Robotic-assisted fluorescence sentinel lymph node mapping using multimodal image guidance in an animal model

Objective: To investigate positron emission tomography/computed tomography (PET/CT) preoperative imaging and intraoperative detection of a fluorescent-labeled receptor-targeted radiopharmaceutical in a prostate cancer animal model.

Materials and methods: Three male beagle dogs underwent an intraprostatic injection of fluorescent-tagged tilmanocept, radiolabeled with both gallium Ga-68 and technetium Tc-99m. One hour after injection, a pelvic PET/CT scan was performed for preoperative sentinel lymph node (SLN) mapping. The definition of SLN was a standardized uptake value that exceeded 5% of the lymph node with the highest standardized uptake value. Thirty-six hours later, we performed robotic-assisted SLN dissection using a fluorescence-capable camera system. Fluorescent lymph nodes were clipped, the abdomen was opened, and the pelvic and retroperitoneal nodes were excised. All excised nodal packets were assayed by in vitro nuclear counting and reported as the percentage of injected dose.

Results: Preoperative PET/CT imaging identified a median of 3 SLNs per animal. All SLNs (100%) identified by the PET/CT were fluorescent during robotic-assisted lymph node dissection. Of all fluorescent nodes visualized by the camera system, 9 of 12 nodes (75%) satisfied the 5% rule defined by the PET/CT scan. The 2 lymph nodes that did not qualify accumulated <0.002% of the injected dose.

Conclusion: Fluorescent-labeled tilmanocept has optimal logistic properties to obtain preoperative PET/CT and subsequent real-time intraoperative confirmation during robotic-assisted SLN dissection.