ESTRO 2020 Abstract Book

S481 ESTRO 2020

patients and in remaining three patients with histological confirmation. RN was scored as grade I in 15 lesions, grade II in three lesions, grade III in 13 lesions. Univariate analysis showed V5 Gy >18 cc (p 0.04), V10 Gy > 6 cc (p 0.03), median prescription dose (<18 Gy; p 0,006) and median PTV (median volume 1 cc; p 0.03) as indipendent risk factors for RN, while V12 > 4 Gy was marginally correlated with an higher risk of RN (p = 0.06). All dosimetric factors were strongly correlated, with a risk of RN of 38% for V5 Gy>18 cc, V12 Gy >4 cc, and V10Gy >6 cc. On multivariate analysis V10Gy and V12 Gy were significantly related to RN (p < 0.01). Conclusion SRS represents a feasible and effective treatment option for patients with brain metastases. A significant subset of patients may develop cerebral RN, which may eventually impact their quality of life. Dosimetric parameters of the healthy brain tissue (V5Gy, V12 Gy and V10 Gy) are strong predictors of the risk of RN and should thus be integrated in the planning process.In fact, a careful evaluation of these parameters is mandatory to limit the risk of RN and to prevent SRS- related complications. PO-0900 Radionecrosis in patients with brain metastases treated with stereotactic radiotherapy. S. Fernandez Alonso 1 , S.G. Guardado Gonzáles 1 , G. Pozo Rodríguez 2 , D. Lora Pablos 3 , J.F. Pérez-Regadera Gómez 1 1 Hospital Universitario 12 de octubre, Radiation Oncology, Madrid, Spain ; 2 Hospital Universitario 12 de octubre, Radiophysics, Madrid, Spain ; 3 Hospital Universitario 12 de octubre, Statistics, Madrid, Spain Purpose or Objective To determine the incidence of brain radionecrosis (RN) and its relation with the type of treatment received. Material and Methods 163 patients with 1-3 brain metastases were treated in our center with single-fraction radiosurgery (SF-SRS) or multi- fraction radiosurgery (MF-SRS) between 01/01/2011- 01/06/2018 and were included in this retrospective study. Patients were clinically evaluated 1 and 3 months after treatment and then every 6 months. Brain MRI was performed at 3 months after treatment and then every 6 months. RN diagnosis was radiological. Results 40% patients were men and 60% women. Mean age was 56 years. Primary tumors were lung adenocarcinoma EGFR naive (23%), other lung carcinoma (19%), triple negative breast (10%), melanoma (9%) and other histologies (39%). According RPA classification 49% was I, 50% II and 1% III. Median overall survival was 3.28 years. 51% patients had received previous cranial treatment; 65% whole brain radiotherapy (WBRT), 25% surgery and 10% surgery + WBRT. 63% patients received MF-SRS (58% 7x500 cGy, 29% 6x500 cGy and 13% another fractionation). 42% patients received SF-SRS (95% 15 Gy, 3% 18 Gy and 2% another dose). Dose was prescribed to 85% isodose line to get at least 95% target coverage of prescribed dose. Immobilization was performed in 47% with a bloody Radionics guide, in 45% with a frameless system (Brainlab mask) and in 8% with a reclining Radionics guide. RN incidence was 16%. It appeared in 22.4% of SF-SRS group and in 6.9% of MF-SRS with a median appearance of 7 months from stereotactic radiotherapy (p=0.012). Of the total cases of RN, 50% had received previous cranial irradiation (70% 10x300 cGy and 30% 14x250 cGy), however there was no relation between RN and previous cranial irradiation or surgery (p=0.371).

Conclusion There are not differences in overall survival between NSCLC patients with BMs whether the primary tumor is controlled or if it has not yet received specific treatment. PO-0899 Risk of brain Radionecrosis after radiosurgery in oligometastatic patients I. Chiovatero 1 , C. Mantovani 1 , G.C. Iorio 1 , C. Cavallin 1 , A. Vella 1 , E. Orlandi 1 , M. Cerrato 1 , S. Badellino 1 , D. Caivano 1 , M. Levis 1 , V. De Luca 1 , U. Ricardi 1 1 University of Turin, Department of Oncology, Torino, Italy Purpose or Objective To evaluate the toxicity profile of radiosurgery (SRS) focusing mainly on radionecrosis (RN) and to investigate for any clinical and dosimetric related factor in a cohort of oligometastatic brain patients. Material and Methods We retrospectively analysed the data of 75 oligometastatic patients (41 male, 34 female) with 129 lesions, treated at our Institution between 2015 and 2017. The average age at diagnosis was 64 years old. Most lesions were supratentorial (107/129), with an average volume of 3.5 cc. The primary tumor was lung cancer in 46 patients, breast cancer in 8 patients, colon-rectum cancer in 5 patients and miscellaneous in the remaining patients (16). Three patients received whole brain irradiation before SRS. In two cases a reirradiation was performed (at a median distance of 18 months after previous treatment). SRS was performed in 115 lesions with a median prescription dose (at the 80% isodose) of 21 Gy (range 16- 24 Gy), while a hypofractionated sterotactic treatment was performed in 14 lesions (24-27 Gy in three fractions in 12 lesions and 30 Gy in five fractions in two lesions). For each lesion, variables recorded included volume of brain receiving a specific dose (V5 Gy, V10 Gy, V12 Gy, V18 Gy), location/magnitude of hot spots, PTV volume, steroid therapy before treatment, concomitant systemic therapy (including immunotherapy or TKI). All patients underwent neuroradiological examination with brain MRI every three months; MRI spectroscopy and MRI perfusion were used to define a RN. RN was recorded using CTCAE scale (version 4.1). Results With a median follow-up after SRS of 12 months for surviving patients, the 1-yr local control was 82%. Twenty- seven patients showed RN on 31 treated metastases. RN was diagnoses on the basis of radiological features in 24