1155 Fluorescence Lifetime Imaging (FLIm) Provides Highly Accurate, Dye-free Tumor Margin Detection During Resection of Low Grade Gliomas

INTRODUCTION: Fluorescence guided tumor margin detection is an important tool to enhance the extent of surgical resection for gliomas. Unfortunately, low-grade tumors do not take up and metabolize dyes, such as 5-ALA, like GBM. We have developed a novel laser scanning probe to assess tissue autofluorescence decay (lifetime) which allows tumor margin detection without exogenous dyes and under normal room light conditions. METHODS: Patients undergoing routine craniotomy for resection of non-enhancing infiltrating glial tumors were enrolled in this study under local IRB approval. During resection of the final tumor margin, multiple 1x1 mm regions of the cavity were scanned with FLIm to obtain spectral measurements from tissue of interest. These regions were then biopsied and evaluated by a neuropathologist. FLIm data and ground truth pathology were processed by a machine-learning algorithm to develop classifiers for the FLIm data. Classifiers were then applied to the full data set to determine the accuracy of FLIm predictions. RESULTS: 12 patients with non-enhancing infiltrating gliomas were enrolled, with a total of 77 biopsy specimens obtained. Sensitivity of FLIm for detection of residual tumor was 0.89 (95% CI 0.8-0.98) with a specificity of 0.92 (95% CI 0.86-0.97). This resulted in a positive predictive value of 0.76 (0.58-0.94) and negative predictive value of 0.96 (0.92-1.0) with an overall accuracy of 0.91 (0.86-0.96). CONCLUSIONS: FLIm can distinguish between residual low-grade glioma and normal brain at resection margins with very high sensitivity and specificity. In addition, this quantitative technology does not require administration of exogenous dyes or other pre-operative planning, and can be used under normal room light illumination. We believe use of this technology can substantially improve the extent of resection for low-grade gliomas.