MR Guided Phase II Radiotherapy Dose Escalation in Unresectable Non-Metastatic Pancreatic Cancer

Inclusion Criteria: * Pathologically confirmed (histologic or cytologic), locally advanced, adenocarcinoma of the pancreas; patients must have unresectable disease based on institutional standardized criteria of unresectability or medical inoperability. * Participants with and without regional adenopathy are eligible. * No distant metastases, based upon the following minimum diagnostic workup: * History/physical examination, including collection of weight and vital signs, within 28 days prior to study entry; * Abdominal/pelvic CT scan with IV contrast within 21 days prior to study entry; * Chest CT scan, or X-ray within 21 days prior to study entry. * Abdominal/pelvic MR prior to radiation with perfusion and diffusion- weighted sequences and MR and CT sim for radiation planning Pet scan within 21 days prior to study entry, Functional renal study. * Zubrod performance status 0-1 within 1 week of study entry. * Age ≥ 18. * Hematology and cancer antigen (CA) 19-9 / carcinoembryonic antigen (CEA) within 14 days prior to study entry, as follows. * Absolute neutrophil count (ANC) ≥ 1,500 cells/mm\^3; * Platelets ≥ 100,000 cells/mm\^3; * Hemoglobin ≥ 8.0 g/dl (Note: The use of transfusion or other intervention to achieve Hgb ≥ 8.0 g/dl is acceptable.); * Serum creatinine ≤ 1.5 mg/dl; * Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \< 3 x upper limit of normal (ULN); * Total bilirubin \< 3.0 mg/dL; * Alkaline phosphatase \< 3 x ULN; * Fasting blood glucose \< 160 mg/dl. * Negative serum pregnancy test (if applicable) within 14 days prior to study entry. * Ability to swallow oral medications. * Participants must have had at least 4 months of prior systemic chemotherapy. * Participants must provide study specific informed consent prior to study entry. * Women of childbearing potential and male participants who are sexually active must practice adequate contraception. Exclusion criteria: * Distant metastatic disease, second malignancy or peritoneal seeding; * Prior invasive malignancy (except non-melanomatous skin cancer) unless disease free for a minimum of 3 years (For example, carcinoma in situ of the breast, oral cavity, or cervix are all permissible). * Prior radiotherapy to the region of the study cancer that would result in overlap of radiation therapy fields. * Any major surgery within 28 days prior to study entry * Severe, active co-morbidity, defined as follows: * Unstable angina and/or congestive heart failure requiring hospitalization within the last 6 months; * Transmural myocardial infarction within 3 months prior to study entry; * Acute bacterial or fungal infection requiring intravenous antibiotics at the time of registration; * Chronic obstructive pulmonary disease exacerbation or other respiratory illness requiring hospitalization or precluding study therapy within 30 days before registration; * Uncontrolled malabsorption syndrome significantly affecting gastrointestinal function; * Any unresolved bowel or bile duct obstruction; * Major resection of the stomach or small bowel that could affect the absorption of capecitabine * Acquired immune deficiency syndrome (AIDS) based upon current Center for Disease Control (CDC) definition; * Pregnancy or women of childbearing potential and men who are sexually active and not willing/able to use medically acceptable forms of contraception during the course of the study and for women, for 3 months after the last study drug administration. * Women who are lactating at the time of registration and who plan to be lactating through 3 months after the last study drug administration. * Prior allergic reaction to capecitabine or gemcitabine * Inability to undergo an MR of the abdomen/pelvis * Participation in another clinical treatment trial while on study.