MP57-01 THE DIAGNOSTIC ACCURACY OF 68GA-PSMA-PET/CT FOR DETECTION OF LYMPH NODE METASTASES IN THE SETTING OF SALVAGE LYMPH NODE DISSECTION

INTRODUCTION AND OBJECTIVES: Accurate imaging of lymph node metastases (LNM) is a prerequisite for metastases directed therapies such as salvage lymph node dissection (salvage-LND) in nodal recurrent prostate cancer (PCa). Our aim was to evaluate the diagnostic accuracy of 68PSMA-PET/CT (DKFZ-11) for nodal relapse of PCa according to different topographical locations and the size of tumor deposits in lymph nodes (LN). METHODS: 25 patients with the suspicion of nodal PCa-relapse after primary therapy underwent pelvic and/or retroperitoneal salvage-LND after a whole body PET/CT with 68Ga-PSMA showing PET-positive lesions. Time from PET/CT to salvage-LND was median 2.3 months. Diagnostic accuracy of PET/CT for dissected main-regions (pelvic left/right, retroperitoneal) and subregions (common, external, internal iliac, obturatoria, presacral, aortic-bifurcation, aortal, caval, interaortocaval) was determined by comparing histopathologic results with PET/CT-findings. Size ofmetastatic infiltration inLNwasmeasuredbasedonhistopathology. RESULTS: Mean PSA at salvage-LND was 3.03 ng/ml (SD 3.2 / median 1.74 ng/ml). Overall, 833 LN were resected in 25 patients, containing 98 LNM, corresponding to a mean of 33.3 LN and 3.9 LNM per patient. In 5 patients (8 subregions) tissue containing solid non-nodal local relapse was additionally resected. LN were removed in portions out of 10 subregions per patient leading to 251 subregions available for evaluation. Median 3 LN were removed per subregion. For 2/25 patients and in 7/251 subregions, the suspected tumor involvement was verified by follow-up PET/CT showing progress of the lesions and PSA increase. 35/60 (58.3%) of the main regions and 63/251 (25%) of the subregions were PET-positive. Sensitivity, specifity, positive predictive value (PPV), negative predictive value (NPV) and accuracy based on a main-region analysis was 92.1% (35/38), 100% (22/22), 100% (35/35), 88.0% (22/25) and 95.0% (57/60). Based on a subregion-analyses sensitivity, specifity, PPV, NPV and accuracy was 80.7 % (63/78), 100% (173/173), 100% (63/63), 92.0% (173/188) and 94.0% (236/251). Median diameter (6 mm) of tumor deposits in LNM removed from true-positive subregions was significantly different to LNM resected from false-negative subregions (2 mm) (p<0.0001). CONCLUSIONS: 68PSMA-PET/CT shows high diagnostic accuracy for detection of LNMand served therefore as an essential guidance for salvage-LND. LNM removed from false-negative subregions were significantly smaller compared to LNM removed from true-positive subregions.