title: Patient-specific radiation dosimetry of 99mTc-HYNIC-Tyr3-octreotide in neuroendocrine tumors.
abstract: (99m)Tc-hydrazinonicotinamide-Tyr(3)-octreotide ((99m)Tc-HYNIC-TOC) is increasingly gaining acceptance as a new radiopharmaceutical for the diagnosis of pathologic lesions overexpressing somatostatin receptors. However, little information has been published about the radiation dosimetry of this agent. The aim of this study was to assess the biodistribution and radiation dosimetry of commercially available (99m)Tc-HYNIC-TOC. A dose calculation procedure designed to be feasible to implement in a busy clinical environment was used.
  
  
  METHODS
  Twenty-eight patients were imaged for suspected neuroendocrine tumors using a series of whole-body planar, dynamic planar, and SPECT/CT studies, after injection with (99m)Tc-HYNIC-TOC. Patient-specific dosimetry was performed using the OLINDA/EXM software with time-integrated activity coefficients estimated from a hybrid planar/SPECT technique. A phantom experiment was performed to establish adaptive thresholds for determination of source region volumes and activities.
  
  
  RESULTS
  Pathologic uptake, diagnosed as due to neuroendocrine tumors, was observed in 12 patients. Normal organs with significant uptake included the kidneys, liver, and spleen. The mean effective dose after (99m)Tc-HYNIC-TOC injection was 4.6 ± 1.1 mSv. Average normal-organ doses were 0.030 ± 0.012, 0.021 ± 0.007, and 0.012 ± 0.005 mGy/MBq for the spleen, kidneys, and liver, respectively. The interpatient kidney dose ranged from 0.011 to 0.039 mGy/MBq, whereas the range of tumor doses varied from 0.003 to 0.053 mGy/MBq. The ratio of tumor to kidney dose ranged from 0.13 to 2.9. The optimal thresholds for recovery of true activity in the phantom study were significantly lower than those used for volume determination.
  
  
  CONCLUSIONS
  The patient-specific 3-dimensional dosimetry protocol used in this study is a clinically feasible technique that has been applied to demonstrate large dose variations in tumors and normal organs between patients imaged with (99m)Tc-HYNIC-TOC.
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada. grimes@physics.ubc.ca
authors.forename: Joshua
authors.initials: J
authors.lastname: Grimes
authors.forename: Anna
authors.initials: A
authors.lastname: Celler
authors.forename: Bozena
authors.initials: B
authors.lastname: Birkenfeld
authors.forename: Sergey
authors.initials: S
authors.lastname: Shcherbinin
authors.forename: Maria H
authors.initials: MH
authors.lastname: Listewnik
authors.forename: Hanna
authors.initials: H
authors.lastname: Piwowarska-Bilska
authors.forename: Renata
authors.initials: R
authors.lastname: Mikolajczak
authors.forename: Piotr
authors.initials: P
authors.lastname: Zorga
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D005260:Female; D006207:Half-Life; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging*; D015282:Octreotide / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D009928:Organ Specificity; D015609:Organotechnetium Compounds / Q000008:administration & dosage* / Q000493:pharmacokinetics; D019047:Phantoms, Imaging; D011874:Radiometry; D019275:Radiopharmaceuticals / Q000008:administration & dosage* / Q000493:pharmacokinetics; D017481:Receptors, Somatostatin / Q000378:metabolism; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon; D051598:Whole Body Imaging; D055815:Young Adult
chemical_list: D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D017481:Receptors, Somatostatin; C410263:technetium Tc 99m hydrazinonicotinyl-Tyr(3)-octreotide; D015282:Octreotide