18-Hour Planar Scintigraphy Versus SPECT/CT for Sentinel Lymph Node Detection in Early-Stage Endometrial Cancer

Background: /Objectives: Preoperative detection of sentinel lymph nodes (SLN) using technetium-99m (Tc-99m) is crucial for surgical staging in early-stage endometrial cancer (EC). The optimal imaging timing and modality remain debated. This study compares early planar scintigraphy (30 min), SPECT/CT (1 h), and 18-hour planar scintigraphy after a single Tc-99m injection. Methods: A total of 125 patients with early-stage EC underwent SLN mapping with Tc-99m (120 MBq). Imaging included 30-minute planar scintigraphy, SPECT/CT (1h), and 18-hour planar scintigraphy on the day of surgery. Detection sensitivity, bilateral mapping rate, and image quality (signal-to-noise ratio [SNR], contrast factor [C-factor]) were evaluated, with intraoperative gamma probe detection and histopathology as references. Results: The 18-hour planar scintigraphy achieved the highest SLN detection sensitivity (94,40%, 118/125) compared to SPECT/CT (87,20%, OR=2,48, 95% CI: 0,98–6,27, p=0,051) and 30-minute scintigraphy (72,00%). Bilateral detection was higher at 18 h (80,80%) than SPECT/CT (73,60%). All SLNs detected at 18 h were confirmed intraoperatively and histo-logically, yielding 100% PPV (95% CI: 96,9–100,0%) and NPV (95% CI: 59,0–100,0%). The 18-h protocol showed superior imaging contrast (C-factor: 10,30 ± 1,22) despite lower re-sidual activity. The method remained effective in patients with BMI ≥30 (94,00%). Only 1,60% of patients required hysterectomy before mapping due to background interference. Conclusions: The 18-hour planar scintigraphy is a highly effective, low-cost, and accessi-ble method for SLN detection in early-stage EC, potentially reducing the need for SPECT/CT, radiation exposure, and costs.