Progressive alterations of perilesional brain tissue after Gamma Knife stereotactic radiosurgery: a diffusion tensor imaging study

Introduction: To search for microstructural lesions of normal-appearing cerebral white matter surrounding a tumor or a vascular lesion, after single-fraction stereotactic Gamma Knife (GK) radiosurgery. Methods: In 43 patients with different brain lesions, magnetic resonance including diffusion tensor imaging (DTI) was performed before and after GK radiosurgery and change of parameters was measured in areas surrounding the lesion. Results: Outside the lesion, there was an increase in mean diffusivity (MD) and radial diffusivity (RD) between 2.1% and 3.4% in the 15–10 Gy and in the 10–5 Gy perilesional isodose volumes, which reached statistical significance (paired t -test) for the MD and RD values in both volumes (P≤0.05) and correlated to the delay from treatment (P<0.01 resp. P<0.05). The only significant change in the fractional anisotropy values was a decrease in the 10–5 Gy isodose volume (P≤0.01), which correlated to the radiation dose applied (P<0.05). Conclusion: We report some minor, but nevertheless significant changes in DTI parameters in normal-appearing perilesional brain tissue after GK radiosurgery progressing with time, which partially may be induced by the radiation itself and partially may be due to indirect effects of lesion reactions to the radiation. Follow-up studies are necessary for further characterization of these changes and assessment of their time course.