Feasibility of different tumor delineation approaches for 18F-PSMA-1007 PET/CT imaging in patients with metastatic prostate cancer

Ziel/Aim Thresholds for total tumor delineation using ¹⁸F-PSMA-1007 PET are not yet established. As correlation of PET-based information and morphological extent in osseous and visceral metastases is hampered by morphological delineation, low contrast in liver tissue and movement artefacts, we correlated CT-based volume of large lymph node metastases (LNM) and PET-based delineation approaches for optimal PET-thresholding.

Methodik/Methods Fifty patients with metastatic prostate cancer, ¹⁸F-PSMA-1007 PET/CT and non-bulky LNM (short-axis diameter ≥10mm) were included. 50 LNM were volumetrically assessed on contrast-enhanced CT (volumetric reference standard). Different approaches for tumor volume delineation were applied and correlated with the reference standard: I) fixed SUV threshold, II) isocontour thresholding relative to SUV_max (SUV%), thresholds relative to III) liver (SUV_liver), IV) parotis (SUV_parotis) and V) spleen (SUV_spleen).

Ergebnisse/Results A fixed SUV of 4.0 (r = 0.807, r²=0.651, p < 0.001) showed the best overall association. 55 % SUV_max (r = 0.627, r²=0.393, p < 0.001) showed highest association using an isocontour. Best background-based approaches were 60 % SUV_liver (r = 0.715, r²=0.511, p < 0.001), 80 % SUV_parotis (r = 0.762, r²=0.581, p < 0.001) and 60 % SUV_spleen (r = 0.645, r²=0.416, p < 0.001). Background tissues SUV_liver, SUV_parotis & SUV_spleen were not correlated (p > 0.05 each). Recently reported cut-offs for intraprostatic tumor delineation (isocontour 44 % SUV_max) revealed inferior association for LNM delineation (r = 0.552, r²=0.305, p < 0.001). Feasibility for total tumor volume delineation was confirmed in the cohort subsequently.

Schlussfolgerungen/Conclusions A simple threshold of SUV 4.0 for delineation showed the highest association with the volumetric reference standard independent of potential changes of PSMA-avidity in background tissues (e. g. parotis). This approach is easily applicable in clinical routine without specific software requirements. Further studies applying this approach for total tumor volume delineation are underway.

Publication History

Article published online:
08 April 2021