6-Deoxy-6-[ 18 F]Fluoro-L-Ascorbic Acid PET/CT in the Detection of Lymph Node Metastases for Postoperative Differentiated Thyroid Cancer Patients : Using Histopathology as Reference Standard.

Background: 6-Deoxy-6-[ 18 F]fluoro-L-ascorbic acid ([ 18 F]FAA) is a radioisotope-labeled analogue of ascorbic acid (AA), designed to investigate oxidative stress and AA accumulation in vivo by PET imaging. It has also been reported as a promising radiotracer for tumor detection, particularly in metastatic differentiated thyroid cancer (DTC).

Purpose: This study aimed to evaluate the diagnostic potential of [ 18 F]FAA in detecting lymph node metastases in postoperative DTC patients.

Methods: Patients who have undergone thyroidectomy for DTC and are either preparing for 131 I therapy or undergoing follow-up examinations were prospectively enrolled and underwent [ 18 F]FAA PET/CT from September 2023 to November 2023. Histopathologic results served as gold standard for final diagnosis.

Results: A total of 70 patients [mean age, 40.5 y±12.0 (SD); 23 men] with pathologically confirmed DTC were enrolled. At patient-based analysis, [ 18 F]FAA PET/CT detected positive lymph nodes in all patients, with an accuracy of 92.9% (65/70). At lesion-based analysis of patients who underwent central and/or lateral cervical lymph node dissection, the accuracy of [ 18 F]FAA PET/CT were 94.3% (460/488). The SUVmax and TBR of lymph node metastases were significantly higher than normal lymph nodes (mean SUVmax, 8.3±4.6 vs. 2.0±1.5, P <0.0001; mean TBR, 3.6±2.2 vs. 0.9±0.7, P <0.0001).

Conclusions: [ 18 F]FAA PET/CT can be used in the detection of postoperative cervical lymph node metastases in DTC. It may serve as a valuable tool for risk stratification and radioactive iodine treatment decision-making of postoperative DTC.