Quantitative white matter alterations of the anterior visual pathway predict injury following radiotherapy for nasopharyngeal carcinoma: a high-angular-resolution diffusion imaging study.

Abstract

Objective: This study aimed to use high-angular-resolution diffusion imaging (HARDI) to evaluate microstructural alterations and temporal evolution patterns in the anterior visual pathway (AVP) white matter of patients with nasopharyngeal carcinoma (NPC) following radiotherapy (RT).

Methods: 150 patients with nasopharyngeal carcinoma (NPC) were retrospectively enrolled and stratified into four groups according to the post-radiotherapy (post-RT) interval: G0 (pre-RT, n = 39), G1 (< 1 month post-RT, n = 30), G2 (< 6 months post-RT, n = 33), and G3 (> 6 months post-RT, n = 48). Based on high-angular-resolution diffusion imaging (HARDI), generalized q-sampling imaging (GQI) reconstruction was performed to derive GQI parameters for the anterior visual pathway, including generalized fractional anisotropy (GFA) and normalized quantitative anisotropy (NQA). Corresponding diffusion tensor imaging (DTI) parameters, including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD), were also obtained. One-way analysis of variance (ANOVA) was used to compare all parameters across the four groups, followed by post hoc pairwise comparisons. Cohen's d was calculated to assess the effect size of each parameter relative to pre-RT values.

Results: Compared with the G0 group, fractional anisotropy (FA) and normalized quantitative anisotropy (NQA) values were significantly decreased in G1 (P < 0.05). Conversely, mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) values were significantly increased bilaterally in G1 (P < 0.05). No significant differences were observed in other post-RT groups. No significant differences in generalized fractional anisotropy (GFA) values were observed between the pre-RT and any post-RT groups. Compared with the G0 group, effect-size analysis demonstrated that the largest effect sizes were present in G1. Effect sizes were generally smaller in G2. In G3, effect sizes were predominantly small to moderate.

Conclusions: DTI and GQI together exhibit the potential to serve as a biomarker of detecting microstructural alterations in the white matter of the anterior visual pathway before visible changes appear on conventional MR images, enabling a better understanding of radiation-induced injury.