title: Inhomogeneous activity distribution of 177Lu-DOTA0-Tyr3-octreotate and effects on somatostatin receptor expression in human carcinoid GOT1 tumors in nude mice.
abstract: The aim of this study was to investigate the activity distribution in neouroendocrine tumors after diagnostic, or therapeutic, amounts of [(177)Lu-DOTA(0)-Tyr(3)]-octreotate and to investigate how the activity distribution influences the absorbed dose. Furthermore, the activity distribution of a second administration of radiolabeled octreotate was studied. Nude mice with subcutaneously grown human midgut carcinoid (GOT1) were injected intravenously with different amounts of (177)Lu-octreotate. At different time points thereafter (4 h to 13 days), a second injection of [(111)In-DOTA(0)-Tyr(3)]-octreotate was given to estimate the somatostatin receptor (sstr) expression. The activity distribution in the tumors was then determined. Monte Carlo simulations with PENELOPE were performed for dosimetry. Fifty-one out of 58 investigated tumors showed a lower activity concentration in the peripheral part than in the central part of the tumor. The amount of activity injected, or time after administration, did neither influence the relative activity nor the sstr distribution in the tumor. After an initial down-regulation (at 4-24 h), there was an up-regulation of sstr (1.5-2 times, at 7-14 days). Monte Carlo simulations demonstrated an inhomogeneous absorbed dose distribution in the tumor using (177)Lu, with twice as high absorbed dose centrally than peripherally. The high activity concentration centrally and the up-regulation of sstr demonstrated will facilitate fractionated therapy using radiolabeled somatostatin analogues if similar results will be obtained also in patients. The inhomogeneous activity distribution in the tumor has to be taken into account when the absorbed dose distribution in tumor is calculated.
authors: Department of Radiation Physics, Lundberg Laboratory for Cancer Research, University of Gothenburg, Sahlgrenska University Hospital, 413 45 Gothenburg, Sweden. jenny.oddstig@skane.se
authors: Jenny
authors: J
authors: Oddstig
authors: Peter
authors: P
authors: Bernhardt
authors: Helena
authors: H
authors: Lizana
authors: Ola
authors: O
authors: Nilsson
authors: Håkan
authors: H
authors: Ahlman
authors: Lars
authors: L
authors: Kölby
authors: Eva
authors: E
authors: Forssell-Aronsson
mesh_terms: D000818:Animals; D002276:Carcinoid Tumor / Q000175:diagnosis* / Q000000981:diagnostic imaging* / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D017599:Neuroectodermal Tumors / Q000175:diagnosis* / Q000000981:diagnostic imaging* / Q000378:metabolism; D015282:Octreotide / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D009942:Organometallic Compounds / Q000008:administration & dosage / Q000493:pharmacokinetics*; D011877:Radionuclide Imaging; D017481:Receptors, Somatostatin / Q000096:biosynthesis*; D014018:Tissue Distribution
chemical_list: D009942:Organometallic Compounds; D017481:Receptors, Somatostatin; C447941:lutetium Lu 177 dotatate; D015282:Octreotide