The SENSEI laparoscopic tethered gamma probe for sentinel lymph node biopsy in prostate cancer: initial experience from a multicenter clinical trial

1007 Introduction: Sentinel lymph node biopsy (SLNB) in prostate cancer has the potential to improve the accuracy of staging patients that undergo an extended pelvic lymph node dissection (ePLND). Conventional rigid laparoscopic gamma probes (RLGPs) used for minimally invasive SLNB procedures have limited maneuverability and control which restricts identification of sentinel lymph nodes (SLNs). Tethered laparoscopic gamma probes have been developed by different groups to address these limitations with each probe having different design and performance features [1]. Van Oosterom et al. recently demonstrated improved maneuverability and SLN detection with their DROP-IN probe in a clinical setting [2]. Our group have reported on the successful use of the SENSEI® probe (Lightpoint Medical Ltd.) in a pre-clinical setting [3]. An ongoing prospective, international, multicenter clinical trial evaluates the performance and safety of SENSEI® in patients undergoing 99mTc-nanocolloid SLNB (ClinicalTrials.gov: NCT04632251). Here we present the initial results from the first two cases. Methods: SENSEI® consists of a tethered probe connected to a control unit (Figure 1A). The tethered probe measures 40 mm in length and is compatible with robot-assisted and laparoscopic surgery by fitting through a standard 12 mm laparoscopic port but can also be used for open surgery. The front-facing detector consists of a cesium iodide crystal and a silicon photomultiplier. The grip feature is compatible with standard tissue graspers used for minimally invasive surgery, and the probe can be reoriented in vivo by using either a tissue grasper or needle holder to grasp the side pockets. The control unit provides a numerical and audible read out of the activity levels, and can be connected to an external display (e.g. da Vinci TileProTM). Institutional ethics approval was obtained before patient recruitment commenced in Hospital Del Mar, Barcelona. A transrectal ultrasound-guided 99mTc-nanocolloid injection of 240 ± 10 MBq was given into the peripheral zone of each quadrant of the prostate. Planar lymphoscintigraphy scans (Symbia EvoTM, Siemens) were acquired 30-minutes and 2-hours post-injection. In the morning the next day, a laparoscopic radical prostatectomy was performed followed by SLNB and ePLND. Suspected SLN locations were scanned in vivo with SENSEI® and subsequently with a RLGP (Navigator GPSTM, RMD). All excised SLNs and non-SLNs from the ePLND were measured ex vivo with both probes and all specimens were subsequently sent for post-operative histopathological examination (Figure 1B). Results: 2 SLNs were identified by SENSEI® and the RLGP in each patient (Table 1). In one patient a paraaortic SLN was identified on preoperative imaging but this SLN was not deemed suitable for excision at the time of surgery. SENSEI® recorded a higher count rate than the RLGP in all in vivo and 3/4 ex vivo measurements. All SLN and non-SLNs removed were negative on histopathology. No device-related adverse events occurred. Conclusions: These early results show that SENSEI® can successfully detect SLNs with excellent sensitivity compared to the RLGP and be used in areas outside of the ePLND template (i.e. presacral). Results from further patients including those undergoing robot-assisted and open surgery are awaited to further evaluate the performance and safety of SENSEI® SLNB in a larger patient population. Future applications include 99mTc-PSMA SENSEI® for intraoperative detection of lymph node metastases.