ESTRO 2023 - Abstract Book

S631

Monday 15 May 2023

ESTRO 2023

Conclusion Local recurrences were similar up to 3 years for both mastectomy and BCT, but continued to occur at a steady rate for BCT, independent of IM-MS RT. The risk of LR was lower with adjuvant systemic treatment. No effect of IM-MS RT on local recurrences was seen. Further analysis will be performed to understand these results in the context of disease stage and RT techniques. OC-0765 Pre-operative single-dose partial breast irradiation: five-year results of the ABLATIVE trial Y. Civil 1,2 , J. Vasmel 3 , R. Charaghvandi 4 , A. Houweling 3 , C. Vreuls 5 , P. van Diest 5 , A. Witkamp 6 , A. Doeksen 7 , T. van Dalen 8 , J. Felderhof 3 , I. van Dam 3 , B. Slotman 1 , A. Kirby 9 , H. Verkooijen 10 , D. van den Bongard 1,2 1 Amsterdam UMC, location VUmc, Radiation Oncology, Amsterdam, The Netherlands; 2 Cancer Center Amsterdam, Cancer Treatment and Quality of life, Amsterdam, The Netherlands; 3 UMC Utrecht, Radiation Oncology, Utrecht, The Netherlands; 4 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands; 5 UMC Utrecht, Pathology, Utrecht, The Netherlands; 6 UMC Utrecht, Surgery, Utrecht, The Netherlands; 7 St. Antonius Hospital, Surgery, Nieuwegein, The Netherlands; 8 Erasmus MC Cancer Institute, Surgery, Rotterdam, The Netherlands; 9 Royal Marsden NHS Foundation Trust/The Institute of Cancer Research, Radiation Oncology, Sutton, United Kingdom; 10 UMC Utrecht, Imaging Division, Utrecht, The Netherlands Purpose or Objective Preoperative partial breast irradiation (PBI) can result in an increased accuracy of target volume definition and decreased irradiated volumes compared with postoperative PBI. In the multicenter ABLATIVE trial (NCT02316561), 15/36 patients achieved pathologic complete response 6-8 months after preoperative single-dose PBI. We now present long-term outcomes of preoperative single-dose PBI and breast conserving surgery (BCS) including late toxicity, tumor recurrence, survival, cosmetic outcome and quality of life in low-risk breast cancer patients. Materials and Methods Between 2015 and 2018, 36 patients were treated with preoperative single-dose PBI followed by BCS after 6 (n=15) or 8 (n=21) months. The gross tumor volume (GTV), which is the breast tumor on MRI, and clinical target volume (CTV) (GTV+2cm) were expanded by a 3 mm planning target volume (PTV) margin. The prescribed dose was 20 Gy to PTV-GTV, and 15 Gy to PTV-CTV. Toxicity was scored at baseline and yearly visits until 5 years after PBI according to the Common Terminology Criteria for Adverse Events, and cosmetic outcome was assessed by patient and physician. Quality of life was evaluated yearly until 4 years after PBI using the European Organization for Research and Treatment of Cancer QLQ-C30 and BR23 questionnaires, and the Hospital Anxiety and Depression Scale. Changes in cosmetic outcome and quality of life scores from baseline over time were analyzed using linear mixed models. Results All women were aged ≥ 50 years and had invasive, unifocal, non-lobular breast cancer, estrogen receptor-positive, HER2- negative, and a tumor negative sentinel node. Median tumor size on MRI was 13 mm (range: 5-20 mm). After a median follow-up of 5.1 years (3.8–6.3 years), grade 1 breast fibrosis and breast discomfort/pain were present in 83% and 44% of the patients, respectively (table 1). Grade 2 breast fibrosis (3%) and fatigue (3%) at 3 years completely resolved at 5 years. Two (6%) patients developed ipsilateral breast events (DCIS (n=1) and invasive lobular carcinoma (n=1)) and two (6%) distant metastases. Five-year disease-free and overall survival rates were 89% and 94%, respectively. Shortly after BCS at 12 months, the proportion of patients (very) satisfied with the cosmetic results decreased from 89% (baseline) to 63%, before improving to 76% at 5 years (p=0.7) (fig. 1). Physicians rated the cosmetic result as excellent/good in 80% of the patients at 5 years versus 97% at baseline (p=0.4). The 4-year median QLQ-C30 and BR-23 scores were 93 (57-100) and 88 (68-99) respectively, with no change from baseline (p=1.0; p=0.5). Median anxiety and depression scores remained constant over 4 years (p=0.1; p=0.7).