To achieve this, we plan to perform serial scintigraphic imaging procedures to measure patient specific bone marrow, kidney, and tumor biodistribution and kinetics for 111In Pentetreotide and 131I-MIBG in adults and children with neuroendocrine tumors. Then, using the program we have already developed, we will input the individual dosimetry measures for bone marrow, kidney and tumor to determine the optimal amounts of administered radioactivity for the combination of 131I MIBG plus 90Y DOTATOC or 131I MIBG alone.