We used multi-b-value diffusion models to characterize microstructural white matter changes after brain radiation into fast and slow components, in order to better understand the pathophysiology of radiation-induced tissue damage.Methods
Fourteen patients were included in this retrospective analysis with imaging prior to, and at 1, 4–5, and 9–10 months after radiotherapy (RT). Diffusion signal decay within brain white matter was fit to a biexponential model to separate changes within the slow and fast components. Linear mixed-effects models were used to obtain estimates of the effect of radiation dose and time on the model parameters.Results
We found an increase of 0.11 × 10−4 and 0.14 × 10−4 mm2/s in the fast diffusion coefficient per unit dose–time (Gy-month) in the longitudinal and transverse directions, respectively. By contrast, the longitudinal slow diffusion coefficient decreased independently of dose, by 0.18 × 10−4, 0.16 × 10−4, and 0.098 × 10−4 mm2/s at 1, 4, and 9 months post-RT, respectively.Conclusions
Radiation-induced white matter changes in the first year following RT are driven by dose-dependent increases in the fast component and dose-independent decreases in the slow component.