ESTRO 2020 Abstract book

S45 ESTRO 2020

primarily from the SIB. Serious adverse events within the first year of follow-up were comparable in type and frequency (6.1%) to those following radiosurgery alone. The neurologic death rate after HA-WBRT+SIB was 27.4%. Conclusion HA-WBRT with SIB is a safe and effective therapeutic option for patients with multiple brain metastases and shows improved local tumor control of existing metastases and overall intracranial progression-free survival compared to WBRT alone. The potential to avoid neurocognitive side effects is being further explored in the multicenter phase II HIPPORAD trial. OC-0094 Patterns of Failure in Pediatric Medulloblastoma and Implications for Hippocampal Sparing S. Baliga 1 , B. Bajaj 2 , L. Vanbenthuysen 2 , J. Adams 2 , S. Gallotto 2 , E.A. Weyman 2 , M.P. Lawell 2 , N.J. Tarbell 2 , S.M. MacDonald 2 , T.I. Yock 2 1 The Ohio State University Comprehensive Cancer Center, Radiation Oncology, Columbus, USA ; 2 Massachusetts General Hospital/Harvard Medical School, Radiation Oncology, Boston, USA Purpose or Objective Hippocampal Sparing (HS) has been associated with preservation of memory in adult patients with brain metastases. This approach has not yet been prospectively evaluated in the pediatric population due to concerns of increased disease relapse in the peri-hippocampal region. We aim to determine the patterns of local, distant, and peri-hippocampal failures in a cohort of patients treated with proton beam therapy (PBT) for pediatric We performed a retrospective review and identified patients with histologically confirmed standard-risk (SR) or high-risk (HR) MB, who were treated with PBT at the Massachusetts General Hospital from January 2000- 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 medulloblastoma (MB). Material and Methods

executive function (p=0.01). High mean EQD 2 to the total brain (p=0.05) and thalamus (p=0.02) were associated with processing speed impairment. Conclusion The present study finds associations between impaired performance in verbal learning and memory, verbal fluency, executive function and processing speed, in patients who had received RT to left hippocampus and temporal lobe, left frontal lobe, thalamus and the total brain. Validation of these findings is being undertaken in a prospective study that will include pre-treatment neurocognitive assessment. OC-0093 Hippocampus-avoidance whole-brain irradiation with dose escalation on multiple brain metastases I. Popp 1 , S. Rau 1 , M. Hintz 1 , J. Schneider 1 , A. Bilger 1 , J.T. Fennell 1 , D.H. Heiland 2 , T. Rothe 1 , K. Egger 3 , C. Nieder 4,5 , H. Urbach 3 , A.L. Grosu 1,6 1 University Medical Center Freiburg, Department of Radiation Oncology, Freiburg im Breisgau, Germany ; 2 Medical Center - University of Freiburg, Department of Neurosurgery, Freiburg im Breisgau, Germany ; 3 Medical Center - University of Freiburg, Department of Neuroradiology, Freiburg im Breisgau, Germany ; 4 Nordland Hospital, Department of Oncology and Palliative Medicine, Bodø, Germany ; 5 Faculty of Health Sciences- University of Tromsø, Department of Clinical Medicine, Tromsø, Norway ; 6 German Cancer Consortium DKTK- German Cancer Research Center DKFZ- Heidelberg- Germany, Partner Site Freiburg, Freiburg im Breisgau, Germany Purpose or Objective Whole brain radiation therapy (WBRT) is the standard treatment for multiple brain metastases. However, WBRT ensures a relatively poor local tumor control and can lead to a significant neurocognitive decline. The aim of the current study was to investigate the efficacy of a hippocampus-avoidance WBRT with simultaneous integrated boost on the metastases (HA-WBRT+SIB) in patients with multiple cerebral metastases. Material and Methods Between May 2012 and December 2016, 66 patients were prospectively enrolled and treated with HA-WBRT+SIB analog to the constraints of the experimental arm of the HIPPORAD trial protocol (DRKS00004598). The HA- WBRT+SIB was performed with 30 Gy in 12 fractions and D98% in hippocampus ≤ 9 Gy, D2% ≤ 17 Gy. A SIB (51/42 Gy) was applied on metastases (2-16) and/or resection cavities (0-2). The 66 patients were further analyzed regarding survival, tumor control, occurrence of metastases in the HA-area, and toxicity. After 1:1 propensity score matching analysis, 62 HA-WBRT patients and 62 additional patients having received conventional whole-brain irradiation (WBRT, mostly 10x3 Gy) were selected and compared. Results Median follow-up time was 44.1 months (3.7 years) in the HA-WBRT+SIB group and was not reached in the WBRT group. The local tumor control of existing metastases was significantly higher in the HA-WBRT+SIB group (96% vs. 77% at 1 year, p=.004). At the last follow-up, from a total of 380 boosted lesions in the HA-WBRT+SIB cohort, 103 (27.6%) had a complete remission, 153 (40.3%) a partial remission, 47 (12.4%) were stable and 11 (2.9%) were progressive. The distant intracranial tumor control was significantly higher in the WBRT group (68% vs. 81% at 1 year, p=.016), corresponding to higher applied biologically effective doses (60.6 Gy vs. 42.1 Gy and 42.1 Gy vs. 37.5 Gy). Intracranial progression-free (12.8 vs. 5.8 months, p=.02) and overall survival (9 vs. 4.9 months, p=.0003) were significantly better in the HA-WBRT+SIB cohort. Five patients (7.6%) developed hippocampal or perihippocampal metastases after HA. The acute toxicity profile of HA-WBRT+SIB proved acceptable and derived

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