title: Differences in predicted and actually absorbed doses in peptide receptor radionuclide therapy.
abstract: OBJECTIVE
  An important assumption in dosimetry prior to radionuclide therapy is the equivalence of pretherapeutic and therapeutic biodistribution. In this study the authors investigate if this assumption is justified in sst2-receptor targeting peptide therapy, as unequal amounts of peptide and different peptides for pretherapeutic measurements and therapy are commonly used.
  
  
  METHODS
  Physiologically based pharmacokinetic models were developed. Gamma camera and serum measurements of ten patients with metastasizing neuroendocrine tumors were conducted using (111)In-DTPAOC. The most suitable model was selected using the corrected Akaike information criterion. Based on that model and the estimated individual parameters, predicted and measured (90)Y-DOTATATE excretions during therapy were compared. The residence times for the pretherapeutic (measured) and therapeutic scenarios (simulated) were calculated.
  
  
  RESULTS
  Predicted and measured therapeutic excretion differed in three patients by 10%, 31%, and 7%. The measured pretherapeutic and therapeutic excretion differed by 53%, 56%, and 52%. The simulated therapeutic residence times of kidney and tumor were 3.1 ± 0.6 and 2.5 ± 1.2 fold higher than the measured pretherapeutic ones.
  
  
  CONCLUSIONS
  To avoid the introduction of unnecessary inaccuracy in dosimetry, using the same substance along with the same amount for pretherapeutic measurements and therapy is recommended.
authors.affiliation: Klinik für Nuklearmedizin, Universität Ulm, Ulm, Germany. peter.kletting@uniklinik-ulm.de
authors.forename: Peter
authors.initials: P
authors.lastname: Kletting
authors.forename: Berthold
authors.initials: B
authors.lastname: Muller
authors.forename: Bahar
authors.initials: B
authors.lastname: Erentok
authors.forename: Jorn
authors.initials: J
authors.lastname: Schmaljohann
authors.forename: Florian F
authors.initials: FF
authors.lastname: Behrendt
authors.forename: Sven N
authors.initials: SN
authors.lastname: Reske
authors.forename: Felix M
authors.initials: FM
authors.lastname: Mottaghy
authors.forename: Gerhard
authors.initials: G
authors.lastname: Glatting
mesh_terms: D006801:Humans; D008954:Models, Biological; D018358:Neuroendocrine Tumors / Q000378:metabolism* / Q000532:radiotherapy*; D015282:Octreotide / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics / Q000627:therapeutic use; D009942:Organometallic Compounds / Q000493:pharmacokinetics / Q000627:therapeutic use; D004369:Pentetic Acid / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics / Q000627:therapeutic use; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D017481:Receptors, Somatostatin / Q000378:metabolism*
chemical_list: C539274:90Y-octreotate, DOTA(0)-Tyr(3)-Thr(8)-; D009942:Organometallic Compounds; D017481:Receptors, Somatostatin; C106140:somatostatin receptor sst2A; C071632:SDZ 215-811; D004369:Pentetic Acid; D015282:Octreotide