BackgroundLymph 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)-99mTc-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-99mTc-nanoscan compared to ICG-99mTc-nanocolloid from a nuclear and surgical perspective.MethodsTwenty-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-99mTc-nanocolloid until no longer available; the second group (n= 13) received ICG-99mTc-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.ResultsThe mean tracer uptake in the SNs was similar for ICG-99mTc-nanocolloid (2.2 ± 4.3%ID) and ICG-99mTc-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-99mTc-nanoscan compared to 2 SNs (IQR 2–3) in PeCa patients receiving ICG-99mTc-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-99mTc-nanoscan group (24*109arbitrary units (A.U) IQR 1.6*109–14*109in the ICG-99mTc-nanocolloid group versus 4.6*109A.U. IQR 2.4*109–42*109in the ICG-99mTc-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.ConclusionsBased on this retrospective analysis, we can conclude that ICG-99mTc-nanoscan has similar capacity for SN identification as ICG-99mTc-nanocolloid and can safely be implemented in SN procedures.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00259-023-06157-9.