Overestimation of grey matter atrophy in glioblastoma patients following radio(chemo)therapy

Objective
Brain atrophy has the potential to become a biomarker for severity of radiation-induced side-effects. Particularly brain tumour patients can show great MRI signal changes over time caused by e.g. oedema, tumour progress or necrosis. The goal of this study was to investigate if such changes affect the segmentation accuracy of normal appearing brain and thus influence longitudinal volumetric measurements.
Materials and Methods
T1-weighted MR images of 52 glioblastoma patients with unilateral tumours acquired before and three months after the end of radio(chemo)therapy were analysed. GM and WM volumes in the contralateral hemisphere were compared between segmenting the whole brain (full) and the contralateral hemisphere only (cl) with SPM and FSL. Relative GM and WM volumes were compared using paired t-tests and correlated with the corresponding mean dose in GM and WM, respectively.
Results
Mean GM atrophy was significantly higher for full segmentation compared to cl segmentation when using SPM (mean ± std: ΔVGM,full = -3.1% ± 3.7%, ΔVGM,cl = -1.6% ± 2.7%; p < 0.001 , d = 0.62). GM atrophy was significantly correlated with the mean GM dose with the SPM cl segmentation (r = -0.4, p = 0.004), FSL full segmentation (r = -0.4, p = 0.004) and FSL cl segmentation (r = -0.35, p = 0.012) but not with the SPM full segmentation (r = -0.23, p = 0.1).
Conclusions
For accurate normal tissue volume measurements in brain tumour patients using SPM, abnormal tissue needs to be masked prior to segmentation, however, this is not necessary when using FSL.