ESTRO 2020 Abstract Book

S479 ESTRO 2020

Results 118 patients (with a total of 139 tumors) underwent SRS for brain metastases in our hospital during that period. 12 of them (8,6%) had RN. The most common primary tumor was lung adenocarcinoma (45,3%), the mean size was 16mm, the mean dose 19,2Gy, the mean time of RN diagnosis from SRS was 15,5 months. 8,6% had previous surgery and 46% WBRT. We found no significant statistical association, between possible risk factors and RN. However a difference of 2.8 mm in tumor size was observed, with an inclination to be larger in RN group (p=0.14) The median OS among patients with RN was 21.3 months and among non RN 13.7 months, with no significant differences (p=0.15).

BrainMetGPA application was used to calculate the estimated survival expectancy. Results 112 patients underwent SRS during that period. The most common primary tumor was lung adenocarcinoma (46,6%), followed by breast cancer(10,7%), the mean size was 16mm, the mean dose 19,2Gy. 11,6% had previous surgery and 41,1% WBRT. Median OS was 15 months. We found statistically significant differences between OS and previous surgery HR 3.206 IC95% (1.16, 8.8)(P=0.024). The agreement between the GPA and the OS was very low (ICC: 0.25). 50% of the patients had 8 months of difference in survival between the estimated and the observed.

Conclusion The GPA does not give an accurate estimation of the survival for our patients with brain metastases treated with SRS PO-0896 Radionecrosis in brain metastases treated with Stereotactic radiosurgery M.A. Rodriguez Medizabal 1 , M. Rico 1 , S. Flamarique 1 , M. Campo 1 , A. Martin 1 , L.O. Rosas 1 , E. Martinez 1 , M. Barrado 1 , S. Pellejero 2 , F. Mañeru 2 1 Complejo hospitalario de Navarra, Radiation Oncology, Pamplona, Spain ; 2 Complejo hospitalario de Navarra, Radiophysics, Pamplona, Spain Purpose or Objective Our main objective was to estimate the incidence and risk factors for radionecrosis (RN) and overall survival (OS) in a cohort of patients with brain metastases treated with Stereotactic radiosurgery (SRS). Material and Methods We retrospectively reviewed patients treated with SRS for brain metastases between January 2011 and December 2018. All RN were diagnosed by RM .We used T-test, Fisher test and Chi2 to analyzed possible risk factors: age, size, dose, previous surgery and previous whole brain radiotherapy (WBRT). We used Kaplan-Meier and Log-rank test to analyze OS.

Conclusion We found no statistically significant associations between risk factors and radionecrosis, neither in survival between patients with and without necrosis, which could be partly due to the few cases of RN. With some more sample, statistically meaningful differences could be found. PO-0897 Dosimetric Consequence of Transient Post- Surgical Anatomical Effects for Glioblastoma M. Tyyger 1 , M. Nix 1 , L. Murray 1,2 , S. Currie 3 , C. Nallathambi 1 , R. Speight 1 , B. Al-Qaisieh 1 1 Leeds Cancer Centre, Leeds Teaching Hospitals NHS Trust, Leeds, United Kingdom ; 2 Radiotherapy Research Group, University of Leeds, Leeds, United Kingdom ; 3 Department of Neuroradiology, Leeds Teaching Hospitals NHS Trust, Leeds, United Kingdom Purpose or Objective This investigation aimed to quantify volumetric and dosimetric effects of employing <72-hour post-surgical assessment MRI, in contrast to 1 week delayed imaging for radiotherapy delineation. Exploitation of post-surgical assessment MRI for glioblastoma (GBM) delineation eradicates the necessity of acquiring an additional delayed MRI at time of CT- simulation. However, transient peritumoural oedema/inflammation and increased time for progression limits the reliability of post-surgical delineations to accurately represent tumour extent at treatment.