The following is a summary of “Diffusion decrease in normal-appearing white matter structures following photon or proton irradiation indicates differences in regional radiosensitivity,” published in the July 2024 issue of Oncology by Witzmann et al.

Radio(chemo)therapy (RCT), a standard treatment for patients with glioma, invariably results in radiation exposure to the tumor-surrounding normal-appearing (NA) tissues. The impact of radiotherapy on brain microstructure can be evaluated using magnetic resonance imaging (MRI) with diffusion tensor imaging (DTI). This study aimed to analyze regional DTI changes in white matter (WM) structures and determine their dose- and time-dependency.

As part of a longitudinal prospective clinical study (NCT02824731), MRI data were collected from 23 patients with glioma treated with either proton or photon beam therapy at three-month intervals for up to 36 months post-irradiation. Metrics including mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD), and fractional anisotropy (FA) were examined in the NA tissue of 15 WM structures. The dependence of these metrics on radiation dose, follow-up time, and distance to the clinical target volume (CTV) was analyzed using a multivariate linear regression model. Due to the small and non-comparable patient numbers for proton and photon beam irradiation, a separate assessment per treatment modality was not conducted.

About 4 WM structures—the internal capsule, corona radiata, posterior thalamic radiation, and superior longitudinal fasciculus—exhibited statistically significant decreases in RD and MD post-radiotherapy, while decreases in AD and increases in FA were less frequent. The posterior thalamic radiation displayed the most pronounced changes following RCT, with ΔRD = −8.51% (p = 0.012) and ΔMD = −6.14% (p = 0.012). These DTI changes were significantly correlated with mean radiation dose and follow-up time.

Significant DTI changes were observed in WM substructures even at low radiation doses, highlighting the potential need for new radiation dose constraints to protect these vulnerable structures and mitigate subsequent side effects. These findings underscore the importance of considering regional radiosensitivity when planning radiotherapy to minimize damage to critical brain tissues.

Source: sciencedirect.com/science/article/pii/S0167814024007291