INCLUSION CRITERIA

* Histologically-confirmed adenocarcinoma of the pancreas
* Determined unresectable by a pancreatic cancer surgeon or a multi-disciplinary or gastrointestinal oncology Tumor Board.
* Stable or better disease on re-staging scans
* Typically, tumors < 8.0 cm in greatest axial dimension but final determination of eligibility based upon radiation normal tissue constraints
* Eastern Cooperative Oncology Group (ECOG) Performance Status 0, 1, or 2
* Leukocytes (white blood cells, WBC) ≥ 3,000/mL
* Absolute neutrophil count (ANC) ≥ 1,500/mL
* Platelets ≥ 50,000/mL
* Total bilirubin ≤ 1.5 X institutional upper limit of normal (ULN)
* Aspartate aminotransferase (AST) / alanine aminotransferase (ALT) ≤ 2.5 X institutional ULN
* Creatinine within normal institutional limits
* Ability to understand and the willingness to sign an informed consent form
* Life expectancy > 6 months

EXCLUSION CRITERIA

* Metastatic disease
* Prior radiotherapy to the upper abdomen/liver.
* Prior chemotherapy for pancreatic cancer, other than up to 4 cycles of modified FOLFIRINOX.
* Age < 18 years
* Uncontrolled intercurrent illness including, but not limited to:

* Ongoing or active infection (or infections requiring systemic antibiotic treatment)
* Symptomatic congestive heart failure
* Unstable angina pectoris
* Cardiac arrhythmia
* Psychiatric illness/social situations that would limit compliance with study requirements.
* Any concurrent malignancy other than non-melanoma skin cancer, non-invasive bladder cancer, or carcinoma in situ of the cervix. Patients with a previous malignancy without evidence of disease for > 5 years will be allowed to enter the trial.
* Pregnant or lactating
* Women of child-bearing potential who are unwilling or unable to use an acceptable method of birth control (hormonal or barrier method of birth control; abstinence) for duration of the study
* Women who are not post-menopausal (as defined in Appendix III) and have a positive urine or serum pregnancy test or refuse to take a pregnancy test
* Male subjects who are unwilling or unable to use effective contraception for duration of the study