ESTRO 2020 Abstract Book

S463 ESTRO 2020

3 Kasr Alaini- Cairo University, Clinical Oncology, Cairo, Egypt Purpose or Objective Routinely the hippocampus is not a contoured OAR when treating brain gliomas using 3D conformal radiotherapy (3DCRT) despite the expected radiation induced hippocampal damage. We proposed this dosimetric study to analyze the possibility of reducing the hippocampal dose using 3DCRT, rather than more advanced techniques like IMRT and VMAT proving feasibility in previous studies. Material and Methods This is a dosimetric study of 29 cerebral brain glioma patients who presented to the Radiation Oncology Department, National Cancer Institute, Cairo University from January 2018 to January 2019. Twenty three had high grade brain gliomas and 6 had low grade gliomas. For each patient, two plans were created. The first plan was done before contouring the hippocampus. The second plan was done after hippocampal contouring following the RTOG 0933 guidelines. The two plans were then compared in terms of dose reduction to the contralateral hippocampus.

3DCRT plans. Right: hippocampal Dmean. Left: hippocampal Dmax. Conventional 3DCRT: Blue, Hippocampal Avoiding 3DCRT: Red. Conclusion Contralateral hippocampal sparing is feasible by 3DCRT. Routine contouring of the contralateral hippocampus as an OAR is advised especially in low grade gliomas, which are expected to have a long survival.A clinical trial is being designed at our institute to evaluate the clinical impact. PO-0861 Survival outcomes after upfront stereotactic radiosurgery for brain metastases from breast cancer Y. Wang 1 , R. An 1 , C. Gao 2 , A. Singareeka Raghavendra 2 , D. Amaya 1 , N. Ibrahim 2 , J. Li 1 1 MD Anderson Cancer Center- University of Texas, Radiation Oncology, Houston, USA ; 2 MD Anderson Cancer Center- University of Texas, Breast Medical Oncology, Houston, USA Purpose or Objective As systemic therapy for metastatic breast cancer (BC) improves, effective treatment for central nervous system involvement has become a major concern, as 10% ‒ 30% of such patients develop brain metastases (BMs). The survival benefit from hormonal and targeted therapy urges to treat patients with BMs with minimal toxicity and less systemic interruption. Here we assessed survival outcomes in patients who received upfront stereotactic radiosurgery (SRS). Material and Methods We retrospectively reviewed 196 patients who received upfront SRS for BMs from metastatic BC at MD Anderson Cancer Center in August 2009 ‒ May 2018, of whom 71 had triple-negative (TN), 56 luminal A, 35 luminal B, 31 HER2, and 3 unknown molecular subtypes. Primary endpoints were overall survival (OS) from BM diagnosis and time to salvage (TTS) and were estimated by Kaplan-Meier survival analysis. Cox proportional hazard regression analysis was used to identify prognostic factors. Results Median age at BM diagnosis was 52 y (range 24 ‒ 82); median Karnofsky Performance Score (KPS) was 90 (range 60 ‒ 100); and median number of BMs treated was 2 (range 1 ‒ 18). At a median follow-up time of 13.1 months (mo) for all patients (range 1.47–111.3 mo; 21.9 mo for patients alive at last follow-up), the median OS time was 15.7 mo. Factors associated with OS on multivariate analysis (MVA) were subtype (11.8 mo for TN, 13.7 mo for luminal A, 35.7 mo for luminal B, and 28.3 mo for HER2, p =0.003), KPS (1.5 mo for 60, 5.97 mo for 70, 10.0 mo for 80, 18.1 mo for 90, and 20.9 mo for 100, p =0.003) and receipt of salvage therapy ( p =0.008). Of the 102 patients (52%) who received salvage therapy after initial SRS, 61 received salvage whole-brain radiation therapy (WBRT) and 41 received salvage SRS. The median TTS was 6.7 mo (range 0.6 ‒ 63 mo). The 12-month salvage rate was 18.8% for WBRT and 24.5% for SRS. Patients who received salvage SRS had better OS than those who received salvage WBRT or SRS+WBRT (47.6 mo for salvage SRS, 15.1 mo for salvage WBRT, and 28.8 mo for SRS+WBRT, p <0.001). On MVA, OS was worse for those received salvage WBRT vs. salvage SRS (hazard ratio 4.6, p =0.06). Number of BMs treated by initial SRS did not affect OS (17.1 mo for <4 [n=151 patients] vs. 12.1 mo for >/= 4 [n=45 patients], p =0.4). Receipt of hormonal or HER2 therapy after BM diagnosis was associated with improved OS on univariate but not MVA. Conclusion Patients who received upfront SRS for BMs from BC had median OS of 15.7 mo and TTS of 6.7 mo. Molecular subtypes luminal B and HER2, good KPS, and possibly receipt of targeted or hormonal therapy predicted better OS. Number of BMs treated by upfront SRS was not associated with OS. Salvage SRS is associated with better OS compared to WBRT and this may reflect patient

Figure 1: Axial views of isodose coverage of conventional 3DCRT plan vs. hippocampal avoiding 3DCRT plan for one patient. Hippocampus: Orange, Hippocampal Avoidance Zone: White, PTV: Green. Left: Isodose coverage of conventional 3DCRT (RT Hippocampus D mean 29.33Gy, D max 33.76Gy). Right: Isodose coverage of hippocampal avoiding 3DCRT (RT Hippocampus D mean 18.72Gy, D max 23.31Gy). Results The hippocampal Dmean was reduced from 21.93Gy to 13.83Gy, with a 32.1% reduction (p value <0.0001). The hippocampal Dmax was reduced from 35.04Gy to 23.58Gy, with a 30.4% reduction (p value <0.0001). By further analysis a higher reduction was achieved in the low grade glioma subgroup with a 48.15% and 45.4% reduction of the Dmean and Dmax, respectively. PTV to hippocampus distance was not of a statistical significance in hippocampal Dmean reduction; however, there was a significant Dmax reduction with distances of ≥ 8 mm. PTV’s volume and tumor site had no significance on reduction feasibility.

Figure 2: Box plot graphs of hippocampal Dmean and Dmax in conventional 3DCRT plans vs. hippocampal avoiding