Gastro-enteropancreatic Neuro-endocrine tumors (GEP-NETs) are rare slow-growing cancers which commonly involve the abdominal organs like liver, stomach, intestines and pancreas. Their incidence has been documented to have increased over the last decade, thus resulting in treatment options being developed to treat these cancers. These cancers spread commonly to the liver, followed by lungs, bones and other sites. Depending on the extent of disease seen on scan, treatment is planned. Patients are advised Peptide Receptor Radionuclide Therapy (PRRT), which is the current standard of treatment for metastatic GEP-NETs. Radio-isotopes labeled to octreotide analogs bind to somatostatin receptors on surface of cancer cells and deliver radiation to the cancer cells when injected into the body. Lu-177 (Lutetium-177) is one such radioisotope which has been used for tagging to the octreotide and is known as Lu-177 DOTATATE PRRT, which is now routinely used in clinical practice. Terbium-161 is another radioisotope which can be labeled to octreotide and used for PRRT. It has advantages over Lu-177 such that it specifically reaches the tumor sites and does not affect the surrounding normal cells, due to its higher penetrating capacity and shorter range of travel. This will benefit patients as the effectiveness of PRRT will be higher with lesser side effects. However, the investigators can only do this by performing a study. Response to treatment can be evaluated by performing scans and side effects, if any can be studied by performing blood tests.