NIMG-39. THE “RESECTABILITY INDEX” AS A NOVEL OBJECTIVE PREDICTOR OF SURVIVAL FOR PATIENTS WITH ADULT-TYPE DIFFUSE GLIOMAS

Abstract Extent of resection (EOR) is a strong prognostic factor for patients with adult-type diffuse gliomas. Whole brain tractography (WBT) allows visualization of tumors in relation to functional subcortical white matter tracts connecting eloquent cortex. We developed a preoperative metric, the resectability index (RI), to estimate tumor resectability based on pre-resection volume (PRV) and unresectable tumor volume (UTV). We explore if RI predicts progression-free survival (PFS) and overall survival (OS). We retrospectively reviewed the charts of consecutive patients with adult-type diffuse gliomas resected from 2013-2020. Only patients with pre-operative DTI MRIs were included. UTV was the total overlapping volume of tumor with functionally significant tracts (corticospinal, arcuate, optic, fornix) and deep structures (basal ganglia, thalamus, brainstem). RI was (PRV-UTV)/PRV. Seventy-nine patients were included with an average age of 56 years at time of surgery. Glioblastoma was the most common histology (68%). Tumors were located in the left hemisphere (LH) (48%), right hemisphere (RH) (39%), and bilateral hemispheres or midline (BHM) (13%). EOR for LH, RH, and BHM tumors was 0.8, 0.91, and 0.29, respectively (P = 0.1^7). RI for LH, RH, and BHM tumors was 0.86, 0.912, and 0.44, respectively (P = 0.00021). Cox regression was used to model PFS and OS based on age, preoperative KPS, WHO grade, EOR, and RI. Age, recurrent status, bilaterality, residual tumor volume (RTV) and UTV predicted PFS (CI = 1.01 – 1.06, P = 0.002). For OS, UTV and RI were more strongly predictive than RTV or EOR. In a Cox regression model consisting only of preoperative variables, RI was independently predictive of OS. RI is a novel metric with potential efficacy for preoperative survival prognostication in patients with diffuse gliomas. RI may enable neurosurgeons to provide HGG patients with more accurate information about expected benefits of surgical intervention than is currently possible. RI will also enable more valid comparisons of HGG patient cohorts treated at different institutions.