ESTRO 2021 Abstract Book

S638

ESTRO 2021

spasms during the first 3 weeks of follow-up. No acute treatment-related toxicities or spasticity relapse were reported. Conclusion the present is the first clinical report on the use of a linac-based SRS for the treatment of malignant spasticity. These preliminary results with a short follow-up documented a clinical activity of SRS that will be explored in a larger population to better assess effectiveness, toxicity, and duration of the response. PD-0805 Diffusion kurtosis imaging and white matter injury after radiotherapy of adults with brain tumours C. Skinnerup Byskov 1 , L. Haldbo-Classen 1 , A. Harbøll 2 , S. Nørhøj Jespersen 3 , J. Folsted Kallehauge 2 1 Aarhus University Hospital, Department of Oncology, Aarhus N, Denmark; 2 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus N, Denmark; 3 Aarhus University, Center for Functionally Integrative Neuroscience and Dept. of Physics and Astronomy, Aarhus C, Denmark Purpose or Objective Radiotherapy (RT) is crucial in the treatment of adults with lower-grade gliomas (LGG). The inevitable irradiation of surrounding healthy brain may cause delayed and late toxicity with severe impact on patients’ cognitive functioning and quality of life. However, the underlying mechanism of radiation induced brain injury is not fully understood. Microstructural damage such as demyelination, vascular damage and white matter (WM) injury have been proposed, but are difficult to assess with conventional magnetic resonance imaging (MRI). A novel method, diffusion kurtosis imaging (DKI) may better detect microstructural WM changes and thus serve as an early biomarker of radiation induced toxicity to healthy brain. Materials and Methods Eleven adult LGG patients referred to postoperative RT were included. RT was planned and delivered according to national guidelines (www.dnog.dk). All patients received adjuvant chemotherapy. The MRI protocol consisted of pre- and post-contrast 3D T1-weighted sequences (T1W), axial T2 fluid attenuated inversion recovery (FLAIR), sagittal T2 and a diffusion-weighted (DW) sequence including a fast, three minutes DKI sequence (Hansen, NeuroImage 2016;142:381-93). Patients were scanned before RT and 3 and 12 months after the end of RT. WM and grey matter (GM) were segmented with FreeSurfer 7.1 (Puonti, NeuroImage 2016;143:235-249) on the pre-treatment T1W MRI and rigidly co-registered to radiation dose distributions and follow-up scans. Mean diffusivity (MD) and mean kurtosis (MK) was calculated from the DKI scan in WM and GM for voxels receiving radiation dose between 0 and 45 Gy. Differences were analysed using Wilcoxon signed rank test and considered significant if p < 0.05. Results Six patients (oligodendroglioma grade 2 (n=2), anaplastic oligodendroglioma (n=2), diffuse astrocytoma (n=1) and anaplastic astrocytoma (n=1)) were available for analysis. The median age was 52.5 years (33-64 years). The most common tumour location was frontal lobe (n=5) and the remaining was parietal lobe (n=1). Patients were treated with photons (n=3) or protons (n=3) to a prescribed dose of 50.4 Gy (n=3) and 59.4 Gy (n=3) using a relative biological effect of 1.1 in the proton plans. Pre-treatment median MD for GM and WM was 1.35 (1.18 - 1.47) µm 2 /ms and 1.01 (0.96 - 1.05) µm 2 /ms, respectively. The respective median MD increased to 1.44 (1.33-1.68, p=0.03) µm 2 /ms and 1.04 (0.98-1.15, p=0.03) µm 2 /ms for GM and WM at 12 months post RT (Figure 1). No significant difference was found for MK of GM and WM. We observed an increase in ventricle volume after RT (median volume of lateral ventricles 28.9 cm 3 compared to 40.4 cm 3 , p=0.02), which may impact the results. In future analyses, the segmentation of WM and GM will be done for each MRI scan to avoid errors due