Modified Voxel-Based Multimodel Fitting for Kidney Dosimetry in Lu-177 DOTATATE Therapy M. Buchori Amin Kartani, Assyifa Rahman Hakim, Antonius Fajar Adinegoro and Deni Hardiansyah
Faculty of Mathematics and science, University of Indonesia, Depok, Indonesia
Abstract
This study proposes a modified voxel-based multimodel fitting framework (mVoMM) for voxel-level time-activity curve analysis by incorporating additional model-selection criteria, including the Bayesian Information Criterion (BIC) and coefficient of variation (CV), to identify the optimal function for describing voxel-wise right and left kidney biokinetics. Four-time-point quantitative SPECT/CT datasets from the kidneys of a patient included in the SNMMI Dosimetry Challenge were analyzed. A set of sums-of-exponentials (SOE) functions with two (f2) and three (f3) parameters were individually fitted at the voxel level using four time-point data. Voxels with more than three valid time points were modeled using f3a, f3b, or f3c, while the biexponential model f2 was applied to 2-4 time points when it yielded a lower CV. In mVoMM, model selection was performed using BIC under the constraint of CV under 50% and R square more than equal 0.9, whereas VoMM only used R square more than equal 0.9. Time-integrated activity (TIA) was derived from the selected models and voxel absorbed doses were computed using the voxel S-value convolution method. Performance evaluation between mVoMM and VoMM used relative deviation (RD), root mean square error (RMSE), and mean absolute percentage error (MAPE). For the right kidney, mVoMM showed a mean absorbed dose of 2.54 Gy and maximum dose of 6.83 Gy, whereas VoMM showed 2.63 Gy and 6.07 Gy. The comparison yielded RD of 2.89% +- 13.36%, RMSE of 13.67%, and MAPE of 13.36%. For the left kidney, mVoMM showed a mean absorbed dose of 2.78 Gy and maximum dose of 6.03 Gy, whereas VoMM showed 2.83 Gy and 9.10 Gy, with RD of -4.64% +- 26%, RMSE of 27.161%, and MAPE of 14.11%. This preliminary study demonstrates that mVoMM can provide a systematic framework for patient-specific voxel-level dosimetry.
