Comparing the hybrid fluorescent-radioactive tracer indocyanine green-99mTc-nanocolloid with 99mTc-nanocolloid for sentinel node identification: a validation study using lymphoscintigraphy and SPECT/CT

Abstract

The purpose of this study was to compare the lymphoscintigraphic drainage patterns of a hybrid sentinel node tracer consisting of the fluorescent dye indocyanine green (ICG) and (99m)Tc-nanocolloid with the drainage pattern of (99m)Tc-nanocolloid alone, the current standard tracer in many European countries.

Methods: Twenty-five patients with a melanoma in the head and neck region (n = 10), a melanoma on the trunk (n = 6), or penile carcinoma (n = 9) who were scheduled for sentinel node biopsy were prospectively included. First, the standard (99m)Tc-nanocolloid procedure was performed. After injection at the lesion site, lymphoscintigraphy was performed with a 10-min dynamic study and static planar images at 10 min and 2 h after injection, followed by SPECT/CT. The same scintigraphic procedure was repeated after injection of hybrid ICG-(99m)Tc-nanocolloid the same afternoon in 10 patients or the next morning in 15 patients. The paired images of both injections were evaluated, and count rates in the sentinel nodes were calculated and compared. Sentinel nodes were surgically localized using blue dye, a γ-ray detection probe, a portable γ-camera, and a fluorescence camera.

Results: Lymphatic drainage was visualized in all 25 patients using (99m)Tc-nanocolloid, leading to the identification of 66 sentinel nodes in total. These same sentinel nodes were also identified during the second scintigraphic procedure with ICG-(99m)Tc-nanocolloid. Moreover, a high correlation between the radioactive counting rates in the sentinel nodes of both scintigraphic studies was observed (mean R(2) = 0.83). Intraoperatively (4-23 h after the second injection), all preoperatively identified sentinel nodes could be localized using radio- and fluorescence guidance combined. In total, 95% of the sentinel nodes could be intraoperatively visualized by means of fluorescence imaging, whereas merely 54% stained blue. Ex vivo, all radioactive sentinel nodes were fluorescent and vice versa. No adverse reactions were observed.

Conclusion: The lymphatic drainage pattern of ICG-(99m)Tc-nanocolloid is identical to that of (99m)Tc-nanocolloid. This observation, together with the added value of intraoperative fluorescence guidance, warrants wider evaluation of hybrid ICG-(99m)Tc-nanocolloid as a tracer for sentinel node procedures.