Intraoperative laparoscopic fluorescence guidance to the sentinel lymph node in prostate cancer patients: clinical proof of concept of an integrated functional imaging approach using a multimodal tracer

Background: Integration of molecular imaging and in particular intraoperative image guidance is expected to improve the surgical accuracy of laparoscopic lymph node (LN) dissection.

Objective: To show the applicability of combining preoperative, intraoperative, and postoperative sentinel node imaging using an integrated diagnostic approach based on an imaging agent that is both radioactive and fluorescent.

Design, setting, and participants: Before surgery, multimodal indocyanine green (ICG)-(99m)Tc-NanoColl was injected into the prostate. Subsequent lymphoscintigraphy and single-photon emission computed tomography/computed tomography (SPECT/CT) imaging of pelvic nodes was performed to determine the location of the sentinel lymph nodes (SLNs) preoperatively. During the surgical procedure a fluorescence laparoscope, optimized for detection in the near infrared range, was used to visualize the nodes identified on SPECT/CT. Eleven patients scheduled for robot-assisted laparoscopic prostatectomy (RALP) with an increased risk of nodal metastasis, based on Memorial Sloan-Kettering Cancer Center/Kattan nomogram estimation, participated in a pilot assessment (N09IGF).

Surgical procedure: Patients underwent RALP with LN dissection for prostate cancer.

Measurements: Radioactive and fluorescent signals were monitored using different modalities, and the correlation between the two types of signals was studied. The location of preoperatively detected SLNs was documented.

Results and limitations: Preoperatively, SLNs were identified by SPECT/CT, and the multimodal nature of the imaging agent also enabled intraoperative detection via fluorescence imaging. Fluorescence particularly improved surgical guidance in areas with a high radioactive background signal such as the injection site. Ex vivo analysis revealed a strong correlation between the radioactive and fluorescent content in the excised LNs. Fluorescence detection is limited by the severe tissue attenuation of the signal. Therefore, radio guidance to the areas of interest is still desirable.

Conclusions: Initial data indicate that multimodal ICG-(99m)Tc-NanoColloid, in combination with a laparoscopic fluorescence laparoscope, can be used to facilitate and optimize dissection of SLNs during RALP procedures.