Optimal Time for 124I PET/CT Imaging in Metastatic Differentiated Thyroid Cancer

Area of Science:

• Nuclear Medicine
• Radiology
• Oncology

Background:

• Differentiated thyroid cancer (DTC) often metastasizes, necessitating sensitive imaging techniques.
• 124I PET/CT is a valuable tool for detecting locoregional and distant metastases in DTC.
• Determining the optimal imaging time is crucial for maximizing diagnostic accuracy.

Purpose of the Study:

• To determine the optimal timing for 124I PET/CT imaging in patients with differentiated thyroid cancer.
• To maximize the detection rate of locoregional and distant metastases.
• To compare the efficacy of single versus dual-time-point imaging.

Main Methods:

• Patients with suspected metastatic DTC underwent 124I PET/CT over 4 days after radioiodine administration.
• Scans were analyzed visually and quantitatively, assessing lesion uptake intensity and volume.
• Comparison of lesion detection rates and quantitative metrics across different time points (2, 24, 48, 72, 96 hours).

Main Results:

• The 48-hour scan showed the highest detection rate for distant metastases.
• Dual-time-point imaging (48+72h or 48+96h) yielded the highest overall lesion detection rate.
• Quantitative analysis revealed peak uptake and lesion-to-background ratios at different time points, with lung metastases showing highest ratios at 72 and 96 hours.

Conclusions:

• Dual-time-point 124I PET/CT imaging is superior to single-time-point imaging for detecting DTC metastases.
• Optimal visual detection is achieved with dual time points at 48 + 72 hours or 48 + 96 hours.
• For suspected lung metastases or negative initial scans, delayed imaging at 72 or 96 hours is recommended.