ESTRO 2021 Abstract Book

S635

ESTRO 2021

radiotherapy in their course of treatments and had a subsequent MRI follow-up of at least 6 months. Post- radiation injury, defined as new enhancing lesions on CE-T1 MRI which stabilized or decreased after at least 3 months follow-up, was delineated on the scan which showed the greatest extent. We spatially normalized the delineations to stereotaxic MNI space and performed voxel-based analysis (VBA) to compare development and absence of post-radiation injury. We corrected for multiple comparisons using family-wise error correction to eliminate false positive results. Locations of post-radiation lesions were labeled using an arterial territory map, the Harvard-Oxford cortical atlas and a white matter atlas (XTRACT). Results 33 of 101 patients developed post-radiation injury with a median volume of 7.3cc (IQR: 5.0cc – 28.2cc). VBA showed a confluent area in the left temporal region where post-radiation lesions were significantly ( P < 0.05) more often located (Fig. 1). This area of 19.5 cc included parts of the left temporal cortices (Table 1). Furthermore, the detected sensitive area was located on the border of the territories of the middle cerebral artery (MCA) and posterior cerebral artery (PCA), with a predominant distribution in the former.

Conclusion We investigated the spatial distribution of post-radiation injury and found an area in the left temporal region that significantly predisposed for development of post-radiation lesions. Additionally, this area involved the watershed area between the MCA and PCA. Further spatial exploration of post-radiation injury could help elucidate areas in the brain that are potentially vulnerable to vascular damage. This may ultimately guide radiation treatment and modality selection. PD-0802 Radionecrosis and intracranial stereotactic radiosurgery S. Fernández 1 , S. Guardado 1 , G. Pozo 2 , R. D´Ambrosi 1 , S. Pedraza 1 , C. Ramón 3 , C. Martín-Arriscado 4 , M.Á. Cabeza 1 , E. Cabello 2 , M.Á. Pérez Escutia 1 , J.F. Pérez-Regadera 1 1 12 de Octubre University Hospital, Radiation Oncology, Madrid, Spain; 2 12 de Octubre University Hospital, Radiophysics, Madrid, Spain; 3 12 de octubre University Hospital, Radiophysics, Madrid, Spain; 4 12 de Octubre University Hospital, Statistics, Madrid, Spain