PATTERNS OF INfiLTRATION AND RELAPSE OF GLIOBLASTOMA INVOLVING THE ANTERIOR TEMPORAL LOBE: IMPLICATIONS FOR RADIATION THERAPY TARGET VOLUME DELINEATION

Abstract

Abstract AIMS To characterise specific patterns of infiltration and recurrence for IDH-wildtype Glioblastoma (GBMwt) involving the anterior temporal lobe (ATL) METHOD Patients managed for GBMwt involving ATL between 1/2008-12/2020 were identified. Tumour was segmentated on T1-gadolinium-enhanced(T1gd) and T2-weighted(T2) sequences at baseline and initial relapse. Involvement of adjacent normal structures was assessed: superior temporal gyrus (STG), middle temporal gyrus (MTG), medial occipito-temporal gyrus (MOTG), amygdala, and uncus. Abnormalities in para- hippocampal region (PHG) and sub-insular regions were recorded; as well as distant sites of insular cortex, extreme/external/internal capsule, and frontal lobe. Two major neural pathways were also assessed: the uncinate fasciculus-inferior fronto-occipital fasciculus (UF- IFOF) and hippocampal formation (HP-PHG). RESULTS Of 562 patients 53 involved ATL with 47 included for analysis. Median volume at diagnosis on T1gd and T2 was 36cm3(IQR 12-54) and 51cm3(IQR 23-73) respectively. Adjacent sites involved on T1gd were STG/MTG (87%), amygdala (45%), uncus (8%), MOTG (4%). T2 abnormality extended into insular region in 91%, and hippocampal region in 17% patients. The temporal horn was involved in 21% and compressed/displaced in 63% of patients. Forty patients relapsed with relapse-free survival of 11.4 months. Thirty-five (87%) had T1gd relapse involving a neural pathway: UF-IFOF (74%), HP-PHG (14%), combined (9%), optic tract (3%). Twenty relapses (50%) involved distant sites in external capsule or frontal lobe. Although adjacent to ATL, no relapse occurred posterior to temporal horn or along HP-PHG unless evidence of T2 abnormality was present at diagnosis. All 8 relapses involving the HP-PHG, and none of 26 relapses involving UF-IFOF alone, had T2 involvement of HP-PHG at diagnosis. CONCLUSIONS Infiltration and relapse of GBMwt involving ATL correlates with distinct neural pathways.