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contrast uptake) was having the best matrices with AUC being 0.939 and 0.991 in TC and VC respectively. ROC curve generated a cut off value of 13.3 for sensitivity and specificity of >85%, using which when implemented for VC had a diagnostic test accuracy of 94%. Nomogram for group 4 (features used-tumor location on vertical aspect, brainstem involvement, contrast uptake, oedema and calcification) was having AUC value of 0.851 in TC with lesser degree of reliability (AUC in VC-0.788). Conclusion SHH and group 4 MB can be predicted in the pre- operative setting using subgroup specific nomograms with high accuracy. PO-0713 Fractionated stereotactic radiotherapy for pituitary adenomas I. Tovar Martin 1 , M. Zurita Herrera 1 , P. Vargas Arrabal 1 , P. Galván Banqueri 1 , R. Guerrero Tejada 1 , S. Rodríguez Pavón 1 , A. Ruiz Martínez 1 , R. Ching López 1 , J. Expósito Hernández 1 , R. Del Moral Ávila 1 1 Hospital Universitario Virgen de las Nieves, Radiation Oncology, Granada, Spain Purpose or Objective Retrospective review of patients with pituitary adenomas who have been treated by fractionated stereotactic radiotherapy at our department. Material and Methods Between April of 2005 and December of 2014 we have treated 181 patients. 52% of cases were functional adenomas and, 48% non-functional adneomas. 40% of patients were men and 60% women. The median age was 44 years. The main indication for radiotherapy was postoperative residual tumor in 47.5%, with closeness of the optical nerves or chiasm in 75.2% of cases. The schedule of treatment was 50Gy at 2Gy per fraction, in all patients. Results The median of follow up was 50 months. At the end of the study 53.5% of the patients presented disease stabilization, 39,6% decrease of the tumor size and 5,9% complete response. Only 1% of the patients had disease progression. Related to clinical situation 63,2% of the patients related the same symptom as before the treatment, and 30,5% had improvement of their quality of live. Only 6,3% of the patients had worsening of their symptoms. Between cases with functioning adenomas 24,5% of patients reduced their endocrine treatment, only 18,9% of patients increased their treatment, the remainder had the same treatment. No acute toxicity was reported in 66% of the patients. The most frequent one was headache (21%), mainly grade 1 (84,8%), no grade 3 or higher toxicity was recorded. In the 89,1% not late toxicity was reported. Conclusion Fractionated Stereotactic Radiotherapy is a modality of treatment good tolerated and with excellent local control. PO-0714 A Radiosensitivity and PD-L1 Predict Clinical Outcome of Patients with GBM in TCGA Dataset B.S. Jang 1 , I.A. Kim 2 1 Seoul National University Hospital, Radiation Oncology, Seoul, Korea Republic of 2 Seoul National College of Medicine, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective Background : Radiotherapy plays a major role in treating glioblastoma (GBM). Combination of radiotherapy and immune checkpoint blockade such as anti-PD-L1/PD-1 inhibitor has emerged as a promising strategy and been being actively tested in clinical trial setting. In this study, we tried to characterize a specific group that would

potentially benefit from this combination strategy using The Cancer Genome Atlas (TCGA) GBM dataset. Material and Methods Total 399 patients from TCGA GBM data set were clustered into radiosensitive (RS) versus radioresistant (RR) groups using 30 genes alleged to radiosensitivity. According to median value of CD274 mRNA expression, patients were stratified as PD-L1-High versus PD-L1-low groups. Afterwards, the PD-L1-High-RR versus the others groups were composed, and survival outcomes were compared. Differentially expressed genes (DEGs) were identified, and enrichment analysis was performed as well. Differentially methylated regions (DMRs) were analyzed, and integrated into DEGs. Results Among 399 patients with GBM, we identified a group expressing a high level of PD-L1 and being clustered as a radioresistant (The PD-L1-High-RR) group as well. For patients treated with primary RT (N = 284), a Cox multivariate analysis demonstrated that membership in this group had detrimental effect for overall survival (HR = 1.70, 95% CI = 1.03 - 2.81, p =0.037). Differentially expressed genes in this group was highly enriched for immune response and mapped into activation of PI3K-AKT and MAPK signaling pathway. Integration of differentially expressed genes and methylated region found that BA1, which plays an important role in anti- angiogenesis, was epigenetically silenced in the PD-L1- High-RR. On the other hand, MAP3K8 involved T-cell receptor signaling pathway was upregulated epigenetically. Conclusion We validated the predictive value of a radiosensitivity gene signature and identified a subset, “PD-L1-High-RR group” which showed worse outcome compared to the rest of the groups. DEGs were associated with immune response and key oncogenic prosurvival signaling pathways and DMR showed that epigenetic regulating genes regulating T-cell receptor signaling and angiogenesis[Office1] . Taken together, The PD-L1-High- RR could be potentially benefit from anti-PD-1/PD-L1 blockades combined with antiangiogenic drug and RT using immune stimulating dose-fraction schedule. PO-0715 Validation of a prognostic score for patients with brain metastases based on extracranial factors. V. Lewitzki 1 , S. Heß 2 , C. Nieder 3 , M. Flentje 1 1 Julius-Maximilians University, Radiation Oncology, Würzburg, Germany 2 Julius-Maximilians University, Medical Faculty, Würzburg, Germany 3 Nordland Hospital, Department of Oncology and Palliative Medicine, Bodø, Norway Purpose or Objective The aim of our study was an external validation of a prognostic score predicting survival of patients with brain metastases suggested by Nieder et. al. . Material and Methods A retrospective analysis of 526 patients with brain metastases treated with any art of cranial radiotherapy was performed. Uni- and multivariate analyses included recursive partitioning analysis classes (RPA), diagnosis- specific graded prognostic assessment (DS-GPA) and score based on extracranial factors (EC-S, albumin, LDH and the number of extracranial organs involved). Results In our patient cohort (Table 1)the combination of extracranial factors correlated independently with overall survival in univariate and multivariate analysis also in comparison with RPA and DS-GPA. It was the most robust model predicting the patients with very poor survival. In the group of patients with combination of low albumin, elevated LDH and more than 1 extracranial