Abstract
PurposeIntraoperative identification of prostate cancer (PCa) lymph node (LN) metastases (LNM) detected by preoperative PSMA PET/CT may be facilitated by PSMA radio-guided surgery (RGS) with use of a γ-probe. Earlier we demonstrated excellent performance of the 111In-labelled PSMA ligand DKFZ-617 ([111In]In-PSMA-617) in RGS for ex situ distinction of LN vs LNM at lymphadenectomy (LA) at a single LN level. In comparison with indium-111, technetium-99m has better physical properties for γ-probe measurements, better availability and lower radiation exposure for patients and medical personnel. Against this background, we evaluated the uptake of 99mTc-PSMA-I&S ligand at the level of single LN and its power to discriminate between unaffected LN and LNM.MethodsSix patients with PCa with the suspicion of LNM on preoperative PSMA-PET/CT underwent [99mTc]Tc-PSMA-I&S RGS (4 salvage LA, 2 primary LA) with intravenous injection of [99mTc]Tc-PSMA-I&S 24 h prior to surgery. Resected samples were isolated manually aiming at the level of single LN. Uptake measurements were done ex situ with a high-purity germanium detector. Receiver operating characteristic (ROC) analysis was performed based on [99mTc]Tc-PSMA-I&S uptake expressed as lean body mass standard uptake value (SUL).ResultsSeparation of the tissue samples from 73 subregions resulted in 498 single samples. After final histopathology 356 LN, 160 LNM und 11 non-nodal PCa samples were identified. Median SUL of tumor-free samples (0.26) and samples with cancer (3.5) was significantly different (p < 0.0001). ROC analysis revealed an area under the curve (AUC) of 0.917 (95% CI 0.89–0.95). Using a SUL cutoff of 1.1, sensitivity, specificity, positive predictive value, and negative predictive values were 76.6%, 94.4%, 89.4% and 86.9%.ConclusionEx situ analysis of [99mTc]Tc-PSMA-I&S uptake at single LN level showed good diagnostic performance for the ex situ distinction of tumor-bearing vs tumor-free LN during RGS.
Highlights
Prostate cancer (PCa) is the most commonly diagnosed cancer in men [1, 2]
Receiver operating characteristic (ROC) analysis was performed based on [99mTc]Tc-prostate-specific membrane antigen (PSMA)-I&S uptake expressed as lean body mass standard uptake value (SUL)
receiver operating characteristic (ROC) analysis revealed an area under the curve (AUC) of 0.917
Summary
Prostate cancer (PCa) is the most commonly diagnosed cancer in men [1, 2]. Pelvic and retroperitoneal lymph nodes (LN) are the first site for metastases [2, 3]. About 15–30% of the patients will develop a biochemical recurrence with elevated PSA level and clinical recurrence (metastases) possible at different anatomical sites [5, 6]. PET/CT targeting prostate-specific membrane antigen (PSMA) using 68Ga-labelled PSMA ligands has demonstrated an excellent ability to detect LNM prior to surgery and is widely used as a tool for staging before primary therapy and for restaging in the setting of biochemical relapse [7, 9,10,11]. Due to several advantages of the positron emitter fluorine-18, more and more frequently 18F-labelled PSMA ligands ([18F] F-PSMA-1007, [18F]F-DCFPyL) are used for PET/CT imaging [12,13,14,15]
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