title: [123I]Mtr-TOCA, a radioiodinated and carbohydrated analogue of octreotide: scintigraphic comparison with [111In]octreotide.
abstract: OBJECTIVE
  Scintigraphy with maltotriose-[123I]Tyr3-octreotate ([123I]Mtr-TOCA) is compared with [111In]DTPA-Phe1-octreotide ([111In]OC) to assess the differences in pharmacokinetics and imaging properties as well as to estimate the therapeutic potential of the corresponding [131I]Mtr-TOCA.
  
  
  METHODS
  Six patients with somatostatin receptor (sstr)-positive tumours were assessed using a dual-head gamma camera. After injection of 137 +/- 28 MBq [123I]Mtr-TOCA, dynamic data acquisition of the upper abdomen (30 min) was performed followed by whole-body scans at 0.5 h, 1 h, 3 h and 20 h as well as by SPECT imaging (tumour) at 2 h. [111In]OC scintigraphy was performed by acquiring whole-body scans (4 h, 24 h) and SPECT (24 h). Using a region of interest (ROI) method, tissue and tumour bound activity was assessed and dosimetry performed.
  
  
  RESULTS
  [123I]Mtr-TOCA shows rapid tumour uptake. Up to 4 h, tumour/organ (tu/org) ratios are stable and generally higher than with [111In]OC. From 3 h to 20 h, tu/org ratios increase for spleen, remain stable for liver and decrease significantly for all other tissues. In contrast, with [111In]OC, tu/org ratios decrease slightly between 4 h and 24 h for liver, spleen and kidney and increase for all other tissues. On [123I]Mtr-TOCA scintigraphy, a total of 27 lesions are detected, whereas 33 lesions are detected on [111In]OC scintigraphy (p=0.50). Effective patient absorbed dose is 1.9 +/- 0.9 mSv per 100 MBq [123I]Mtr-TOCA.
  
  
  CONCLUSIONS
  Compared with [111In]OC, [123I]Mtr-TOCA enables faster imaging of sstr-positive tumours with a lower radiation burden to the patient. [123I]Mtr-TOCA and [111In]OC allow for tumour imaging with almost identical contrast and diagnostic yield. As regards peptide receptor radionuclide therapy, radioiodinated Mtr-TOCA is hampered by limited intratumoural activity retention
authors.affiliation: Department of Nuclear Medicine, Technische Universität München, Klinikum rechts der Isar, Ismaninger Strasse 22, 81675 Munich, Germany. a.stahl@lrz.tum.de
authors.forename: Alexander
authors.initials: A
authors.lastname: Stahl
authors.forename: Günther
authors.initials: G
authors.lastname: Meisetschläger
authors.forename: Margret
authors.initials: M
authors.lastname: Schottelius
authors.forename: Kjerstin
authors.initials: K
authors.lastname: Bruus-Jensen
authors.forename: Ingo
authors.initials: I
authors.lastname: Wolf
authors.forename: Klemens
authors.initials: K
authors.lastname: Scheidhauer
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
mesh_terms: D006801:Humans; D008657:Metabolic Clearance Rate; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging* / Q000378:metabolism*; D015282:Octreotide / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D009928:Organ Specificity; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D017481:Receptors, Somatostatin / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D014312:Trisaccharides / Q000493:pharmacokinetics*; D051598:Whole Body Imaging / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D017481:Receptors, Somatostatin; D014312:Trisaccharides; C094279:indium-111-octreotide; C447834:octreotate, maltotriose-iodotyrosyl(3)-; D015282:Octreotide