THE ACCURACY OF KIDNEY’S TIA CALCULATED FOR THREE TIME POINTS BIOKINETIC DATA OF [177LU]LU-DOTATATE USING MONO-EXPONENTIAL FUNCTION

Abstract

This study evaluates the accuracy of time-integrated activities (TIAs) using different sampling schedules of biokinetic data for [¹⁷⁷Lu]Lu-DOTATATE in kidneys, focusing on three-time points (3TPs) schedules. The biokinetic data were obtained from PMID33443063. The data were collected from six patients using SPECT/CT measurements at four-time points (4TPs) with various combinations of the following time points: T1=(4.2±0.5), T2=(34.9±11.6), T3=(99.8±1.5), T4=(124.3±3.2), and T5=(167.4±19.7) h post-injection. A mono-exponential function was fitted to 4TPs data to calculate reference TIAs (rTIAs). Parameters from this function were refitted to 10 combinations of three data sets to derive three-time points TIAs (3TPTIAs). The root-mean-square error (RMSE) of relative deviation (RD) between 3TPTIAs and rTIAs was analyzed. The sampling schedule for the 3TPs with the lowest RMSE, at 1.19%, was the combination of T1, T2, and T4 hours. On the other hand, all 3TPs fitting combinations excluding T1 were identified as having the highest RMSE, at 17.15%. The best combination of 3TPs was achieved by including T1, T2, and T4. It is important to include T1 when using the mono-exponential function and 3TPs data, as its presence impacts the accuracy of kidney dosimetry for [¹⁷⁷Lu]Lu-DOTATATE therapy. Selecting an optimal schedule of 3TPs enhances kidney dosimetry accuracy.