This research study is studying an intervention as a possible treatment for pancreatic cancer.

In this research study, the investigators are researching how well IORT during surgery works in treating pancreatic cancer after 3-6 months of chemotherapy and external radiation therapy. IORT works by delivering radiation therapy to the tumor while reducing the amount of healthy tissue exposed to the radiation therapy. The investigators believe that the administration of IORT after 3-6 months of chemotherapy will help to stop the cancer cells from growing.

The FDA (the U.S. Food and Drug Administration) has not approved IORT for this specific disease but it has been approved for other uses.

Inclusion Criteria:

• Age ≥ 18 years
• ECOG Performance Status 0-1
• Previous completion of at least three (3) months of EITHER gemcitabine plus nab-paclitaxel OR FOLFIRINOX (5-fluorouracil, oxaliplatin, irinotecan and leucovorin)
• Previous completion of either stereotactic-body radiation therapy (SBRT) (minimum 24 Gy) or external beam irradiation (EBRT) (minimum 45 Gy)
• Participation in any investigational drug study within 4 weeks preceding the start of study treatment is PERMITTED.
• Women of childbearing potential (WOCBP) must use appropriate method(s) of contraception. WOCBP should use an adequate method to avoid pregnancy for 5 months after IORT.
• Men who are sexually active with WOCBP must use any contraceptive method with a failure rate of less than 1% per year. Men receiving nivolumab and who are sexually active with WOCBP will be instructed to adhere to contraception for a period of 7 months after IORT. Women who are not of childbearing potential, i.e., who are postmenopausal or surgically sterile as well as azoospermic men do not require contraception.
• Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria:

• Evidence of disease progression or distant metastases.
• Pregnant or lactating women
• Treatment for other invasive carcinomas within the last five years who are at greater than 5% risk of recurrence at time of eligibility screening. Carcinoma in-situ and basal cell carcinoma/ squamous cell carcinoma of the skin are allowed.
• Major surgery, excluding laparoscopy, within 4 weeks of the start of study treatment, without complete recovery
• 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.
• An active infection requiring systemic therapy
• Other serious medical conditions that the investigator feels might compromise study participation