ESTRO 2020 Abstract Book

S466 ESTRO 2020

radiation lesions on follow-up magnetic resonance imaging (MRI) after (chemo-)radiotherapy in a retrospective database of 144 adult cases of WHO grade II-IV gliomas. Post-radiation lesions were investigated with regard to occurrence and location of postoperative ischemia, as well as in relation to the received dose of radiotherapy. Results Incidence of post-radiation injury after first surgery did not differ between patients with and without postoperative ischemia ( P = 0.846). However, postoperative ischemia after re-resection of a recurrent glioma occurred significantly less in patients with prior post-radiation injury, as opposed to absence of post- radiation injury ( P = 0.023) (figure 2). Investigation of the spatial relation between postoperative ischemia and post- radiation injury showed overlap in 10 of 16 patients (62.5%) in the case of first surgery, and no overlap in the single case of re-resection. Planned radiation dose nor EQD2 was significantly related to post-radiation injury in our population ( P = 0.208 and P = 0.323, respectively). In line with literature, post-radiation injury occurred significantly more in patients receiving additional chemotherapy (p = 0.023). Conclusion The occurrence of post-operative ischemia after first surgery did not predict the development of post-radiation injury. Presence of prior post-radiation injury at recurrence was associated with less postoperative ischemia after re-resection in patients with a recurrent grade II-IV glioma. No evident spatial relation between post-radiation injury and postoperative ischemia was found. A better understanding of the effects of glioma treatment on the surrounding vascular status might provide more insight in the development of treatment complications in glioma patients.

PO-0867 Risk of Symptomatic Radiation Necrosis Following Stereotactic Radiosurgery for Brain Metastases M. Sayan 1 , B. Şahin 2 , T. Zoto Mustafayev 2 , E.Ş. Sare Kefelioğlu 2 , I. Vergalasova 1 , A. Gupta 1 , A. Balmuk 2 , G. Güngör 2 , N. Ohri 1 , J. Weiner 1 , E. Karaarslan 3 , E. Özyar 2 , B. Atalar 2 1 Rutgers Cancer Institute of New Jersey, Radiation Oncology, New Brunswick, USA ; 2 Mehmet Ali Aydınlar Acıbadem University, Radiation Oncology, Istanbul, Turkey ; 3 Mehmet Ali Aydınlar Acıbadem University, Radiology, Istanbul, Turkey Purpose or Objective Stereotactic radiosurgery (SRS) has become an increasingly utilized treatment option in the initial management of patients with brain metastases. While its efficacy is well documented, treatment related complications, particularly symptomatic radiation necrosis (RN), remains as an obstacle for wider implementation of this treatment modality. We examined risk factors associated with the development of symptomatic RN in patients treated with SRS for brain metastases. Material and Methods We performed a retrospective review of our institutional database to identify patients with brain metastases treated with SRS. We excluded patients who received prior SRS to the same metastatic lesion, though prior whole brain radiation (WBRT) was allowed. Both the development of new neurologic complaints requiring intervention, such as steroid therapy, bevacizumab, or surgery, and radiographic evidence of RN on serial MRI were required for the diagnosis of symptomatic RN. Dosimetry data were collected, and the Wilcoxon rank sum test was used to identify predictors of symptomatic RN. Results We identified 323 brain metastases treated with SRS in 170 patients from 2009 to 2018. The mean prescription dose was 22 Gy (range, 12-27.5 Gy) in 1 to 5 fractions. WBRT was received by 31% of the patients either before or after SRS. Thirteen patients (4%) experienced symptomatic RN after treatment of 23 (7%) lesions. After SRS, the median time to RN was 8.3 months. In patients with symptomatic RN, the median target volume, conformity index, coverage, normalization, V10 Gy, and V12 Gy was 7.6 cm 3 (range, 0.7-52.92 cm 3 ), 1.5 (range, 0.9-7.9), 97.4% (range, 91-100%), 85% (range, 63-90%), 28.9 cm 3 (range, 4.1-114.7 cm 3 ), and 24 cm 3 (range, 3.3-85.1 cm 3 ), respectively. Patients with symptomatic RN had a larger mean target volume (p<0.0001), and thus larger V100% (p<0.0001),