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 -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_max of lesions on preoperative PSMA PET/CT and their intraoperative counts/s measured using the Drop-In -probe. Methods: A secondary analysis based on the prospective, single-arm, and single-center feasibility study was conducted (NCT03857113). Patients (n = 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 ^99mTc-PSMA-I&S 1 d before surgery. Radioguidance was achieved using a Drop-In -probe. Correlation was determined using the Spearman rank correlation coefficient (s). Subgroup analysis was based on the median SUV_max. Results: In total, 33 lesions were visible on the PSMA PET/CT images, with a median overall SUV_max 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_max (s = 0.728 and 0.763, respectively; P < 0.001). Subgroup analysis based on median SUV_max in the group with an SUV_max of less than 6 showed no statistically significant correlation with the numeric signal in vivo (s = 0.382; P = 0.221) or the signal-to-background-ratio (s = 0.245; P = 0.442), whereas the group with an SUV_max of 6 or more showed respective statistically significant positive correlations (s = 0.774 [P < 0.001] and s = 0.647 [P = 0.007]). Conclusion: Our findings indicate that there is a direct relation between SUV_max on PSMA PET/CT and the readout recorded by the surgical Drop-In probe, thereby indicating that SUV_max 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.

前列腺特异性膜抗原 (PSMA) PET 用于选择复发性前列腺癌患者进行转移导向治疗。手术方法可以通过放射引导手术（RGS）来实现，使用插入式探针来追踪积累放射性信号的病变。为了指导挽救手术的患者选择，我们研究了术前 PSMA PET/CT 上病变的 SUV_最大值与使用 Drop-In 探针测量的术中计数之间的相关性。方法：基于前瞻性、单臂、单中心可行性研究（NCT03857113）进行二次分析。纳入的患者（n = 29）在既往治疗后出现生化复发，且术前 PSMA PET/CT 骨盆内最多有 3 个提示性病变。术前 6 个月内接受雄激素剥夺治疗的患者被排除。所有患者术前1天静脉注射^99m Tc-PSMA-I&S。无线电制导是使用插入式探头实现的。使用斯皮尔曼等级相关系数确定相关性。亚组分析基于 SUV _max中位数。结果： PSMA PET/CT 图像上总共可见 33 个病变，中位总体 SUV_最大值为 6.2（四分位距 [IQR]，4.2-9.7）。 RGS 促进了 31 个病灶的切除。体内 Drop-In 计数/秒中位数为 134（IQR，81-220），离体计数为 109（IQR，72-219）。这些值的强度与 SUV _max相关（s 分别 = 0.728 和 0.763；P < 0.001）。基于 SUV max 小于 6 的组中 SUV max 中位数的亚组分析_显示，_与体内数字信号 (s = 0.382；P = 0.221) 或信号背景比 (s = 0.245；P = 0.442），而 SUV _max为 6 或以上的组分别显示出统计学上显着的正相关性（s = 0.774 [ P < 0.001] 和 s = 0.647 [ P = 0.007]）。结论：我们的研究结果表明，PSMA PET/CT 上的 SUV _max与手术 Drop-In 探针记录的读数之间存在直接关系，从而表明 SUV _max可用于选择 PSMA RGS 患者。对于治疗建议的更明确的亚组定义，需要进一步的研究来验证目前的发现。