Testing Higher Dose Radiation Therapy for Locally Advanced Pancreatic Cancer

Inclusion Criteria: * At time of enrollment, the patient must have received 4-8 months of active chemotherapy with FOLFIRINOX or NALIRIFOX or gemcitabine/nab-paclitaxel. Patients are permitted to receive more than 1 type of chemotherapy for reasons other than radiographic progression by Response Evaluation Criteria in Solid Tumors (RECIST) (i.e. chemotherapy regimen switch is allowed for toxicity, and/or switch is allowed for toxicity and/or CA19-9 level not declining). Patients are allowed to receive chemotherapy after restaging scans, as long as 1) restaging scans are performed after at least 4 months of chemotherapy and 2) the total chemotherapy duration does not exceed 8 months * "Active chemotherapy" refers to time on chemotherapy not counting treatment breaks (i.e. if a patient had 1 month of chemotherapy followed by 1 month break, this would count as 1 month chemotherapy). Study registration must occur within 45 days of last day of pre-study entry chemotherapy * BASELINE PRE-ENTRY CHEMOTHERAPY REQUIREMENTS: * Pathologically (histologically or cytologically) proven diagnosis of pancreatic ductal adenocarcinoma * Locally advanced unresectable disease (as defined per the National Comprehensive Cancer Network \[NCCN\] guidelines and institutional tumor board review) * Patients must have baseline pre-chemotherapy scans for staging. Options include: CT chest/abdomen/pelvis, CT chest/MRI abdomen/pelvis, CT chest/CT pelvis/MRI abdomen, or PET/CT performed prior to enrollment * Age ≥ 18 years * Performance status Eastern Cooperative Oncology Group (ECOG) 0-2 * Required initial laboratory values: All laboratory values must be obtained any time prior to initiation of chemotherapy up to 30 days post initiation of chemotherapy * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 x upper limit of normal (ULN) * BASELINE CA19-9 AND BILIRUBIN REQUIREMENTS: The purpose is to obtain a baseline CA19-9 in the setting of a normal (or close to normal) bilirubin, since serologic response by serial CA19-9 measurements is part of post-chemotherapy eligibility criteria * If baseline CA19-9 \> 37 U/mL the concurrent bilirubin must be ≤ 1.5 x ULN. (Note: if the bilirubin is not ≤ 1.5 x ULN both the CA19-9 and concurrent bilirubin can be repeated until bilirubin is ≤ 1.5 x ULN, as long as done within specified timeframe \[up to 30 days post chemotherapy initiation\]) * If baseline CA19-9 U/mL ≤ 37, there are no restrictions on the required concurrent bilirubin level, and this can be the accepted baseline value * Prior radiation treatment * Has the patient had prior radiotherapy to the region of the study cancer that would result in overlap of radiation therapy fields * Prior non-overlapping radiation (e.g., breast, head and neck, extremity) is permitted * If uncertain about prior overlap, please contact the study principal investigator, Dr. Nina Sanford * POST PRE-ENTRY CHEMOTHERAPY REQUIREMENTS: * If baseline CA19-9 is elevated (defined as \> 37 u/mL) the post-pre-entry chemotherapy CA19-9 must be less than 200 u/mL OR a 70% decline from pre-chemotherapy level (i.e. a patient with post induction chemotherapy CA199 value ≥ 200 u/mL would qualify, as long as they had at least 70% drop from baseline CA199 value; similarly, a patient with less than a 70% decline would qualify as long as absolute value post induction chemotherapy is under 200 u/mL) (must be completed any time post month 4 of chemotherapy and prior to study entry) * If baseline CA19-9 is not elevated (defined as ≤ 37 u/mL) the post-pre-entry chemotherapy CA19-9 must remain ≤ 37 u/mL (must be completed any time post month 4 of chemotherapy and prior to study entry) * No active duodenal or gastric ulcers * No direct tumor invasion of the bowel or stomach * Restaging scans showing at least stable disease (no progression). Options for scans include: CT chest/abdomen/pelvis, CT chest/MRI abdomen/pelvis, or CT chest/CT pelvis/MRI abdomen, or PET/CT performed prior to enrollment, with restaging CT showing at least stable disease * Not pregnant and not nursing * No cardiac condition that was the primary reason for hospitalization in the last 6 months * New York Heart Association Functional Classification II or better (NYHA Functional Classification III/IV are not eligible) (Note: Patients with known history or current symptoms of cardiac disease, or history of treatment with cardiotoxic agents, should have a clinical risk assessment of cardiac function using the New York Heart Association Functional Classification.) * HIV-infected patients on effective anti-retroviral therapy with undetectable viral load within 6 months are eligible for this trial