177Lu-DOTATATE Modified Delivery Based on Individualized Dosimetry

The goal of this study is to learn if individualized dosimetry-based prescribing of Lutetium-177 DOTATATE (Lutathera, Novartis Pharmaceuticals) improves treatment outcomes for adults with unresectable neuroendocrine tumors. To investigate this, study participants will: * Undergo Somatostatin Receptor (SSTR) positron emission tomography (PET) imaging, such as a DOTATOC PET/CT scan * Be randomized to receive standard treatment (as per FDA guidelines) or investigational treatment (customized dosing of Lutathera based upon dosimetry) * Undergo blood tests for 4 to 8 weeks after each Lutathera treatment * Complete patient reported outcome questionnaires * Visit the clinic for follow-up about every 8 weeks.