Study of Stereotactic Body Radiation Therapy in Patients With Intact Pancreatic Cancer

Inclusion Criteria: * Patients must have histologically confirmed, unresected cancer of the pancreas or ampulla. The cancer may include any invasive histology (e.g. adenocarcinoma, neuroendocrine carcinoma). * Patients must have measurable radiographic disease.Patients with previous complete resection are only eligible if there is measurable radiographic disease which is clearly felt to represent locally recurrent disease. * Patients may receive any number of cycles of chemotherapy prior to treatment with SBRT, but not within 2 weeks of the first fraction of RT. * Age \> or = 18 years. * Eastern Cooperative Oncology Group (ECOG) performance status \< or = 2 (Karnofsky \> or = 60%) * Life expectancy of greater than 3 months. * Patients must have normal organ and marrow function. * Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: * Concurrent investigational therapy delivered over the period of treatment or observation (28 days post-RT) for dose limiting toxicity. * Prior radiation therapy to the abdominal area which would overlap with the proposed area of treatment. * Pregnancy. * Primary disease \> 7.5 cm in largest diameter as measured by CT or MRI. * Gross extension of tumor into the lumen of the duodenum. * Uncontrolled intercurrent illness including, but not limited to ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. * Use of bevacizumab or vascular endothelial growth factor inhibitor chemotherapy within 3 months before RT or 6 months after RT.