Defining the optimal millimeter threshold for target lesion inclusion in the Response Assessment in Neuro-Oncology for Brain Metastases (RANO-BM) based on outcome prediction.

e14003 Background: The Response Assessment in Neuro-Oncology for Brain Metastases (RANO-BM) is the standard for therapeutic response assessment in brain metastases (BM) patients. The criteria relies on a human reader to annotate target (≥10 mm) and non-target (<10mm) lesions of interest based on unidimensional measurement of lesion diameter on brain MRI. The change in the sum largest axial diameter of 5 target lesions (RANO-BM diameter) is then used to categorize intracranial response into 4 categories: complete response (CR), partial response (PR), stable disease (SD) and progressive disease (PD). Methods: Automating the RANO-BM criteria (AUTO-RANO-BM) has enabled the rapid modulation of the threshold diameter required for inclusion of a brain metastasis as a target lesion. In this study, diameters below the RANO-BM 10mm recommendation were utilized when calculating the RANO-BM diameter. The ability of the RANO-BM diameter to predict overall survival for BM patients was then evaluated in a Cox Proportional Hazards model. In a cohort of 175 immunotherapy-treated BM patients, the optimal threshold for the RANO-BM diameter as measured by Concordance Index (C-Index) was 5mm, suggesting that the RANO-BM criteria should be amended.