Testing the Addition of An Anti-cancer Drug, M3814 (Peposertib), to the Usual Radiation-Based Treatment (Lutetium Lu 177 Dotatate) for Pancreatic Neuroendocrine Tumors

Inclusion Criteria: * Patients must have histologically or cytologically confirmed well-differentiated neuroendocrine tumor with positive dotatate scan (gallium 68 or copper 64) (as determined by the site principal investigator \[PI\]) within 6 months before enrollment. Lesions on the dotatate scan (gallium 68 or copper 64) are considered positive if the maximum standard uptake value (SUVmax) is \> 2 times the mean standard uptake value (SUVmean) of normal liver parenchyma. Patients must have the gallium 68 or copper 64 dotatate scans available to send for central review before enrollment * Patients must have measurable progressive disease based on RECIST criteria, version 1.1, evidenced with CT/MRI scans obtained within 12 months before enrollment * Failure of at least one prior systemic cancer treatment with somatostatin analogs * No prior exposure to peptide receptor radionuclide therapy * Age \>= 18 years * Eastern Cooperative Oncology Group (ECOG) performance status =\< 2 (Karnofsky \>= 60%) * White blood cell count \>= 2,000/mcL * Absolute neutrophil count \>= 1,000/mcL * Platelets \>= 75,000/mcL * Hemoglobin \>= 8.0 g/dL * Total bilirubin =\< 1.5 x institutional upper limit of normal (ULN) * Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase \[SGOT\])/alanine aminotransferase (ALT) (serum glutamic pyruvic transaminase \[SGPT\]) =\< 3 x institutional ULN * Alkaline phosphatase =\< 3 x institutional ULN * Glomerular filtration rate (GFR) \>= 50 mL…