177Lu-DOTATATE Modified Delivery Based on Individualized Dosimetry

In order to be eligible to participate in this study, an individual must meet all of the following criteria. A physical, with vital signs, concomitant medication review, and medical history must be completed within 60 calendar days to confirm appropriateness of Lutathera treatment as well as to foundation for listed criteria. Inclusion Criteria: * Provision of signed and dated informed consent form. * Stated willingness to comply with all study procedures and availability for the duration of the study. * Aged ≥ 18 years at time of consent. * Pathologically confirmed (histology or cytology) malignant neoplasm that is determined to be a well-differentiated neuroendocrine tumor (Ki-67 ≤ 20%) with the primary tumor location known or believed to be gastroenteropancreatic origin (GEP-NET) * Disease measuring ≥ 1.5 cm in diameter on CT or MRI as measured per RECIST that shows uptake \> liver background on sstr2 PET/CT with any FDA approved sstr2 imaging agent. SSTR2 PET/CT must have been obtained within 90 days prior to scheduled C1D1 of Lutathera. * Recommended to receive LUTATHERA® therapy for unresectable and/or metastatic neuroendocrine disease. * Adequate performance status (ECOG of 0 or 1; or Karnofsky performance status of ≥70). * Agrees to contraception during therapy. * Neutrophil count within normal limits within 28 days of treatment day 1. * Platelet count within normal limits within 28 days of treatment day 1. * Ability to take oral medication and be willing to adhere to the treatment regimen * For individuals of reproductive potential: agreement to use effective birth control * Agreement to adhere to Lifestyle Considerations throughout study duration: abstain from caffeine or xanthine-containing products as well as alcohol before the start of cycle dosing and through the cycle's final blood sample; minimize social interactions during low blood counts. Exclusion Criteria: * Individuals who are pregnant or lactating (note: potential participants should not engage in 'pump \& dump' strategy; lactation must be discontinued). * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection (requiring inpatient admission or a delay to start of therapy), fever, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. * Surgery, radiation therapy, or chemotherapy ≤ 4 weeks of C1D1 (Toxicities from prior therapies should have resolved to ≤ CTCAE grade 1 or a new baseline established). * Prior peptide-receptor radiotherapy (PRRT). * Therapeutic investigational drug within 4 weeks of C1D1 (imaging agents are acceptable). * A concurrent malignancy that, in the opinion of the investigator, would cause a safety risk by delaying therapy or confound/negatively impact study objectives (documentation of the rationale must be provided) * Prior external beam radiation dose to the kidneys of \>10 Gy (mean dose to functional renal volume). * Prior external beam radiation (including brachytherapy) involving 25% of the bone marrow (excluding scatter doses of ≤ 5 Gy) as estimated by a radiation oncologist. * History of allergic reactions attributed to compounds of similar chemical or biologic composition to Octreoscan® or Netspot™.