¹³¹I therapy for benign thyroid disease: flexible single-time-point dosimetry using population-based model selection...

Area of Science:

• Nuclear Medicine
• Medical Physics
• Endocrinology

Background:

• Accurate dosimetry is crucial for effective radioiodine therapy.
• Single-time-point (STP) methods for estimating time-integrated activity (TIA) offer potential efficiency gains over multi-time-point approaches.
• Nonlinear mixed-effects modeling (NLMEM) combined with population-based model selection (PBMS) provides a robust framework for pharmacokinetic analysis.

Purpose of the Study:

• To evaluate the accuracy of STP TIA estimation using NLMEM and PBMS in patients with benign thyroid disease.
• To compare different STP dosimetry approaches, including those based on the EANM SOP.
• To identify the optimal time point for STP dosimetry in this patient cohort.

Main Methods:

• Collected biokinetic data of iodine-131 (131I) from 73 patients with benign thyroid conditions.
• Utilized NLMEM with PBMS to identify the best sum-of-exponentials function (SOEF) with four parameters.
• Applied NLMEM-based STP dosimetry at various time points and compared results with reference TIAs derived from full NLMEM fits.

Main Results:

• The optimal time point for STP dosimetry was found to be 120 hours post-administration.
• At 120 hours, the NLMEM-based STP TIA estimation (s1TIA) using the best SOEF model showed low deviations (mean RD 2% ± 4%, RMSE 4%, MAPE 3%, %RD5 25%, %RD10 0%).
• The EANM SOP approach (hTIA) at 120 hours resulted in higher deviations (mean RD -3% ± 5%, RMSE 6%, MAPE 5%, %RD5 55%, %RD10 0%).

Conclusions:

• NLMEM with PBMS and the best SOEF model provides satisfactory and reasonable STP estimates for 131I TIA in benign thyroid disease.
• The s1TIA method generally yielded better TIA estimates than the EANM SOP's hTIA.
• STP dosimetry using NLMEM with the EANM SOP SOEF (s2TIAs) was inferior to the hTIA approach.