Diffusion and perfusion weighted magnetic resonance imaging for tumor volume definition in radiotherapy of brain tumors
To analyse the role of MR diffusion-tensor imaging (DTI) and perfusion-weighted imaging (PWI) in characterising tumour boundaries in patients with glioblastoma multiforme. Seventeen patients with surgically treated WHO IV grade gliomas who were candidates for adjuvant chemo-radiotherapy were enrolled. Before (T0) and after radiation treatment (T1), they underwent DTI and PWI, and the apparent diffusion coefficient (ADC), fractional anisotropy (FA) and relative cerebral blood volume (rCBV) in the enhancing tumour, the hyperintense tissue adjacent to the enhancing tumour, and the normal-appearing white matter (NAWM) adjacent to the hyperintense areas were analysed. The enhancing tissue at T1 was retrospectively divided on the basis of whether or not it was also enhancing at T0. The controls were the corresponding contralateral areas, on which we normalized the rCBV values, calculating the rCBV ratio. In NAWM, we did not find any significant differences in FA, ADC or rCBV. In the hyperintense perilesional regions, FA was significantly lower and ADC significantly higher than in the unaffected contralateral tissue; there were no significant differences in the rCBV maps. The values of FA, ADC and rCBV in enhancing neoplastic tissue were all significantly different from those observed in the contralateral tissue. There was no significant difference in rCBV values between the areas enhancing at T0 and those not enhancing at T0 but enhancing at T1, which may indicate the neoplastic transformation of apparently normal brain tissue. DTI metrics identify ultrastructural changes in hyperintense perilesional areas, but these are not specific for neoplastic tissue. rCBV seemed to reflect an ultrastructural alteration that was not visible at T0, but became visible (as neoplastic progression) on conventional MR images at T1. These findings could help identify tissue at risk of tumour infiltration.