Abstract Book

ESTRO 37

S371

calculated using the Kaplan-Meier method and cumulative incidence with competing risk for death, respectively. Multivariable Cox models were applied to adjust for confounders. Results A total of 189 pts with 329 BM treated with SRS had post- treatment NLR that could be calculated: 138 (73.0%) pts with 234 (71.1%) BM had a NLR ≤6. The most prevalent histologies were lung (37.6%), melanoma (27.3%), breast (19.0%), other (7.3%), renal (6.8%), and GI (2.0%). Baseline pt characteristics (including histology, active systemic disease, extracranial metastases [ECM], use of any systemic therapy [ST], ST pre- and post-SRS, and type of ST [chemo, targeted, immune, or hormone therapy] pre- and post-SRS) were well balanced amongst the cohorts, with the only statistical difference being lower rate of ECOG performance status 0 in the NLR >6 (33.3% vs. 44.2%, p=0.038) group. No differences were seen in treatment (including dose, number of fractions, margin size, GTV, PTV) characteristics amongst the cohorts. The median time to death or last follow-up was 17.9 vs. 12.9 months for NLR ≤6 vs. >6, respectively. A statistically significant (p=0.0277) survival advantage was seen in patients with a NLR ≤6. OS estimates at 6, 12, and 24 months were 94.9% vs. 90.1%, 72.9% vs. 59.9%, and 43.9% vs. 24.6%, amongst patients with NLR ≤6 vs. >6, respectively. Post-SRS NLR, graded prognostic assessment, and presence of ECM were significant on univariate analysis. Multivariable analysis confirmed that post-SRS NLR >6 (Hazard Ratio [HR]: 1.56; 95% confidence interval [CI] 1.07-2.27, p=0.022) and ECM (HR: 1.76; 95% CI 1.15-2.68, p=0.009) were significant for worse survival. No statistically significant differences were noted in local failure (1-yr estimates: 10.5% vs. 12.0%) or radiation necrosis (1-yr estimates: 14.3% vs. 16.4%) amongst patients with NLR ≤6 vs. >6, respectively. Conclusion Post-treatment NLR, a potential marker for post-SRS inflammatory response, is inversely associated with OS for BM treated with SRS. If prospectively validated, NLR could be deployed as a stratification and/or eligibility variable in clinical research and a predictive biomarker for more aggressive subsequent treatments. PO-0726 Long term follow up of patients with meningioma after stereotactic radiation therapy (SRT) J.T. Fennell 1 , S.S. Walter 2 , O. Oehlke 1 , A. Bilger 1 , O. Schnell 3 , A.L. Grosu 1 1 University Medical Center Freiburg, Department of Radiation Oncology, Freiburg, Germany 2 University Hospital Tuebingen, Department for Diagnostic and Interventional Radiology, Tuebingen, Germany 3 University Medical Center Freiburg, Department of Neurosurgery, Freiburg, Germany Purpose or Objective Meningiomas are the most common primary brain tumor in adulthood. While surgery remains the first line therapy in most cases, SRT has become established as adjuvant treatment after subtotal resection, as primary therapy of meningiomas located close to organs of risk and in cases of recurrence. Since most meningiomas are low grade, a long follow up after SRT is needed to evaluate treatment response. The following are the long term results after SRT of meningiomas in a single institution. Material and Methods In this retrospective analysis we evaluated local tumor control (LTC), progression free survival (PFS) and overall survival (OS) of 266 patients, who were treated for meningioma with either stereotactic radiosurgery (SRS) or stereotactic fractionated radiotherapy (SFRT) in a single center between 1990 and 2013. To assess side effects the

Common Terminology Criteria for Adverse Events (CTCAE) was used. Results The median follow-up was 50.5 months. In 45.5 % (121/266) of cases, there was no histopathological WHO grading available (NGA), 41.4% (110/266) of cases were WHO°I, 8.6 % (23/266) WHO°II and 4.5% (12/266) WHO° III meningiomas. 71.4 % of patients previously received surgery. Meningiomas with NGA or WHO°I had a LCT rate of 95.5.% after 3 years (3y), 89.8% after 5 years (5y) and 80.9% after 10 years (10y), when treated with SRS. After SFRT, LCT was 97.8% (3y), 92.1% (5y) and 86.2% (10y). PFS was 92.8% (3y), 86% (5y) and 77.5 % (10y) after SRS and 94.2% (3y), 86% (5y) and 76.8% (10y) after SFRT. OS was 93.8% (3y), 91.1% (5y) and 89% (10y) after SRS and 96.3% (3y), 93.4% (5y) and 85.4% (10y) after SFRT. Only 3 patients with WHO°II/III meningiomas were treated with SRS, thus the following results are only for SFRT. LCT was 66.4% (3y) and 59% (5y, 10y). PFS was 55.5% (3y) and 42.8% (5y, 10y). OS was 63.7% (3y) and 55.2% (5y, 10y). The most common CTCAE Grad III toxicities were impaired vision (1.5%) and double vision (0.8%), while the most common CTCAE grade IV toxicities were brain edema (3%), followed by impaired vision (1.1%) and radiodermatitis (0.8%). Before SRT patients presented with visual symptoms (54.9%), dizziness (21.4%) and affection of the trigeminal nerve (21.4%). Over time, SRT improved impaired vision in 20.8%, double vision in 35.4%, impaired facial field in 13.2%, dizziness in 24.6% and symptoms of the trigeminal nerve in 28.1% of cases. SRT aggravated those symptoms in 14.3%, 4.9%, 0%, 14% and 7% of cases, respectively, and they newly occurred after SRT in 4.2%, 1.1%, 0%, 9% and 1% of cases, respectively. Conclusion SRT poses a good treatment option for patients with meningioma with good LCT, PFS and OS especially in cases of low histopathological grading. Long term, the rate of improved neurological symptoms is higher than the risk of neurological side effects. PO-0727 Disease Outcomes after GK-SRS for Brain Metastases:a prospective institutional registry analysis F. Moraes 1 , J. Winter 2 , A. Dasgupta 1 , H. Raziee 1 , C. Coolens 2 , G. Zadeh 3 , P. Kongkham 3 , M. Bernstein 3 , T. Conrad 1 , N. Laperriere 1 , B. Millar 1 , A. Berlin 1 , D. Shultz 1 1 Princess Margaret Cancer Centre, Radiation Medicine Program, Toronto, Canada 2 Princess Margaret Cancer Centre, Medical Physics, Toronto, Canada 3 Princess Margaret Cancer Centre, Neurosurgery, Toronto, Canada Purpose or Objective Marginal tumor dose prescription (DP) from radiosurgery (SRS) for brain metastasis (BM) affects rates of local failure (LF) and symptomatic radionecrosis (RN). In our BM program, we treat lesions adjacent to eloquent structures (e.g. motor cortex) with a smaller DP to reduce the likelihood of adverse side effects. We aimed to determine the effect of DP (15 Gy vs. ≥ 20Gy) on LF and RN for small- to medium-sized BM (≤ 2 cm). Material and Methods A prospective registry of BM patients treated with gamma knife SRS between January 2008 and September 2016 was reviewed to determine per lesion rates of LF and RN. Each tumor was followed from the date of SRS until LF or RN or at last MRI follow-up. Defined criteria were used to differentiate LF from RN, including pathology, when available. Whole brain irradiation (WBI) was a censoring event. Cumulative Incidence (CI) of LF and RN were estimated using a competitive risks analysis with death as