Comparison of two hybrid sentinel node tracers: indocyanine green (ICG)-(99m)Tc-nanocolloid vs. ICG-(99m)Tc-nanoscan from a nuclear medicine and surgical perspective

BACKGROUND: Lymph node (LN) metastasis is a relevant predictor for survival in patients with a.o. penile cancer (PeCa), malignant melanoma. The sentinel node (SN) procedure comprises targeted resection of the first tumour-draining SNs. Here, the hybrid tracer indocyanine green (ICG)-(99m)Tc-nanocolloid has been used for several years to combine optical and nuclear detection. Recently, the resource of the nanocolloid precursor stopped production and the precursor was replaced by a different but chemically comparable colloid, nanoscan. Our aim was to study the performance of ICG-(99m)Tc-nanoscan compared to ICG-(99m)Tc-nanocolloid from a nuclear and surgical perspective. METHODS: Twenty-four patients with either PeCa or head-and-neck (H&N) melanoma and scheduled for a SN procedure were included. The initial group (n = 11) received ICG-(99m)Tc-nanocolloid until no longer available; the second group (n = 13) received ICG-(99m)Tc-nanoscan. Tracer uptake was assessed on lymphoscintigraphy and single-photon emission (SPECT). Intraoperatively, SNs were identified using gamma tracing and fluorescence imaging. Ex vivo (back-table) measurements were conducted to quantify the fluorescence emissions. Chemical analysis was performed to compare the ICG assembly on both precursors. RESULTS: The mean tracer uptake in the SNs was similar for ICG-(99m)Tc-nanocolloid (2.2 ± 4.3%ID) and ICG-(99m)Tc-nanoscan (1.8 ± 2.6%ID; p = 0.68). 3 SNs (interquartile range (IQR) 3–4) were detected on lymphoscintigraphy in PeCa patients receiving ICG-(99m)Tc-nanoscan compared to 2 SNs (IQR 2–3) in PeCa patients receiving ICG-(99m)Tc-nanocolloid (p = 0.045), no differences were observed in H&N patients. Back-table measurements of resected SNs revealed a lower total fluorescence intensity in the ICG-(99m)Tc-nanoscan group (24*10(9) arbitrary units (A.U) IQR 1.6*10(9)–14*10(9) in the ICG-(99m)Tc-nanocolloid group versus 4.6*10(9) A.U. IQR 2.4*10(9)–42*10(9) in the ICG-(99m)Tc-nanoscan group, p = 0.0054). This was consistent with a larger degree of “stacked” ICG observed in the nanoscan formulation. No tracer-related adverse events were reported. CONCLUSIONS: Based on this retrospective analysis, we can conclude that ICG-(99m)Tc-nanoscan has similar capacity for SN identification as ICG-(99m)Tc-nanocolloid and can safely be implemented in SN procedures. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00259-023-06157-9.