Patients will be discharged from the study unit 48-72 hours after infusion with 188Re-PTI-6D2 or later as determined by the Investigator's clinical judgment. Patients will be required to return for post-treatment follow-up visits approximately 2 and 6 weeks (± two days) after infusion for safety monitoring. Ongoing follow-up visits will continue until disease progression every 4 weeks. Tumor measurements will be performed at baseline, and all follow-up visits to assess for tumor response. Patients with unacceptable adverse events will have events followed until resolution.