No other malignancy within the past 2 years except inactive nonmelanoma skin cancer or carcinoma in situ of the cervix or breast Non-metastatic prostate cancer allowed if more than 2 year survival likely No other serious medical or psychiatric illness that would preclude study or limit survival to less than 2 years Not pregnant Negative pregnancy test Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent routine growth factors Chemotherapy: No prior chemotherapy for pancreatic cancer Endocrine therapy: Not specified Radiotherapy: No prior abdominal radiotherapy for pancreatic cancer Surgery: See Disease Characteristics