Strong Correlation Between SUV on PSMA PET/CT and Numeric Drop-In γ-Probe Signal for Intraoperative Identification of Prostate Cancer Lesions.

Prostate-specific membrane antigen (PSMA) PET is used to select patients with recurrent prostate cancer for metastasis-directed therapy. A surgical approach can be achieved through radioguided surgery (RGS), using a Drop-In γ-probe that traces lesions that accumulate the radioactive signal. With the aim of guiding patient selection for salvage surgery, we studied the correlation between the SUV of lesions on preoperative PSMA PET/CT and their intraoperative counts/s measured using the Drop-In γ-probe. A secondary analysis based on the prospective, single-arm, and single-center feasibility study was conducted (NCT03857113). Patients ( = 29) with biochemical recurrence after previous curative-intent therapy and a maximum of 3 suggestive lesions within the pelvis on preoperative PSMA PET/CT were included. Patients treated with androgen deprivation therapy within 6 mo before surgery were excluded. All patients received an intravenous injection of Tc-PSMA-I&S 1 d before surgery. Radioguidance was achieved using a Drop-In γ-probe. Correlation was determined using the Spearman rank correlation coefficient (ρs). Subgroup analysis was based on the median SUV In total, 33 lesions were visible on the PSMA PET/CT images, with a median overall SUV of 6.2 (interquartile range [IQR], 4.2-9.7). RGS facilitated removal of 31 lesions. The median Drop-In counts/s were 134 (IQR, 81-220) in vivo and 109 (IQR, 72-219) ex vivo. The intensity of the values correlated with SUV (ρs = 0.728 and 0.763, respectively; < 0.001). Subgroup analysis based on median SUV in the group with an SUV of less than 6 showed no statistically significant correlation with the numeric signal in vivo (ρs = 0.382; = 0.221) or the signal-to-background-ratio (ρs = 0.245; = 0.442), whereas the group with an SUV of 6 or more showed respective statistically significant positive correlations (ρs = 0.774 [ < 0.001] and ρs = 0.647 [ = 0.007]). Our findings indicate that there is a direct relation between SUV on PSMA PET/CT and the readout recorded by the surgical Drop-In probe, thereby indicating that SUV can be used to select patients for PSMA RGS. For more definitive subgroup definitions for treatment recommendations, further studies are necessary to validate the present findings.