Correlation of tracer uptake in sentinel lymph nodes as measured on SPECT/CT and during intra-operative gamma tracing with SENSEI: the UZ Leuven experience

This retrospective analysis aims to study the relationship between tracer uptake in sentinel lymph nodes (SLNs) as measured on SPECT/CT and during intra-operative gamma tracing with a drop-in gamma probe (SENSEI^®) in patients who participated in the UZ Leuven cohort of a prospective multicentre clinical trial evaluating the SENSEI^® probe for minimally-invasive SLN biopsy (SLNB) in prostate cancer. Correlation of pre- and intraoperative imaging can allow for improved surgical planning, providing important information to guide intraoperative findings.

Nine patients with histologically proven prostate cancer scheduled for radical prostatectomy (RP) with extended pelvic lymph node dissection (ePLND) were prospectively selected for preoperative lymphoscintigraphy with SPECT/CT the day before surgery after intra-prostatic injection of 240 MBq of ^99mTc-nanocolloid under ultrasound guidance. SLNB was performed with the SENSEI^® drop-in gamma probe during standard of care RP with ePLND. SLN detection and counts on SPECT/CT and in vivo and ex vivo probe measurements were compared.

The patient-based detection rate of at least one SLN was 100% on SPECT/CT and 100% intraoperatively with the drop-in gamma probe. In total, 29 SLNs were detected with the probe and 32 SLNs on SPECT/CT. The correlation between SPECT/CT counts and in vivo and ex vivo probe measurements was significant but moderate (Pearson r = 0.57, p = 0.002 and r = 0.64, p = 0.0003, respectively).

Drop-in gamma probe measurements showed a moderate correlation with the SPECT/CT counts. SPECT/CT uptake values can be used as an estimate for in vivo detection of SLNs with the probe.