title: [(111)In]DOTATOC as a dosimetric substitute for kidney dosimetry during [(90)Y]DOTATOC therapy: results and evaluation of a combined gamma camera/probe approach.
abstract: OBJECTIVE
  During [(90)Y]DOTATOC therapy, for determination of kidney doses a conventional approach using co-injected [(111)In]DOTATOC was evaluated for validity, reliability and reproducibility as well as for the influence of methodological variations and bremsstrahlung. Biologically effective doses were estimated by calculating the relative effectiveness (RE) of kidney doses.
  
  
  METHODS
  Fractionated [(90)Y]DOTATOC therapy (n=20 patients, 3.1+/-0.7 GBq/therapy cycle, 45 therapy cycles) included co-injection of 157+/-37 MBq [(111)In]DOTATOC and a nephroprotective infusion regimen. From serial gamma camera/probe measurements, individual region of interest (ROI) sets were established and kidney doses were determined according to MIRDOSE3 (corrected for individual kidney mass) by use of three methodological variants: (1) correction for interfering organs (liver/spleen) and background activity, (2) correction for interfering organs alone and (3) no corrections. A phantom study was performed with (111) In alone and with (111)In +(90)Y to estimate the influence of (90)Y bremsstrahlung.
  
  
  RESULTS
  Mean kidney dose (method 1, n=20 patients, 20 therapy cycles) was 1.51+/-0.60 Gy/GBq [(90)Y]DOTATOC (1.41+/-0.48 Gy/GBq for n=20 patients, 45 therapy cycles). With partial correction (method 2) or no correction (method 3) for interfering activity, kidney doses increased significantly, to 2.71+/-1.26 Gy/GBq and 3.15+/-1.22 Gy/GBq, respectively. The span of REs ranged from 1.02 to 1.24. Inter-observer variability was as high as +/-32% (+/-2SD). (90)Y bremsstrahlung accounted for a 4-11% underestimation of obtained target activity.
  
  
  CONCLUSIONS
  The obtained kidney doses are highly influenced by methodological variations. Full correction for interfering activity clearly underestimates kidney doses. By comparison, (90)Y bremsstrahlung and variability in the relative effectiveness of kidney doses cause minor bias. Inter-observer variability must be considered when interpreting kidney doses.
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: Sylvia
authors.initials: S
authors.lastname: Schachoff
authors.forename: Ambros
authors.initials: A
authors.lastname: Beer
authors.forename: Anna
authors.initials: A
authors.lastname: Winter
authors.forename: Hans Jürgen
authors.initials: HJ
authors.lastname: Wester
authors.forename: Klemens
authors.initials: K
authors.lastname: Scheidhauer
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
authors.forename: Ingo
authors.initials: I
authors.lastname: Wolf
mesh_terms: D005260:Female; D015902:Gamma Cameras; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015282:Octreotide / Q000031:analogs & derivatives* / Q000032:analysis / Q000627:therapeutic use; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000032:analysis / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D012680:Sensitivity and Specificity
chemical_list: C507387:111In-DOTA-TOC; D019275:Radiopharmaceuticals; C496730:90Y-octreotide, DOTA-Tyr(3)-; D015282:Octreotide