Intraoperative Imaging with a Portable Gamma Camera May Reduce the False-Negative Rate for Melanoma Sentinel Lymph Node Surgery

BACKGROUND: Preoperative imaging and intraoperative gamma probe (GP) localization is standard for identifying sentinel lymph nodes (SLNs) in melanoma patients. The aim of this prospective Institutional Review Board-approved study was to investigate whether an intraoperative portable gamma camera (PGC) improves SLN detection over the GP. METHODS: Lymphoscintigraphy and single photon emission computed tomography/computed tomography were performed after injection of 99mTc-Tilmanocept in melanoma patients (≥ 18 years, Breslow thickness ≥ 1.0 mm). A GP was used to localize the SLNs in each basin, which was explored by the GP to ensure that the operative field was < 10% counts of the hottest SLN. The PGC was then used after a negative GP screening. Any residual hotspots identified by the PGC were considered as additional SLNs and were removed following the 10% rule. RESULTS: Preoperative imaging of 100 patients identified 138 SLN basins, with 306 SLNs being identified by conventional surgery. The PGC localized 89 additional SLNs in 54 patients. Thus, the PGC identified an additional 23% of SLNs [95% confidence interval (CI) 18–27%]. Four of these 89 SLNs showed micrometastasis in four patients, in two of whom the only tumor-positive SLN was identified by the PGC, preventing two false-negative cases. Thus, the null hypothesis that the PGC did not detect additional positive SLNs was rejected (p = 0.000). The overall SLN positive rate was 9.9% (39/395, 95% CI 6–12), and the overall patient positive rate was increased using the PGC, from 25 to 27% (27/100). CONCLUSIONS: Intraoperative PGC imaging yielded additional SLNs in a significant number of patients over GP alone. Identification of these additional SLNs resulted in upstaging of four patients with two patients being converted from a negative to a positive status, thus, preventing two false-negative cases.