Chemoradiation and Radiosurgery Boost in Treating Patients With Locally Advance Pancreatic Cancer That May or May Not be Removed by Surgery

Inclusion Criteria: * Patients must have histologically or cytologically-confirmed pancreatic adenocarcinoma * For the initial dose escalation study, patients must have locally advanced / unresectable pancreatic cancer; these are defined as follows: * No distant metastases * Hepatic artery encasement * Superior mesenteric artery (SMA) encasement \> 180 degrees * Any celiac axis abutment * Unreconstructable superior mesenteric vein (SMV)/portal occlusion * Aortic invasion or encasement * Metastases to lymph nodes beyond the field of resection * For the expansion phase, patients must have borderline resectable or locally advanced / unresectable pancreatic cancer; these are defined as follows: * No distant metastases * At least 45 degree abutment of the hepatic artery or SMA * Any celiac axis abutment * Near complete occlusion of the SMV or portal vein * Unreconstructable or reconstructible SMV/portal occlusion * Aortic invasion or encasement * Metastases to lymph nodes beyond the field of resection * Patients must have evaluable disease * Women of childbearing potential must be non-pregnant (negative pregnancy test within 72 hours prior to radiation simulation, postmenopausal woman must have been amenorrheic for at least 12 months to be considered of non-childbearing potential) and nonlactating, and men and women must be willing to exercise an effective form of birth control (abstinence/contraception) while on study and for 3 months after therapy completed * Eastern Cooperative Oncology Group (ECOG) performance status determined to be between 0 and 1 * Absolute neutrophil count (ANC) \>= 1,500/ul * Platelets (PLT) \>= 100,000/ul * Subjects must sign a written informed consent and Health Insurance Portability and Accountability Act (HIPAA) consent prior to performance of study-specific procedures or assessments and must be willing to comply with treatment and follow up * Bilirubin less then 1.5 x upper limit of normal (ULN) * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) \< 3 x ULN * Serum creatinine \< 1.5 x ULN Exclusion Criteria: * Patients who have had any prior therapy for pancreatic cancer * Concurrent chemotherapy or biologic therapy * A history of ataxia telangiectasia or other documented history of radiation hypersensitivity * Scleroderma or active connective tissue disease * Active inflammatory bowel disease * Serious, active infections requiring treatment with IV antibiotics * Uncontrolled intercurrent illness including, but not limited to, psychiatric illness/social situations that would limit compliance with study requirements