Numerical Analysis of Sentinel Lymph Node Detection Using Technetium-99m: A Step Toward Objective Scintigraphy Evaluation in Oncology

Objective: Scintigraphy with technetium-99m (Tc-99m) is essential for sentinel lymph node (SLN) detection in gynecological cancers, aiding preoperative planning and reducing unnecessary lymphadenectomy. However, traditional image interpretation is subjective. This study applies numerical tools: signal-to-noise ratio (SNR) and C factor (SLN SNR/ background SNR) to objectively assess scintigraphic image quality and protocol efficacy. Materials and methods: A total of 172 patients with endometrial cancer underwent SLN detection at the Maria Sklodowska-Curie National Research Institute of Oncology, Kraków branch (from 2016–2024). Two protocols were compared: 1. short protocol: 40 MBq Tc-99m, planar imaging - 30 minutes post-injection; 2. long protocol: 120 MBq Tc-99m, planar imaging - 18 hours post-injection. SLN detection was confirmed intraoperatively using a gamma probe and subsequently verified by histopathology. Results: The long protocol achieved a detection sensitivity of 94%, compared to 70% in the short protocol. Based on the analysis, the minimum SNR required for effective SLN detection was 1.46, and the threshold C factor was ≥ 3.61. Although the mean SNR in the long protocol was lower (3.51), the prolonged biological retention of Tc-99m in SLNs contributed to improved detection accuracy. Conclusions: Numerical analysis of SLN scintigraphy in 172 patients provides an objective framework for evaluating image quality and improves detection accuracy. The long protocol offers superior visualization of sentinel lymph nodes. Standardized quantitative imaging may support the development of automated and AI-assisted diagnostic tools in nuclear medicine.