Collimator selection, acquisition speed, and visual assessment of 131I-tositumomab biodistribution in a phantom model.
(131)I-Tositumomab has been used in treating patients with non-Hodgkin's lymphoma. It is generally recommended that high-energy collimators be used to image patients before they receive (131)I-tositumomab therapy, to determine the effective half-life for therapeutic dose and gross biodistribution. Because many nuclear medicine departments do not possess high-energy collimators, this study was designed to assess the suitability of using medium-energy collimators. The effect of scanning speed was also investigated, in an attempt to optimize the acquisition time.


METHODS
Measurements were taken using an elliptic anthropomorphic torso phantom and an organ-scanning phantom fitted with fillable spheres (1-5 cm in diameter) and organ inserts. Three phantom studies were performed with differing initial (131)I concentrations in the organs, the spheres, and the thoracic and abdominal chambers. Images were acquired with both high-energy and medium-energy collimators and at acquisition speeds of 20 and 100 cm/min. The half-life for each combination (study/collimator/speed) was calculated from a linear fit of the data. The contrast of the tumor sphere was assessed using 2 identical regions, placed on and beside the sphere, and averaged over several time points. Biodistribution and image quality were visually assessed by 2 independent observers.


RESULTS
Measured half-life values and visual assessment of biodistribution showed no significant difference between the 2 collimators (P = 0.32) or acquisition speeds (P = 0.85). A significant difference in the contrast of the tumor spheres was observed between the 2 collimators (P < 0.01) but not between acquisition speeds. Visual assessment of the images showed increased noise on the image acquired at 100 cm/min, although this noise did not affect lesion detectability.


CONCLUSIONS
Measured half-life is not significantly different between the 2 collimators; hence, calculation of the residence time would be nearly the same. Medium-energy collimators can be used to accurately calculate the (131)I-tositumomab therapeutic dose and detect alterations in biodistribution.
Tan
Hung K
HK
Division of Nuclear Medicine, Ottawa Hospital, Ottawa, Ontario, Canada.
Wassenaar
Richard W
RW
Zeng
Wanzhen
W
D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics* / Q000627:therapeutic use; D001822:Body Burden; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008228:Lymphoma, Non-Hodgkin / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000532:radiotherapy; D008657:Metabolic Clearance Rate; D009928:Organ Specificity; D019047:Phantoms, Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics / Q000627:therapeutic use; D012062:Relative Biological Effectiveness; D013997:Time Factors; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation / Q000379:methods; D051598:Whole Body Imaging; D014915:Whole-Body Counting / Q000379:methods*
D000911:Antibodies, Monoclonal; D019275:Radiopharmaceuticals; C119496:tositumomab I-131