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.