A–C: Intergroup comparison of CMB cumulative prevalence (A), mean number per patient (B), and anatomic distribution (C), demonstrating no significant differences between XRT (blue color) and PRT (orange color) groups. D: Correlative spatial analysis in a PRT-treated patient, depicting the CT-based radiotherapy dose distribution plan (left panel), an axial SWI MRI (middle panel) displaying CMB lesions (black arrows), and a corresponding overlay (right panel) which demonstrates preferential CMB enrichment along the radiation field margin. E–F: Schematic (E) and graphical (F) illustration of significant intergroup differences in CMB distribution (ie, in the main radiation field (RF), at the RF margin, or remote to the RF), suggesting PRT-associated CMB clustering at the RF margin and greater remote CMB development following XRT. G: T1 + contrast MRI (left) demonstrating a small nodular enhancement focus (white arrow) located in the left periventricular white matter (splenium), manifesting at 10 months post-PRT, consistent with TN (clinical course ruled out tumor given indolent nature of the lesion). Radiotherapy dose distribution overlay on axial computed tomography (right) demonstrates prior exposure of this region of interest to the main radiation field (56.2 Gy; orange line) and proximity to the distal fall-off region. H: Cumulative TN incidence following PRT vs XRT up until 30 years post-radiotherapy. Mean and SEM are given unless otherwise stated.