OP03BORDER TRANSITION ACROSS THE INVASIVE MARGIN OF GLIOBLASTOMAS DO NOT PROVIDE MEASURES OF TUMOUR INVASION: A DIFFUSION TENSOR STUDY.

INTRODUCTION: Invasion is a cardinal feature of glioblastomas - diffusely invasive tumours have worse prognosis than less invasive gliomas. Diffusion tensor imaging (DTI) provides a non-invasive method of studying the invasive margin. Studies measuring diffusion changes across the tumour margin, a measure of changes of cellularity, suggest it may be a marker of invasiveness. In this study we have assessed isotropic diffusion changes across the DTI defined tumour margin. METHOD: 47 patients with glioblastomas were studied before 5-ALA guided resection of these tumours before starting chemoradiotherapy. Imaging included anatomical imaging and DTI - which was processed into isotropic (p) and anisotropic (q) components. The area with the largest separation of the p and q was selected as the most invasive region and a line drawn across the border of p (the marginbetween invasive tumour and normal brain). The transition was quantified by the border transition gradient measured from the slope of point either side of the marginas well as whether the p values were more than12% above normal brain at the margin. These values were compared with time to progression (TTP). RESULTS: There was no correlation between the border transition gradient across the marginand TTP (r= 0.3, P = 0.85). There was an increased TTP where the p values were below threshold at the margin, but this was not significant (424 days vs. 326 days; P = 0.74). CONCLUSION: Transitional measurements across the DTI defined invasive margindo not provide information on the invasive nature of tumours and the time to progression.