title: Effect of calculation method on kidney dosimetry in177Lu-octreotate treatment.
abstract: BACKGROUND
  177Lu-octreotate is an effective treatment modality for patients with metastatic neuroendocrine tumors. The kidney is a critical dose-limiting organ in that modality. We investigated the absorbed doses in the kidney and compared whole kidney volume (WKV) and small (4 cm3) volume of the kidney (SV) methods. We also evaluated a new calculation method that was based on two single photon emission computed tomography/computed tomography (SPECT/CT) scans.
  
  
  METHODS
  Absorbed radiation doses in the kidneys were calculated for 24 patients with neuroendocrine tumors. All patients received four cycles of177Lu-octreotate given at eight-week intervals with a mean activity of 7.1 GBq (range 3.28-8.79 GBq). Absorbed doses and half-lives were calculated by the WKV and SV methods. Dosimetry was determined for the cortex and medulla in the first treatment cycle.
  
  
  RESULTS
  The mean absorbed radiation dose was 0.44 ± 0.15 Gy/GBq for the WKV method and, 0.74 ± 0.28 Gy/GBq for the SV method. Three patients had a 20% increase of the absorbed dose over the four treatment cycles for the WKV method compared to eight patients for the SV method. The mean absorbed dose in the medulla was 0.62 ± 0.27 Gy/GBq, whereas the mean absorbed dose in the cortex was 0.41 ± 0.22 Gy/GBq. Both regions had similar half-lives. Patients who received lower activities for medical reasons still had similar absorbed doses to kidneys compared to those who received the full activities. Our study indicates that absorbed doses can be calculated reliably using two SPECT/CT scans, at 24 and 168 hours after each treatment.
  
  
  CONCLUSIONS
  Absorbed doses in the kidneys from systemic radionuclide therapy that are measured by the WKV method and SV method cannot be directly compared. There were regional differences within kidneys for the uptake of177Lu-octreotate. Two SPECT/CTs are sufficient for kidney dosimetry based on our new calculation method.
authors.affiliation: a Nuclear Medicine , Helsinki University Central Hospital, Cancer Center , Helsinki , Finland.
authors.forename: Jorma
authors.initials: J
authors.lastname: Heikkonen
authors.affiliation: a Nuclear Medicine , Helsinki University Central Hospital, Cancer Center , Helsinki , Finland.
authors.forename: Hanna
authors.initials: H
authors.lastname: Mäenpää
authors.affiliation: b HUS Medical Imaging Center , Helsinki University Central Hospital, Helsinki , Finland.
authors.forename: Eero
authors.initials: E
authors.lastname: Hippeläinen
authors.affiliation: a Nuclear Medicine , Helsinki University Central Hospital, Cancer Center , Helsinki , Finland.
authors.forename: Vappu
authors.initials: V
authors.lastname: Reijonen
authors.affiliation: c Department of Radiotherapy , Helsinki University Central Hospital, Cancer Center , Helsinki , Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Tenhunen
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006207:Half-Life; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging / Q000528:radiation effects*; D008297:Male; D008875:Middle Aged; D060787:Neoplasm Grading; D018358:Neuroendocrine Tumors / Q000473:pathology / Q000532:radiotherapy*; D015282:Octreotide / Q000031:analogs & derivatives* / Q000627:therapeutic use; D011829:Radiation Dosage; D011868:Radioisotopes / Q000627:therapeutic use*; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D000072098:Single Photon Emission Computed Tomography Computed Tomography
chemical_list: C554548:177Lu-octreotate; D011868:Radioisotopes; D015282:Octreotide