Fixed dosing will allow each subject to receive three cycles of 90Y-DOTA-tyr3-Octreotide at 50 mCi/m2. Dosimetry will be performed at each of these cycles; the combined dosimetry measurements will be utilized to determine whether or not a fourth cycle will be administered and, if so, what that dose will be. The administration of this additional cycle is conditional upon a) a subject not experiencing a dose-limiting toxicity during any previous cycle and b) meeting all criteria required at study initiation prior to the fourth dose.