Feasibility of different lymph node metastases delineation approaches in [18F]SiTATE PET/CT imaging in NET patients

Siegmund, Sophie Carina; Schöll, Magdalena; Wenter, Vera U.; Sheikh, Gabriel T.; Scheifele, Maximilian; Gildehaus, Franz Josef; Lindner, Simon; Sundar, Lalith K. Shiyam; Spitzweg, Christine ; Auernhammer, Christoph J.; Werner, Rudolf A.; Zacherl, Mathias J. (2025): Feasibility of different lymph node metastases delineation approaches in [18F]SiTATE PET/CT imaging in NET patients. EJNMMI Reports, 9: 37. ISSN 3005-074X

Abstract

Background

Accurate tumor delineation in somatostatin receptor (SSTR) PET/CT is imperative for quantifying tumor burden, therapy monitoring, and response assessment in gastroenteropancreatic neuroendocrine tumors (GEPNETs). This study aimed to evaluate different SSTR PET-based tumor delineation approaches, based on a lymph node metastasis as reference standard, and determine the most robust method for volume assessment. Singular, non-bulky lymph node metastases with a short axis diameter ≥ 1.0 cm from [¹⁸F]SiTATE PET/CT scans were included. Different tumor delineation methods were applied: fixed SUV thresholds, isocontours relative to SUV max , and individual backwards thresholding. The correlation between PET-derived volumes and CT-derived volumes (reference standard) were investigated.

Results

An isocontour approach using 45% of SUV max demonstrated the strongest correlation with CT-derived volumes ( r = 0.874; r² = 0.764; p < 0.001), outperforming fixed SUV thresholds, e.g. SUV 4.0 ( r = 0.727; r 2 = 0.529; p < 0.001). The application of a backwards threshold approach resulted in the identification of significant variability (CoV: 59.6% for fixed SUV, 31.3% for isocontour).

Conclusion

The 45% isocontour-thresholding relative to lesional SUV max approach constitutes a robust and clinically applicable method for SSTR PET-based tumor delineation in GEPNET patients, irrespective of changes of SSTR avidity of reference tissues (e.g. liver). Further validation is required to establish its role in total tumor volume assessment and therapy monitoring.

• Doc-Type: Article (LMU Hospital)
• Organisational unit (Faculties): 07 Medicine > Medical Center of the University of Munich > Medical Clinic and Outpatient Clinic IV (Endocrinology, nephrology, other sections); 07 Medicine > Medical Center of the University of Munich > Clinic and Polyclinic for Nuclear Medicine; 07 Medicine > Medical Center of the University of Munich > Clinic and Polyclinic for Radiology
• DFG subject classification of scientific disciplines: Life sciences
• DFG: Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - 491502892