ESTRO 2020 Abstract Book

S43 ESTRO 2020

December 2016. Patients were treated with surgery, radiation (CSI and boost) and chemotherapy. Overall Survival (OS) and Event-free Survival (EFS) were evaluated using the Kaplan Meier method. Univariate and multivariate analysis were performed using a Cox proportional hazards model. The covariates included were age, histology, extent of resection, RT duration, and sex. Local, distant, and peri-hippocampal failures (defined as a failure within 15 mm of the hippocampus) were tabulated. Results There were a total of 144 patients including in the analysis, (SR: 102 (70.8%) HR: 42 (29.1%)). The median follow-up was 4.8 years (Range: 1-14.7). 90% of patients had a GTR/near GTR. The 5-year EFS was 80.4% for SR and 64.6% for HR patients. The 5-year OS was 85.3% for SR and 68.2% for HR patients. On univariate analysis, anaplastic histology (HR: 2.45, p=0.02) and subtotal resection (HR: 2.89, p=0.009) were associated with inferior EFS. Multivariate analysis confirmed that anaplastic histology (HR: 2.89, p=0.008) and STR (HR: 3.57, p=0.0037) remained significant for inferior EFS. 34 patients progressed, with a 5-year cumulative incidence of local and distant recurrence for the entire cohort of 16.0% and 13.3%, respectively. In 25 patients (74%), detailed imaging of the recurrence was available. No patient failed within the contoured hippocampus. The incidence of peri- hippocampal metastases in standard risk (n=13) and high risk (n=12) patients who failed was 7.7% in SR (1/13) and 8.8% in HR (1/12). Conclusion This is the first study to demonstrate the low incidence of peri-hippocampal failures in a proton-radiotherapy treated medulloblastoma cohort and provides the rationale to study hippocampal sparing in a prospective study of standard risk MB patients. This approach may improve neuro-cognitive outcomes in the standard risk MB cohort. OC-0095 Timing of immunotherapy and SRS – Does it affects the outcome of patients with brain metastases? E. Grøvik 1 , L. Nilsen 1 , I. Digernes 1 , C. Saxhaug 2 , Å. Helland 3 , K.D. Jacobsen 3 , O. Geier 1 , B. Breivik 4 , D.O. Sætre 5 , K. Emblem 1 1 Oslo University Hospital, Diagnostic Physics, Oslo, Norway ; 2 Oslo University Hospital, Radiology and Nuclear Medicine, Oslo, Norway ; 3 Oslo University Hospital, Oncology, Oslo, Norway ; 4 Hospital of Southern Norway, Radiology, Kristiansand, Norway ; 5 Østfold Hospital Trust- Klanes, Radiology, Kalens, Norway Purpose or Objective The introduction of immunotherapy (IMT) has led to a paradigm shift in the treatment of patients with metastatic cancer. Particular interest has been directed towards combining IMT with stereotactic radiosurgery (SRS) to improve treatment response. Lately, studies have indicated that the timing of IMT with SRS may be crucial for the patient outcome, suggesting that there is a window of opportunity to induce an optimal synergy between irradiation and immune agents 1,2 . To this end, this work investigates whether the timing of IMT with SRS affects the outcome of patients with brain metastases. Material and Methods Seventy-four patients from an on-going observational imaging study ( TREATMENT study; clinicaltrials.govidentifier: NCT03458455 ) with brain metastases from primary non-small cell lung cancer and malignant melanoma were included. Advanced study- MRIs were performed pre-SRS and longitudinally for up to 36 months. All patients received SRS (15-27Gy) to on average 1.9 metastases within one week of the pre-SRS MRI. The patients were classified into three treatment groups: 1) SRS only, 2), non-concurrent SRS and IMT, and 3), concurrent SRS and IMT (±4 weeks). The immunotherapy included anti-PD-1 (pembrolizumab,

nivolimumab or atezolizumab) or anti-CTLA-4 (ipilimumab), or a combination of the two. Patient demographics are shown in Table 1 . Overall survival was assessed from the time of the pre-SRS MRI.

Results Patients that received concurrent SRS and IMT showed an improved overall survival compared to patient treated with SRS only or non-concurrent SRS and IMT ( Figure 1 ). However, the differences found were not statistically significant (Group 1 vs. Group 3; P-value= 0.23) and (Group 2 vs. Group 3; P-value= 0.74).

Conclusion Our preliminary results indicate that combining SRS and IMT may result in an improved survival for patients with brain metastases compared to SRS treatment alone. Furthermore, our data show a trend towards an optimal treatment effect if SRS and IMT are given concurrently. This supports the hypothesis that there is a window of opportunity, and that the timing of IMT with SRS may affect the outcome of patients with brain metastases. References 1 Brooks, E.D. and J.Y. Chang, Time to abandon single-site irradiation for inducing abscopal effects. Nat Rev Clin