Detection Rate of 18F-choline-PET/CT and 68Ga-PSMA-HBED-CC-PET/CT for Prostate Cancer Lymph Node Metastases with Direct Link from PET to Histopathology: Dependence on the Size of Tumor Deposits in Lymph Nodes.

Introduction: Accurate detection of prostate cancer lymph node (LN) metastases (LNM) through PET/CT prior to lymphadenectomy (LA) is crucial for successful therapy. PET/CT with choline-derivatives used to be the standard tool for imaging metastases, whereas 68Ga-PSMA-(prostate-specific membrane antigen)-PET/CT was introduced recently. Both PET-techniques were investigated with respect to what extent the detection rate of LNM depends on the size of tumor deposits (TD) within LNM. Methods: Documenting the switch from the use of 18F-choline to 68Ga-PSMA in 2014, we used two patient cohorts undergoing a template LA because of a PET/CT indicating LNM. 44 and 40 patients had PET/CT with 18F-choline or 68Ga-PSMA-ligand. 226 LNM (125 18F-choline, 101 68Ga-PSMA) originated from 73 salvage LAs at biochemical recurrence and from 11 primary LAs at radical prostatectomy. LNM eligible for direct correlation of PET/CT to histopathology were identified from LAs conducted in small anatomical subregions with 1 LNM (condition 1) or 1-2 LNM (condition 2). Longitudinal and short diameter of TD within LNM were determined by histopathology allowing to link the size of TD in LNM to the detection threshold of PET/CT. Diameters associated with a detection rate of 50% and 90% (d50%, d90%) were calculated based on logistic growth curve models fitted. Results: Gleason-score, number of removed LN and subregions for LA per patient did not differ significantly between the 18F-choline-and 68Ga-PSMA-group. Median PSA-level at imaging and number of LNM per patient was significantly higher in the 18F-choline-group (3.4 ng/ml, n = 34) compared to the 68Ga-PSMA-group (2.2 ng/ml, n = 28; both p<0.05). Longitudinal respectively short diameters of TD in LNM to reach d90% was 11.2 mm respectively 7.4 mm for 18F-choline-PET/CT and 6.3 mm respectively 4.9 mm for 68Ga-PSMA-PET/CT. Corresponding diameters to reach d50% were 5.5 mm and 3.3 mm for 18F-choline-PET/CT and 3.7 mm and 2.3 mm for 68Ga-PSMA-PET/CT, respectively. Detection rates were significantly higher under 68Ga-PSMA (P = 0.005 and P = 0.04 for longitudinal and short diameter). Conclusion:68Ga-PSMA-PET/CT is superior in the detection of LNM compared to 18F-choline-PET/CT. Whether those results will lead to an improved patient outcome after 68Ga-PSMA-PET-guided therapy needs to be investigated by further studies.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2019 Jan 25 [Epub ahead of print]

Cordula Annette Jilg, Vanessa Drendel, Hans Christian Rischke, Teresa Isabella Rosa Beck, Kathrin Reichel, Malte Krönig, Ulrich Wetterauer, Wolfgang Schultze-Seemann, Philipp Tobias Meyer, Werner Vach

Department of Urology, Medical Center - University of Freiburg, Faculty of Medicine, Germany., Institute for Pathology, Faculty of Medicine, University of Freiburg, Germany., Department of Radiation Oncology, Medical Center - University of Freiburg, Faculty of Medicine, Germany., Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, Germany., Department of Orthopedics and Traumatology, University Hospital Basel, Switzerland.