Dose-Stratified Single Post-Therapeutic Radioiodine Whole-Body Scintigraphy in Differentiated Thyroid Cancer: A Retrospective Evaluation of Diagnostic Accuracy and Optimal Scan Timing

Background: Radioactive iodine (RAI) therapy plays a major role in the treatment of differentiated thyroid cancer (DTC). The optimal time and frequency for performing post-therapeutic whole-body scans (WBS) to detect metastatic lesions are still controversial. Objectives: To evaluate the diagnostic accuracy of a dose-stratified single post- 131 I WBS protocol for detecting metastatic disease in DTC and to determine optimal scan timing across low, intermediate, and high therapeutic dose strata. Materials and Methods: A retrospective cohort study was conducted on DTC patients receiving therapeutic 131I in 2021 at a single tertiary nuclear medicine department. Combined dual-scan findings served as the reference standard. The early WBS (days 2–3) was the index test for patients receiving 3.7 GBq; the delayed WBS (days 5–8) was for those receiving 5.5–7.4 GBq. Two nuclear medicine physicians independently reviewed all scans. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated. Results: 134 DTC patients were analyzed; 82.7% were female with a median age of 38.5 years (IQR: 32–47). The majority (51.5%) received 3.7 GBq, and 87.8% were stimulated with rhTSH (thyrogen). The dose-stratified single-scan protocol achieved a sensitivity of 99.1% and specificity of 100%, demonstrating high diagnostic performance relative to the dual-scan reference standard. Conclusions: A dose-stratified single post-therapeutic WBS demonstrated high diagnostic accuracy in this retrospective single-center cohort. These preliminary findings suggest a single-scan approach may suffice for routine post- 131 I assessment in DTC, reducing hospital visits and radiation exposure. Prospective multicenter validation incorporating thyroglobulin correlation and SPECT/CT is warranted.