ESTRO 2023 - Abstract Book

S1862

Digital Posters

ESTRO 2023

Purpose or Objective This study is using quantitative MRI (qMRI) for longitudinal follow-up after concomitant chemoradiotherapy (CRT) for glioma patients. The aim is to observe changes in normal appearing white matter (NAWM) in the brain and how it is related to the absorbed dose from radiotherapy. Materials and Methods NAWM were analysed for 10 patients on their follow-up MRI-scans after surgery and treatment according to the Stupp regime (60 Gy/30 fx). Patients were examined with MRI before and after surgery and every 3rd month after completed RT. In median 6 follow-up MRI were performed during the studied period of two years after RT. The qMRI sequence SyMRI MaGiC (GE Medical Systems) was added to standard protocols for brain tumour patients. Synthetic T1 and T2 images were reconstructed as well as relaxation rate maps (R1 and R2). Maps of proton density (PD) and myelin concentration was also calculated, all using the SyMRI software (SyntheticMR AB). ROI were placed in up to 16 anatomical locations for every patient, no ROI was drawn if tumour or oedema was present. MRI and dose distribution from Eclipse (Varian) were rigid registered. ROI drawing and image registration was done in MICE toolkit (NONPI Medical AB). Changes in ROI between follow-up and pre operative MR were calculated using Matlab (The MathWorks Inc.). Parameters observed were relaxation rates R1 and R2, PD and the concentration of myelin. Analyses were done in dependence on radiation dose from CRT and time after treatment.

Fig. 1: Synthetic T2-weighted image with ROI (yellow circles) placed bilateral in the lower frontal lobe and in corpus callosum. Isodose levels corresponding to 10, 20, 30, 40, 50 and 57 (95%) Gy.

Results A significant increase in PD (1.5%) between pre-operative imaging and 1st follow-up, and a corresponding decrease in myelin concentration (-2.2%) were observed. There was no significant change in R1, although a significant change (0.3 s-1) was observed in R2. In Fig. 2 the mean of difference for ROIs with different dose levels is shown as a function of time. With time and low dose, the PD-value and myelin concentration returned to baseline, while for high doses (>30 Gy) the change increased with time.