ESTRO 2020 Abstract Book

S336 ESTRO 2020

BCS+WBI after 10 years (OR=0.85; CI95%:0.59-1.22; p=0.369) and (OR=0.72; CI95%:0.38-1.36; p=0.305). In the network-analysis LR was significantly lower in the BCS+WBI group in comparison to the BCS+ET group (HR=0.62; CI95%:0.42-0.92; p=0.019).RR, RFI and DFS were not different between the two approaches. We also did not find any differences in OS (HR=1.00; CI95%:0.63-1.59; p=0.984) and BCSS (OR=1.18; CI95%:0.28-4.97; p=0.823). Further, we found a lower DMFI, a higher rate of CBC and a reduced MFI in the BCS+WBI-arm. Conclusion Evidence from direct and indirect comparison suggests that BCS+WBI without ET might be an equivalent de- escalation strategy to BCS+ET in low risk breast cancer. Adverse event rates and quality of life measures have to be further compared between these approaches. PH-0597 Radiation and/or endocrine therapy? Recurrence outcomes in low-risk breast cancer patients over 70 H. Dahn 1 , D. Wilke 1 , G. Walsh 2 , J. Pignol 1 1 Dalhousie University, Department of Radiation Oncology, Halifax, Canada ; 2 Dalhousie University, Department of Epidemiology, Halifax, Canada Purpose or Objective Women over 70 with early breast cancer treated with breast-conserving surgery are typically offered adjuvant endocrine therapy and radiation therapy. Prior studies have supported the omission of adjuvant radiation in this low-risk population. We sought to compare the effect of adjuvant treatment with endocrine therapy alone, radiation therapy alone or both versus no adjuvant treatment on local control and survival in a population of low-risk breast cancer patients over 70 years of age. Material and Methods Following local research ethics board approval, data was extracted on 1,363 low-risk breast cancer patients over the age of 70 treated with a breast-conserving surgery in Nova Scotia from 2003 until 2018. 460 patients met inclusion criteria of T1N0 invasive disease with negative margins and not treated with chemotherapy. The primary outcome was local recurrence-free survival at 5 and 10 years. Secondary outcomes included loco-regional recurrence-free survival, distant metastasis-free survival, disease-free survival and overall survival. Results Patients receiving no adjuvant therapy had worse local recurrence-free, loco-regional recurrence-free and disease-free survival than patients receiving at least one form of adjuvant therapy (p < 0.05). 5 year local- recurrence rates were 0.8% in patients receiving both endocrine and radiation therapy, 1.5% in those receiving radiation alone, 4.2% in those receiving endocrine therapy alone and 12% in those receiving no adjuvant therapy. There was no statistically significant difference for patients receiving at least one adjuvant therapy. On multivariate cox proportional hazard analysis, adjuvant endocrine therapy and adjuvant radiation therapy were statistically associated with local recurrence-free survival, while the tumor size, grade, LVI status and margin status were not. No significant difference in distant metastasis- free survival was seen between treatment groups.

Conclusion This study supports the equivalence of radiation therapy alone, adjuvant endocrine therapy alone and the combination of both in low-risk breast cancer patients over 70 treated with breast-conserving surgery. Receiving no adjuvant therapy is associated with poorer outcomes. As many of these patients are candidates for Accelerated Partial Breast Irradiation, the treatment decision could be between 5 years of endocrine therapy and 5 days of radiotherapy. When deciding about adjuvant therapy in this patient population, patients and clinicians should weigh toxicity and convenience of adjuvant endocrine therapy alone versus adjuvant radiation therapy alone, on a case-by-case basis, to guide treatment decisions. PH-0598 Normo versus hypofractionated whole breast irradiation: Are real life data what we expect? S. Guihard 1 , C. Petit 2 , J.B. Clavier 1 , L. Jung 1 , S. Servagi Vernat 3 , S. Bellefquih 3 , A. Ruffier 4 , G. Brusadin 2 , E. Remi 5 , S. Rivera 6 1 Paul Strauss, Radiotherapy, Strasbourg, France ; 2 Gustave Roussy, Radiotherapy, Villejuif, France ; 3 Jean Godinot, Radiotherapy, Reims, France ; 4 Institut interrégional de cancérologie- centre Jean-Bernard, Radiotherapy, Le Mans, France ; 5 Elekta, Radiotherapy, Paris, France ; 6 Institut Gustave Roussy, radiotherapy, Villejuif, France Purpose or Objective Although large volumes of information are entered on a daily basis into our electronic medical records, radiation oncology record and verify system and treatment planning systems the use of these Big Data is limited. To meet this goal we herein propose a multicenter data farming strategy structuring routine practice processes to improve availability and accuracy of key data elements for automated, electronic extraction to assess clinical outcomes in real life patients. The purpose of this study was to report real life rates and severities of acute radiation-related toxicities across centers in patients who received moderate hypofractionated (HF) versus normofractionated (NF) whole breast irradiation. Material and Methods We conducted a multicenter comprehensive systematic electronic data collection cohort study based on a standardized structured end of treatment evaluation and treatment characteristics form integrated in Mosaiq®. Three comprehensive cancer centers used a common evaluation form for breast cancer patients treated with