ESTRO 2021 Abstract Book

S883

ESTRO 2021

1 Seoul National University College of Medicine, Department of Radiation Oncology, Seoul, Korea Republic of; 2 Ewha Womans University College of Medicine, Department of Radiation Oncology, Seoul, Korea Republic of; 3 Seoul National University College of Medicine, Department of Internal Medicine, Seoul, Korea Republic of; 4 Chung-Ang University College of Medicine, Department of Internal Medicine, Seoul, Korea Republic of; 5 Yonsei University College of Medicine, Department of Radiation Oncology, Seoul, Korea Republic of; 6 Sungkyunkwan University School of Medicine, Department of Radiation Oncology, Seoul, Korea Republic of; 7 Sungkyunkwan University School of Medicine, Department of Internal Medicine, Seoul, Korea Republic of; 8 National Cancer Center, Proton Therapy Center, Goyang, Korea Republic of; 9 The Catholic University of Korea, Department of Radiation Oncology, Seoul, Korea Republic of; 10 Seoul Metropolitan Government Seoul National University Boramae Medical Center, Department of Radiation Oncology, Seoul, Korea Republic of; 11 Chungnam National University College of Medicine, Department of Radiation Oncology, Daejeon, Korea Republic of; 12 Gyeongsang National University School of Medicine and Gyeongsang National University Changwon Hospital, Department of Radiation Oncology, Changwon, Korea Republic of; 13 Chonnam National University Hwasun Hospital, Department of Radiation Oncology, Hwasun, Korea Republic of; 14 Dongnam Institute of Radiological and Medical Sciences, Department of Radiation Oncology, Busan, Korea Republic of; 15 Korea University Medical College, Department of Radiation Oncology, Ansan, Korea Republic of; 16 Keimyung University Dongsan Medical Center, Department of Radiation Oncology, Anyang, Korea Republic of; 17 Wonju Severance Christian Hospital, Department of Radiation Oncology, Wonju, Korea Republic of; 18 Chosun University Medical School, Department of Radiation Oncology, Gwangju, Korea Republic of; 19 Seoul National University Bundang Hospital, Department of Radiation Oncology, Seongnam, Korea Republic of Purpose or Objective We analyzed the treatment outcome of breast cancer patients with brain metastases (BM) in Korea to identify the prognostic factors and the role of whole-brain radiotherapy (WBRT). Materials and Methods Seven hundred thirty patients of breast cancer with BM treated at 17 institutions in Korea from 2000 to 2014 were analyzed. The median follow-up duration was 12 months. The analysis consisted of three cohorts: in cohort A, a total of 730 patients were included; in cohort B, 538 patients with available follow-up imaging after initial brain-directed treatment; and in cohort C, 54 patients receiving salvage WBRT due to recurrent BM after initial brain-directed treatment. Overall survival (OS) was calculated from BM diagnosis in cohort A or from the last day of salvage WBRT in cohort C. Results Median OS of cohort A was 15 months. In multivariate analysis, histologic grade 3, extracranial metastasis, number of BM >4, hormone receptor (HR) or HER2 negativity, and shorter time interval to diagnosis of BM were associated with inferior OS. Among 538 patients in cohort B, 201 showed subsequent development of new BM at a median of 11 months after brain-directed treatment for the management of initial BM (at 1 year, HR+/HER2- 51.9%, HER2+ 44.0%, and TNBC 69.6%, respectively; p=0.008). Upfront WBRT reduced subsequent development of new BM, which showed the significant difference among molecular subtypes (HR+/HER2-, 42% reduction at 1 year, p<0.001; HER2+, 18.5%, p=0.004; TNBC, 16.9%, p=0.071). Multivariate analysis of cohort B showed that shorter time interval to BM, TNBC subtype, extracranial systemic disease, number of BM >4, and involvement of both tentoria increased subsequent development of new BM. Anti-HER2 therapy for HER2+ patients and upfront WBRT significantly reduced risk of new BM. In cohort C, upfront WBRT prolonged the salvage WBRT-free duration (median 6.9 vs. 8.7 months, p=0.058). Median OS was 6.8 months after salvage WBRT. Controlled primary tumor and systemic treatment after salvage WBRT showed better OS. Uncontrolled extracranial systemic disease and salvage WBRT due to local progression without distant intracranial failure showed worse OS. Conclusion The rates of new BM showed the significant differences among molecular subtypes. Upfront WBRT decreased subsequent development of new BM and this effect was dependent on the molecular subtype as well. Anti- HER2 therapy for HER2+ patients significantly decreased the subsequent development of new BM. On salvage WBRT setting, the patients having stable extracranial systemic disease and subsequent systemic therapy showed better OS. Purpose or Objective Several patients who receive radiosurgery for brain oligometastases or benign diseases live long enough to develop quality of life (QOL) issues due to impaired vision, memory or cosmesis (due to focal alopecia). Traditionally, neural optic structures are spared as critical structures but data on corneal, scalp and hippocampal doses are scarce. We attempted to evaluate doses to these structures in relation to tumor location within the brain. Primary objective was to study the planned dose to the delineated organs at risk (neural optic structures, cornea, hippocampus, scalp). Secondary objective was to correlate these with tumor location and doses estimated with thermoluminescent dosimetry (TLD) on scalp and cornea. Materials and Methods Axial computed tomography (CT) images of CIRS Atom phantom (900 Asbury Ave, Norfolk, Virginia, USA) were acquired from the CT simulator (Philips Big Bore 4DCT) at 1 mm slice thickness from vertex till carina, and co- registered with a normal volumetric contrast enhanced magnetic resonance study to help delineate optic structures, cornea, scalp and hippocampus, as well as lobar anatomy of brain. Multiple spherical target volumes of 1 cm axial diameter were delineated in each of the four cerebral lobes and in cerebellum, and PO-1064 Corneal and hippocampal dose in brain radiosurgery related with location: A phantom dosimetric study P. Vias 1 , S. Goyal 1 , R. Singh 1 , R. Madan 1 , V. Singla 1 1 Pgimer, Radiation Oncology, Chandigarh, India