A First-in-human Clinical Trial to Evaluate an Alpha-radiation Imaging Agent

Inclusion Criteria: * Ability to understand and willingness to provide informed consent * Stated willingness to comply with all study procedures and availability for duration of study * Aged ≥ 18 years at the time of study drug administration * Pathologically confirmed (histology or cytology) well-differentiated neuroendocrine tumor (WHO Grade 1 or 2) with primary location known or believed to be midgut or foregut * At least 1 somatostatin receptor positive tumor site as demonstrated by PET/CT study utilizing an FDA approved PET agent within 12 months of consent * ≥1 evaluable site of disease measuring ≥ 2.0 cm in any dimension on CT or MRI * Adequate performance status (ECOG of 0 or 1; or KPS of ≥70). * Not experiencing an uncontrolled intercurrent illness such as: infection requiring inpatient admission, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, psychiatric illness/social situations, or any other condition that would limit compliance with study requirements as determined by study team members. Exclusion Criteria: * Individuals who are pregnant or breast feeding. A pregnancy test will be administered to individuals of child-bearing potential (per institutional policies) at screening. Individuals must agree to pregnancy tests prior to each administration of a radionuclidic agent for this study. * Individuals of reproductive potential who decline to use effective contraception through the study (22 days equaling 10 half-lives). * Lactating individuals who decline to withhold breastfeeding their child. As the effects of \[203Pb\]VMT-α-NET on the infant are unknown and relatively long half-life, women may not resume breast feeding for the current child. * Therapeutic investigational drug within 4 weeks of C1D1 * Patients for whom, in the opinion of their physician, a 24-hour discontinuation of somatostatin analogue therapy represents a health risk. * Subject's weight exceeds the limit of the imaging system. * Long-acting somatostatin analogue treatment ≤ 20 days of C1D1 * History of allergic reactions attributed to compounds of similar chemical or biologic composition to \[90Y\]DOTA-tyr3-Octreotide, Octreoscan®, or \[68Ga\]Octreotide.