Conventional MRI studies showed that radiation-induced brain necrosis in patients with nasopharyngeal carcinoma (NPC) in years after radiotherapy (RT) could involve brain gray matter (GM) and impair brain function. However, it is still unclear the radiation-induced brain morphological changes in NPC patients with normal-appearing GM in the early period after RT. In this study, we acquired high-resolution brain structural MRI data from three groups of patients, 22 before radiotherapy (pre-RT) NPC patients with newly diagnosed but not yet medically treated, 22 NPC patients in the early-delayed stage after radiotherapy (post-RT-ED), and 20 NPC patients in the late-delayed stage after radiotherapy (post-RT-LD), and then analyzed the radiation-induced cortical thickness alteration in NPC patients after RT. Using a vertex-wise surface-based morphometry (SBM) approach, we detected significantly decreased cortical thickness in the precentral gyrus (PreCG) in the post-RT-ED group compared to the pre-RT group. And the post-RT-LD group showed significantly increased cortical thickness in widespread brain regions, including the bilateral inferior parietal, left isthmus of the cingulate, left bank of the superior temporal sulcus and left lateral occipital regions, compared to the pre-RT group, and in the bilateral PreCG compared to the post-RT-ED group. Similar analysis with ROI-wise SBM method also found the consistent results. These results indicated that radiation-induced brain injury mainly occurred in the post-RT-LD group and the cortical thickness alterations after RT were dynamic in different periods. Our findings may reflect the pathogenesis of radiation-induced brain injury in NPC patients with normal-appearing GM and an early intervention is necessary for protecting GM during RT.
Keywords: 2D-CRT, conventional two-dimensional radiotherapy; AJCC, American Joint Committee on Cancer; ANOVA, analysis of variance; Brain injury; CMBs, cerebral microbleeds; CT, cortical thickness; Cortical thickness; DMN, default mode network; FDR, false discovery rate; FWHM, full width at half maximum; GLM, general linear model; GM, gray matter; ICC, isthmus of the cingulate cortex; IMRT, intensity-modulated radiation therapy; IPC, inferior parietal cortex; KPS, Karnofsky performance status scale; LOC, lateral occipital cortex; MTC, middle temporal cortex; NPC, nasopharyngeal carcinoma; PoCG, postcentral gyrus; PreCG, precentral gyrus; PreCUN, precuneus; RA, relative alteration; RT, radiotherapy; Radiotherapy; SBM, surface-based morphometry; STC, superior temporal cortex; Structural MRI; Surface-based morphometry; VBM, voxel-based morphometry; WM, white matter; bSTS, bank of the superior temporal sulcus; cMFC, caudal middle frontal cortex; post-RT-ED, in the early-delayed stage after radiotherapy; post-RT-LD, in the late-delayed stage after radiotherapy; pre-RT, before radiotherapy.