Introduction Preoperative imaging combined with intraoperative gamma probe (GP) localization is standard procedure for identifying the sentinel lymph nodes (SLNs) in melanoma patients. The primary aim of this prospective IRB-approved study is to investigate whether an intraoperative portable gamma camera (PGC) improves the intraoperative detection of SLNs when used in conjunction with the GP.
Materials & Methods Planar lymphoscintigraphy and SPECT/CT were performed after injection of a dosage of 600 uCi (1-day protocol) or 2000 uCi (2-day protocol) of [(99m)Tc]Tilmanocept in melanoma patients over 18 years old with a Breslow thickness ≥ 1.0 mm. Preoperatively, the SLNs were localized and the skin overlying the area was marked by the nuclear medicine physician. Intraoperatively, a strict surgical protocol was followed for each identified draining SLN basin. A GP (Neoprobe 2000) was used to locate and remove the SLNs. The resection bed was then explored by the GP using ‘roaming counts’ at 8 positions of the clock and center to make sure that the entire operative field has a negative GP screening (less than 10% of the hottest node). Finally, the PGC (Sentinella S102, Oncovision S.A., Valencia, Spain) was used after a negative GP screening. The Sentinella® PGC was positioned 5 cm above the resection bed with an image acquisition time of 60 seconds. Any depicted radioactive hotspots after a negative GP screening were considered as additional found SLNs by Sentinella® PGC. The hotspots were further explored using the GP to locate and remove additional detected SLNs (applying the >10% rule).
Results First 50 patients (27 males and 23 females) were included in this report. Preoperative imaging localized 70 SLN basins. Intraoperative GP detected 159 SLNs and Sentinella® PGC found additional 60 SLNs, which were removed with the GP guided by the Sentinella images. One palpable lymph node, not detected by GP was positive for micrometastasis. Thus, the identification rate by Sentinella alone was 27% (60/220). Overall, a SLN positive rate of 8.2% (18/220) and a patient positive rate of 26% (13/50) were found. In 32 patients, Sentinella® PGC imaging detected additional SLNs (55 tumor-negative and 5 tumor-positive SLNs) after a negative gamma probe screening. Two of these 5 tumor-positive SLNs being found by Sentinella® PGC prevented a false-negative procedure. Patients will be enrolled to complete the study with a total anticipated number of 100.
Conclusion Interim analysis of this prospective study to date demonstrates that intraoperative PGC imaging provides additional information when standard technique with GP fails. The use of intraoperative imaging has led to the detection of additional SLNs in a significant number of patients. Thus, intraoperative imaging by PGC holds promise for reducing false negative rate for sentinel lymph node biopsy for melanoma.