Biodistribution of 188Re-PTI-6D2 will be evaluated by whole body imaging with a gamma camera immediately after infusion (0 - 2 hrs.), at 2.5 - 5 hours, at 6 - 8 hours, and 24 hours post-infusion. Whole body imaging at 48 and 72 hours post-infusion may be conducted at the discretion of the PI. Urine will be collected to measure cumulative radioactivity excretion up to 48-72 hours post-infusion (depending on the hospital discharge date). Pharmacokinetics of the mAb and radioactivity will be determined from blood samples taken through 48-72 hours post-infusion (depending on the hospital discharge date). Dosimetry calculations will be performed to determine estimated absorbed radiation doses to critical organs and to tumor.