Still working on the accompanying paper, so maybe I can get that published somewhere.
This is the abstract that I submitted:
Verification of I-131 Half Life Obtained by Conjugate View Measurements Using Medium and High Energy Collimators
Objective: Residence time measurements obtained by serial whole body conjugate view imaging are commonly used in patient specific dosimetry for radioimmunotherapy (RIT) applications. In order to determine the effect of collimator selection on residence time measurements for I-131, the accuracy of I-131 half-life measurements using multiple gamma camera and collimator combinations was investigated.
Method: Serial anterior and posterior whole body images were acquired over a period of 15 days using 4 different gamma cameras with medium and/or high energy collimators. Background corrected geometric mean counts from the images were fitted to a mono-exponential curve to determine the half-life of I-131 for the different gamma camera/collimator combinations.
Results: An average half-life of 8.15 days with a standard deviation (SD) of 0.07 days was obtained from all camera/collimator combinations. A half life of 8.12 days (SD 0.11 d) was obtained for the high energy collimators, and 8.18 d (SD 0.04 d) for the medium energy collimators. These values are all very close to the 8.021 day I-131 half-life from the NuDat 2.1 database. Similar results were also obtained when looking at the measured half-life for single head gamma camera configurations (mean half life 8.15 d, SD 0.12 d). The variation in the therapeutic I-131-tositumomab dose resulting from the differences in measured half-ilfe ranged between 69.8-70.4 mCi.
Conclusion: There is no significant difference in I-131 half-life and residence time measurements made using medium or high energy collimators in dual head or single head imaging configurations.