Dose optimization of second window indocyanine green in meningioma patients

Surgery remains the first line treatment for meningiomas and can benefit from fluorescence-guided surgical techniques such as second-window indocyanine green (SWIG). In the current study, we compared the use of the standard SWIG dose of 5.0 mg/kg relative to 2.5 mg/kg indocyanine green (ICG) in meningioma patients.

Patients were prospectively enrolled in an IRB-approved study of SWIG and received either the standard dose of 5.0 mg/kg or a reduced dose of 2.5 mg/kg of ICG around 24 h prior to their surgery. Intraoperative near-infrared fluorescence imaging was performed with exo- and endoscopic systems. Signal-to-background ratio (SBR) was calculated to quantify fluorescence and was compared between 5.0 mg/kg and 2.5 mg/kg ICG. All patients received pre-operative MRI and, in select cases, the pre-operative MRI was correlated to intraoperative fluorescence imaging.

In the current study, we found no significant difference in the SBR of meningiomas in patients that were administered with either 5.0 mg/kg or 2.5 mg/kg ICG. However, in five patients that received the standard-dose SWIG regimen of 5.0 mg/kg ICG we observed dose-related fluorescence quenching - referred to as "inversion" - that interfered with tumor visualization during fluorescence-guided surgery (FGS). When correlated to pre-operative MRI, a similar rim pattern was observed around the primary tumor on T₂ FLAIR, which, in retrospect, could be used as a predictor for inversion during FGS in meningioma patients receiving standard-dose ICG.

This study demonstrated that a reduced ICG dose was as effective as standard-dose SWIG in meningioma patients. We therefore recommend to adjust the standard ICG dose for meningioma patients to 2.5 mg/kg particularly when rim enhancement is observed on pre-operative T₂ FLAIR.