Feasibility and Optimal Dosage of Indocyanine Green Fluorescence for Sentinel Lymph Node Detection Using Robotic Single-Site Instrumentation: Preclinical Study

The present study was performed to determine the optimal dosage of indocyanine green (ICG) to accurately differentiate the sentinel node from surrounding tissue and then to test this dosage using novel single-port robotic instrumentation. The study was performed in healthy female pigs. After induction of anesthesia, all pigs underwent exploratory laparotomy, dissection of the bladder, and colpotomy to reveal the cervical os. With use of a 21-gauge needle, 0.5 mL normal saline solution was injected at the 3- and 9-o'clock positions as control. Four concentrations of ICG were constituted for doses of 1000, 500, 250, and 175 μg per 0.5 mL. ICG was then injected at the 3- and 9-o'clock positions on the cervix. The SPY camera was used to track ICG into the sentinel nodes and to quantify the intensity of light emitted. SPY technology uses an intensity scale of 1 to 256; this scale was used to determine the difference in intensity between the sentinel node and surrounding tissues. The optimal dosage was tested using single-port robotic instrumentation with the same injection techniques. A sentinel node was identified at all doses except 175 μg, at which ICG stayed in the cervix and vasculature only. For both the 500- and 250-μg doses, the sentinel node was identified before reaching maximum intensity. At maximum intensity, the difference between the surrounding tissue and the node was 207 (251 vs 44) for the 500-μg dose and 159 (251 vs 92) for the 250-μg dose. Sentinel lymph node (SLN) biopsy was successfully performed using single-port robotic technology with both the 250- and 500-μg doses. For SLN detection, the dose of ICG is related to the ability to differentiate the sentinel node from the surrounding tissue. An ICG dose of 250 to 500 μg enables identification of a SLN with more distinction from the surrounding tissues, and this procedure is feasible using single-port robotics instrumentation.