A Shift from Brain Volume to Cerebrospinal Fluid Volume after Radiotherapy: Loss of Tissue after Treatment for Brain Tumors

Abstract

Healthy brain tissue shows dose-dependent atrophy after radiotherapy (RT) for brain tumors. One of the most challenging consequences of this phenomenon is post-RT cognitive decline. Changes in areas associated with cognitive functions, such as the hippocampus and cerebral cortex, have already been linked to the applied dose and cognitive outcomes. In volumetric analyses in aging and degenerative brain diseases, certain regions in both gray and white matter undergo volume loss after RT. However, the total volume within the cranium is not expected to change, as previous studies have already shown that the total intracranial volume (TIV) remains the same. Instead, the total brain volume decreases, with a converse increase in cerebrospinal fluid volume (CSF). For radiotherapy, this phenomenon has not yet been researched. We therefore performed a volumetric analysis of the brain, to verify that the TIV remains the same, and to see whether there is a shift in volume ratio of tissue and CSF. We included 28 patients undergoing radiotherapy for glioma with adequate MRI scans at baseline and 1 year after start of therapy. The brain was automatically segmented into white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF) using SPM12 and CAT12. Volumes of each region were computed, as well as the ratio between total brain tissue volume (GM+WM) and TIV. Differences in pre-RT and post-RT volume were examined with a paired Wilcoxon signed rank test, with p < 0.05 as the threshold of statistical significance. Mean volumes and the post-RT changes in each area are shown in the table. Significant changes are seen in all brain regions, with GM and WM showing decrease, and CSF showing increase. The total intracranial volume did not change between the two MRI scans. The ratio of total brain tissue volume and TIV changed as well, going from a median of 80.0% to 75.7% (p = 0.03). Both gray matter and white matter volumes are affected by radiotherapy, showing a decrease in volume after one year. As the total intracranial volume does not change, the cerebrospinal fluid volume increases, as the tissue volume loss is replaced by CSF. This effect is also seen in healthy ageing and degenerative brain disease, suggesting the cognitive decline after RT could have a similar link to brain volume.Abstract 3617; TableRegionMedian pre-RT volume (cc)Median volume difference (cc)95% CI of differencep-valueTotal intracranial volume1386.12.2-11.0 – 17.60.81Gray matter608.2-12.8-24.8 – -4.7< 0.01White matter520.6-30.0-42.0 – -20.1< 0.01Cerebrospinal fluid288.044.321.3 – 75.5< 0.01 Open table in a new tab