Optimal Efficient Imaging Time for Identification of Sentinel Lymph Node with Technetium (99mTc) Tilmanocept in Breast Cancer Patients

Background: Pre-operative lymphatic mapping with 99mTc-radiopharmaceuticals are used with a hand-held intraoperative gamma counter to assist in the localization of sentinel lymph node (SLN) in breast cancer patients. Technetium (99mTc) Tilmanocept is a high specificity injectable receptor-binding radiopharmaceutical agent for SLN localization and lymphatic mapping via multiple injections technique and imaging times. Objectives: The primary objective was to evaluate the efficiency of 99mTc Tilmanocept in the visualization of lymph nodes (LN) in breast cancer patients using different imaging times to identify the sentinel lymph node (SLN) in the operating room. Furthermore, optimal imaging time would provide an efficient approach for subsequent same day surgical SLN resection without further delay in pathology results. Methods: We performed a retrospective analysis in 651 patients that underwent lymphaticmapping by comparing imaging time after full or partial intradermal injection technique of 99mTc Tilmanocep in the affected breast. Patients imaging were classified according to time performed either immediately, at 15 minutes or 90 minutes post-tracer administration. Distributions were examined for the binary variable coding ≥1 LN identification vs none across scan time approaches. Statistical differences in LN identification between patients undergoing both immediate and 90 minutes imaging were assessed using McNemar's test. Additionally, the kappa coefficient was examined to assess agreement between immediate vs 90 minute imaging. LN identification in the population of patients with 90 minute (n=203) was compared to another population with 15 minute imaging (n=145) using Pearson Chi-square testing. Results: Of the 651 total patients in the study population, 506 patients had immediate imaging scans. Of these 506 patients, 203 (40.1%) also had a 90 minutes imaging. Of the 203 patients with both immediate and 90 minutes imaging, 54 (26.6%) had 1+ lymph nodes identified with immediate imaging and 196 (96.6%) had 1+ lymph nodes identified at 90 minutes. Differences between immediate and 90 minutes delayed imaging indicate higher identification of lymph nodes at 90 minutes (p