Double-phase I-131 whole body scan and I-131 SPECT-CT images in patients with differentiated thyroid cancer: Effectiveness for accurate identification

Objectives This study aimed at determining whether I-131 double-phase whole body scan (WBS) and SPECT-CT images at their first radioactive iodine (RAI) treatment have an additional value over single-phase WBS image in identifying benign and malignant lesions in patients with well-differentiated thyroid cancer (DTC).

Methods This study included 42 DTC patients who were treated for their first radioablation. Post-therapeutic WBS images were acquired after 3 days (early phase) and 7 days (delayed phase). Following early-phase WBS, the SPECT-CT image was obtained. The images were reviewed independently of the clinical data by 2 board-certified observers with a 6-point scoring system (benign to malignant -3 to +3).

Results The double-phase WBS and SPECT-CT images showed 115 radioiodine-avid localizations (81 benign and 34 malignant accumulations). Confidence levels of benign accumulations were significantly higher with SPECT-CT (average score; -2.40±1.06) compared to the early-phase WBS images (average score; -1.39±1.88) (Wilcoxon test: z=-6.80, p<.0001). When the analysis was restricted to accumulations with low confidence score in the early-phase WBS image, the delayed-phase WBS image was useful for 23 lesions (51%). The confidence levels of malignant accumulations were significantly higher with SPECT-CT images (average score; 2.35±0.96) compared to the early-phase WBS image (average score; 1.42±1.22) (z=3.51, p=0.0005).

Conclusions Post-therapeutic SPECT-CT image was superior to the early-phase WBS image for lesion detectability and accurate identification of anatomical localization. The delayed-phase WBS image assisted accurate diagnosis about benign lesions with a low confidence level in the early-phase WBS image