Is detection of additional lesions in post-peptide receptor radionuclide therapy scans with respect to diagnostic imaging only due to different affinity of ligands?: a report of discordance between diagnostic and posttherapy imaging using the same ligand.

It is known that different affinity profiles for somatostatin receptor subtypes among different radiopharmaceuticals result in different organ and tumor uptakes and even in different sensitivities in the detection of lesions. Such differences are considered main factors explaining cases of detecting additional lesions in posttherapy scans with respect to diagnostic imaging. We show a posttherapy scan revealing more lesions-namely, a diffuse bone involvement with many small focal bony uptake areas-than the diagnostic scan using the same radiopharmaceutical (In-111-pentetreotide) in a 71-year-old man with metastases from a well-differentiated ileal neuroendocrine tumor.