SURG-42. THE T1/T2 RATIO IS ASSOCIATED WITH RESECTABILITY IN PATIENTS WITH IDH-MUTANT ASTROCYTOMAS CNS WHO GRADES 2 AND 3

Abstract PURPOSE IDH-mutant astrocytomas CNS WHO grade 2 and 3 show heterogenous appearance on magnetic resonance imaging (MRI). In the pre-molecular era, the discrepancy between T1 hypointense and T2 hyperintense tumor volume in absolute values has been proposed as a marker for diffuse tumor growth. We set out to investigate if a ratio of T1 to T2 tumor volume (T1/T2 ratio) is associated with resectability and overall survival in patients with IDH-mutant astrocytomas. METHODS Patient data from two centers (Center A: Sahlgrenska University Hospital, Gothenburg, Sweden; Center B: LMU University Hospital, Munich, Germany) were collected retrospectively. Inclusion criteria were as follows: pre- and postoperative MRI scans available for volumetric analysis (I), diagnosis of an IDH-mutant astrocytoma between 2003-2021 (II), and tumor resection at initial diagnosis (III). Tumor volumes were manually segmented. The T1/T2 ratio was calculated and correlated with extent of resection, residual T2 tumor volume, and overall survival. RESULTS The study comprised 134 patients with 65 patients included from Center A and 69 patients from Center B. The median overall survival was 134 months and did not differ between the cohorts (p=0.29). Overall, the median T1/T2 ratio was 0.79 (range 0.15-1.0). Tumors displaying a T1/T2 ratio of 0.33 or lower showed significantly larger residual tumor volumes postoperatively (median 17.9 cm3 versus 4.6 cm3, p=0.03). The median extent of resection in these patients was 65% versus 90% (p=0.03). The ratio itself did not correlate with overall survival. In multivariable analyses, larger postoperative tumor volumes were associated with shorter survival times (HR 1.02, 95% CI 1.01-1.03, p<0.01). CONCLUSION The T1/T2 ratio might be a good indicator for diffuse tumor growth on MRI and is associated with resectability in patients with IDH-mutant astrocytoma. This ratio might aid to identify patients in which an oncologically relevant tumor volume reduction cannot be safely achieved.