Influence of radiation source geometry on determination of (111)In and (90)Y activity of radiopharmaceuticals.
OBJECTIVE
Yttrium-90 (Y)-labelled peptides such as DOTATOC and antibodies such as Zevalin are widely used in radionuclide therapy. Indium-111 (In) is used as a Y surrogate for imaging and dosimetry purposes. We aimed to investigate accuracy, geometry (vials and syringes) and volume dependencies for both radionuclides in several different radionuclide calibrators.


METHODS
YCl3 and InCl3 solutions were gravimetrically dispensed into the most frequently used containers. In each container several dilutions of the parent solutions were performed. Mass, activity and time were recorded for each calibrator and measurement. Aliquots of both parent solutions were calibrated at the National Metrology Laboratory, Vienna, Austria (BEV). From our measurements and results from BEV, correction factors were determined and further partitioned into calibration, geometry and volume correction factors.


RESULTS
Using the nominal calibration factors provided by the manufacturer, measured activity in P6 vials was overestimated by up to 25% for In, depending on the calibrator. Y activity was either underestimated (by up to 20%) or overestimated (by up to 25%) using different radionuclide calibrators. This is the result of the difference in containers used to set the manufacturer's calibration factor values and the containers used in nuclear medicine departments and in this study. There was little geometry dependence for glass vials but strong geometry dependence for syringes for both radionuclides in all calibrators.


CONCLUSIONS
The results should constitute a warning for all personnel responsible for preparation of radiopharmaceuticals. Every nuclear medicine department should incorporate a proper quality-control regimen for radionuclide calibrators and a quality-assurance system.
Peitl
Petra Kolenc
PK
Department for Nuclear Medicine, University Medical Centre Ljubljana, Zaloska bUniversity of Ljubljana, Faculty of Pharmacy, Askerceva, 1000 Ljubljana, Slovenia. petra.peitl@kclj.si
Tomse
Petra
P
Kroselj
Marko
M
Socan
Aljaz
A
Hojker
Sergej
S
Pecar
Slavko
S
Stopar
Tanja Gmeiner
TG
D007205:Indium Radioisotopes / Q000032:analysis*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods* / Q000592:standards*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D017524:Slovenia; D013048:Specimen Handling / Q000379:methods* / Q000592:standards*; D015021:Yttrium Radioisotopes / Q000032:analysis*
D007205:Indium Radioisotopes; D015021:Yttrium Radioisotopes