Fig. 3. Representative cases illustrating the association between radiation-induced LEP on 6-month follow-up imaging and changes in the DTI-ALPS index. A 75-year-old male patient with lung cancer underwent WBRT for multiple brain metastases (not shown in these slices). The DTI-ALPS index decreased by 21.1%, from 1.703 at baseline to 1.344 at 1 month post-WBRT. Compared to the baseline FLAIR image (A), the development of LEP is evident on the 6-month follow-up FLAIR image (B). A 66-year-old male patient with lung cancer underwent WBRT for multiple brain metastases (not shown in these slices). The DTI-ALPS index decreased by 1.19%, from 1.426 at baseline to 1.409, 1 month post-WBRT. Compared to the baseline FLAIR image (C), no LEP was observed on the 6-month follow-up FLAIR image (D). DTI-ALPS, diffusion tensor imaging analysis along the perivascular space; WBRT, whole-brain radiotherapy. LEP, leukoencephalopathy; DTI-ALPS, diffusion tensor imaging analysis along the perivascular space; WBRT, whole-brain radiotherapy; FLAIR, fluid-attenuated inversion recovery.