(P 62) INTRAOPERATIVE BONE AND SOFT TISSUE TUMOR MARGIN IDENTIFICATION WITH FLUORESCENCE LIFETIME (FLT) IMAGING

Objective: Surgical margin status is a critical predictor of sarcoma outcomes, and despite optimal resections and thorough intraoperative pathologic assessment, residual positive margins can persist and complicate clinical management. Fluorescence-guided surgery using indocyanine green (ICG) is a promising tool to aid intraoperative margin assessment. However non-specific dye uptake is a major problem that reduces sensitivity and specificity. We evaluated the accuracy of FLT imaging to identify tumor margins in benign and malignant bone and soft tissue tumors.

Methods: Patients undergoing surgery of various sarcomas (n=43), including Leiomyosarcoma, chondrosarcoma, and chordoma received a preoperative injection with ICG a few hours prior to surgery, in doses of 0.5mg/kg (n=15), 1mg/kg (n=15) and 1.5mg/kg (n=13). Representative tumor samples were next analyzed using FLT microscopy and sensitivity and specificity were calculated against histology, using pixel-wise and specimen-wise analysis.

Results: The uptake and mean FLT of ICG strongly depended on the radiation status of the tumor, with necrotic/non-viable tumor regions showing either low ICG uptake or markedly shorter FLT (0.56ns) compared to viable tumor (0.65ns). In addition, normal muscles, adipose tissue and bone showed shorter FLT (0.57ns) than viable tumors. A preliminary specimen-level analysis (n = 33) suggests that FLT improves tumor delineation accuracy (70 - 90%) compared to fluorescence intensity ( < 50%).

Conclusion: Our results show that FLT outperforms fluorescence intensity for identifying sarcoma margins in patients injected with ICG a few hours before surgery. While same day injections are clinically more feasible, longer injection intervals should significantly improve accuracy. Ongoing work is focused on studying more detailed ICG dosage and timing dependence of FLT imaging accuracy, and on evaluating real-time intraoperative FLT imaging during sarcoma surgeries.