[(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.
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.
Stahl
Alexander
A
Department of Nuclear Medicine, Technische Universität München, Klinikum rechts der Isar, Ismaninger Strasse 22, 81675 Munich, Germany. a.stahl@lrz.tum.de
Schachoff
Sylvia
S
Beer
Ambros
A
Winter
Anna
A
Wester
Hans Jürgen
HJ
Scheidhauer
Klemens
K
Schwaiger
Markus
M
Wolf
Ingo
I
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
C507387:111In-DOTA-TOC; D019275:Radiopharmaceuticals; C496730:90Y-octreotide, DOTA-Tyr(3)-; D015282:Octreotide