Altered biodistribution of somatostatin analogues after first cycle of Peptide receptor radionuclide therapy.

Introduction Peptide receptor radionuclide therapy (PRRT) targeting the somatostatin receptor has emerged as a powerful palliative therapy in metastasized neuroendocrine tumors. A treatment schedule consisting of several administrations of Y-[DOTA]-Tyroctreotide (Y-DOTATOC) is the standard approach. Because long-term renal toxicity is the dose-limiting factor, dosimetry with In-octreotide is performed in all patients. Sequential images are acquired at five different time points, allowing calculation of the biologic effective dose (BED) on the dose-limiting organs, the kidneys, after several cycles of Y-DOTATOC treatment (1 GBq/m per cycle). On the basis of published data, the maximum-tolerated BED after four cycles is fixed at 37 Gy. In our protocol, Ga-DOTATOC positron emission tomography (PET)/computed tomography (CT) and functional magnetic resonance imaging (perfusion and diffusion weighted) performed before and at weeks 7 and 40 are included.