ESTRO 2021 Abstract Book

S46

ESTRO 2021

Department of Radiation Oncology, Ghent, Belgium; 8 University of Toronto, Radiation Oncology Program, Toronto, Canada

Purpose or Objective Hypofractionated radiotherapy (HR) for early breast cancer has been found to be equivalent to conventional fractionation (CF) in several large studies. More recently, accelerated HF regimens and HF in more advanced disease has been evaluated and adopted. Using data from the European Society of Radiation Oncology’s (ESTRO) Global Impact of Radiotherapy in Oncology (GIRO) initiative survey on HF, this study aims to identify patterns, facilitators and barriers to uptake of breast cancer HF across World Bank income groups. Materials and Methods The ESTRO-GIRO initiative administered an anonymous, electronic survey to radiation oncologists from January 2018 to January 2019. Details on physician demographics, clinical practice, preferred HF regimen for specific breast cancer clinical scenarios (curative and palliative), justifications and barriers for HF practices were collected. Curative scenarios included: node-negative (N0) following breast-conserving surgery (BCS) and mastectomy, and node-positive (N+) following BCS and mastectomy. The palliative scenario evaluated HF for symptom control. Factors associated with HF were assessed using multivariate logistic regression models. Results A total of 1,434 physicians responded to the breast survey scenarios, with 1251 (87%) from high-income (HICs) and upper middle-income countries (UMICs) and 183 (13%) from low and low middle-income countries (LMICs). The most common HF fraction size, reported by 30% of respondents, was between 2.5 and 2.9 Gy delivered in a total of 15 fractions for curative indications (2.1-4Gy); only 1% of respondents reported using a 5-fraction regimen. For palliative indications, the most common HF fraction size, used by 23% of respondents, was between 3Gy and 3.5Gy in 10 fractions (2.1-6Gy). In N0 disease following BCS, there was no significant difference in use of hypofractionation in LMICs compared to HICs and UMICs. Respondents in Africa were less likely to hypofractionate compared to Europe (OR = 0.29, CI 0.12,0.69; p=0.006) and those using Cobalt-60 were less likely to hypofractionate than those with linear accelerators (OR = 0.55, CI 0.37,0.84; p=0.005). In the other curative scenarios, those in LMICs were more than twice as likely to hypofractionate compared to those in HICs and UMICs. There were no differences in use of HF across income groups for palliative symptom control. Published evidence was the most cited justification for HF (89%) across income groups. Lack of advanced technology was cited as a barrier by 14% in LMICs, compared to 5% in HICs and UMICs. Conclusion Apart from N0 disease following BCS, patterns of HF for breast cancer varied across income groups for curative indications, with minimal uptake of accelerated regimens. Targeted interventions are needed to address barriers to HF and support evidence-based utilization. OC-0073 Reirradiation of brain metastases with SRS after local or marginal recurrence from prior SRS R. Kowalchuk 1 , A. Niranjan 2 , C. Lee 3 , H. Yang 3 , R. Liscak 4 , K. Guseynova 4 , M. Tripathi 5 , N. Kumar 6 , S. Peker 7 , Y. Samanci 7 , J. Hess 8 , V. Chang 8 , C. Iorio-Morin 9 , D. Mathieu 9 , S. Pikis 10 , Z. Wei 2 , L. Lunsford 2 , D. Trifiletti 11 , J. Sheehan 10 1 Mayo Clinic, Radiation Oncology, Rochester, USA; 2 University of Pittsburgh, Neurological Surgery, Pittsburgh, USA; 3 Neurological Institute, Taipei Veteran General Hospital, Neurosurgery, Taipei, Taiwan; 4 Na Homolce Hospital, Stereotactic and radiation neurosurgery, Prague, Czech Republic; 5 Postgraduate Institute of Medical Education and Research, Neurosurgery, Chandigarh, India; 6 Postgraduate Institute of Medical Education and Research, Radiotherapy, Chandigarh, India; 7 Koc University School of Medicine, Neurosurgery, Istanbul, Turkey; 8 Yale, Neurosurgery, New Haven, USA; 9 Université de Sherbrooke, Neurosurgery, Quebec, Canada; 10 University of Virginia, Neurosurgery, Charlottesville, USA; 11 Mayo Clinic, Radiation Oncology, Jacksonville, USA Purpose or Objective Brain metastases represent a major indication for stereotactic radiosurgery (SRS), and while there is evidence demonstrating efficacy of SRS after whole brain radiotherapy (WBRT), there is a paucity of literature regarding its role after local or marginal recurrence of a brain metastasis previously treated with SRS. We report local tumor control (LC) and radiation necrosis (RN) rates after the second SRS procedure, and we identify predictors of RN and symptomatic RN (SRN). Materials and Methods An international, multi-institutional study was performed under the auspices of the International Radiosurgery Research Foundation. We included patients with biopsy-proven non-small cell lung cancer with at least one brain metastasis status-post treatment with SRS. Repeat SRS (SRS2) was performed from 2015 through 2019 after local or marginal recurrence following initial SRS (SRS1). Patients receiving SRS after only WBRT or those treated with preoperative SRS were excluded. The primary endpoints were LC by RANO criteria, RN, and SRN. Results A set of 154 lesions treated in 124 unique patients was assembled from 8 institutions, with 134 treatments included in the final outcomes analysis. 41 treatments involved prior immunotherapy use, and SRS1 occurred a median 12 months prior to SRS2. SRS1 involved delivery of a median 18 Gy (10-27) margin dose to the 55% (35- 96) isodose line, with a maximum dose of 32.2 Gy (0.7-67.5) and a V12Gy of 3.94 cc (0.05-110.37). SRS2 had a median 18 Gy (10.5-30) margin dose to the 50% (19-96) isodose line, with a maximum dose of 32 Gy (16.2-85) and a V12 of 3.31 cc (0.02-71.3). At a median 15 months of follow-up after SRS2, 23.9% of lesions had progressed, with 1-year and 2-year LC of 78.9% and 71.6%. LC was reduced with tumor volume > 1 cc on SRS2 (p=0.01). RN occurred after 28 (20.9%) treatments, with 10 (7.5%) cases of SRN. Increasing values of SRS1 maximum dose, SRS2 maximum dose, SRS1 V12, and SRS2 V12 correlated with increasing rates of SRN and RN. Proffered papers: Proffered papers 4: CNS