186 Chapter 7 Figure 4. Violin plots of the pre- and post-radiotherapy values within different edema regions. Edema regions encompass any region with edema either pre- or post-radiotherapy. New edema indicates those areas with edema exclusively at post-radiotherapy and old edema indicates those areas with edema exclusively at pre-radiotherapy. Asterisks indicate significant differences. Dose-related changes Changes in the MRI metrics from pre- to post-radiotherapy were compared between healthy appearing brain regions that had received low, medium and high radiotherapy dose (Figure 6). Differences between dose groups were assessed using Wilcoxon signed-rank tests, which indicated none of the dose regions significantly differed from each other for any of the MRI metrics. In addition to the ROI dose comparison, repeated measures correlations were performed between the dose and the change each MRI metric post-radiotherapy using the dose binned ROIs (Figure 7). The changes in OEF post-radiotherapy were not related to the delivered radiotherapy dose (rrm = -0.004, p = .954). There was a significant negativerelationship between the delivered dose and the postradiotherapy changes in healthy appearing brain tissue regarding CBF (rrm = -0.286, p <.001), CMRO2 (rrm = -0.254, p = .001) and CVR (rrm = -0.346, p < . 001). This indicates that post-radiotherapy declines in CBF, CMRO2 and CVR were related to higher delivered radiotherapy dose. Additionally, voxel-wise Spearman Rank correlations between the delivered radiotherapy dose and post-radiotherapy changes in OEF, CBF, CMRO2 and CVR were performed for each individual (Supplementary Figure 4). One-sample Wilcoxon signed-rank tests indicated that the correlation values did not significantly differ from zero on the group-level (all p > .05).
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