Nirl-13 Histopathologic Confirmation of Tumor Recurrence Identified on Contrast Clearance Analysis Maps - A Validation Study

BACKGROUND Stereotactic radiosurgery (SRS) has become a standard modality in the treatment of brain metastases. The differentiation between adverse radiation effects (ARE) and tumor recurrence or progression is important in this setting. The advent of immunotherapy and targeted therapy often makes this distinction difficult to achieve. Contrast clearance analysis (CCA) is a useful technique that can inform clinical decisions but has so far only been histologically validated in the context of high-grade gliomas. METHODS Between 2018 and 2023, more than 200 patients who had been treated with SRS for various brain pathologies including brain metastasis, atypical meningiomas, and high-grade gliomas underwent CCA studies. Among these patients, clinical scenarios mandated surgery in 7 patients. Targeted biopsies were taken at the time of surgery in all patients. Histopathology findings were compared with the CCA findings in these patients. RESULTS All 7 patients had been treated with gamma knife radiosurgery and were being followed up with periodic MR imaging. All patients underwent CCA when the necessity to distinguish tumor recurrence from ARE/ radiation necrosis arose. Targeted biopsies showed 100% concordance of the pre-surgery CCA findings with histological findings. Viable tumor tissue was identified on pathology in all instances where the CA map indicated the presence of viable tumor represented in blue color. CONCLUSIONS Based on prior studies on GBM and the surgical findings in our series, delayed contrast extravasation MRI findings correlate well with histopathology. CCA can provide a quick diagnosis and have a direct impact on patient treatment and outcomes.