Is there an additional benefit of Tc-99m-PSMA-guided gamma probe use for salvage lymph node dissection in recurrent prostate cancer.

Abstract

e591 Background: PSMA-PET/CT is the most sensitive diagnostic tool in biochemical recurrent prostate cancer to detect minimal metastatic disease. However, it may be difficult to localize small PSMA-positive lymph nodes intraoperatively. Therefore, it was the aim to investigate whether preoperative Tc-99m-PSMA targeting may improve intraoperative tumor localization by use of a gamma probe. Methods: In 13 Patients Ga-68-PSMA-PET/CT identified iliac lymph nodes in patients suitable for salvage lymph node dissection. On the day before operation a mean activity of 480 MBq Tc-99m-PSMA was injected and gamma camera scintigraphy + SPECT was performed 4-5 hours after tracer application. About 24 hours after tracer application a salvage lymph node dissection was performed on the side of initial suspicious lymph node metastases. Sensitivity, specifity, pos and neg. predictive values were calulated for PSMA-PET/CT and gamma probe use to analyse the additional use. Results: In 9 / 13 patients PSMA-positive metastatic lymph nodes were identified in Ga-68 PSMA-PET/CT. A total of 156 lymph nodes were removed with 14 lymph nodes in 9 patients being positive in histopathologic examination. Sensitivity, specifity, pos and neg. predictive values for PSMA PET/CT and gamma probe were 85% and 79%, 99% and 100%, 85% and 100% and 99% and 98% respectively. In one patient only gamma probe use identified a pathologic lymph node. Conclusions: Gamma probe guided salvage lymph node dissection in PSA recurrent prostate cancer is feasible and had a high concordance with PSMA-PET/CT. However, the additional diagnostic benefit is limited compared to PSMA-PET/CT because in only one patient (7%) a positive lymph node could be identified with the use of the gamma probe outside the standard operative area in salvage lymph node dissection.