ESTRO 2021 Abstract Book

S920

ESTRO 2021

Conclusion HypoRT in locally advanced breast cancer patients shows acceptable acute skin toxicity, cosmetic outcome and relapse rates. It appears to be a reasonable approach in high volume centers to reduce the workload and improve patient compliance. However, longer follow-up is required for better assessment of late toxicity, relapse and survival outcomes. PO-1106 External beam APBI in early breast cancer: randomised prospective single institution study. P. Burkon 1,2 , I. Selingerova 3,4 , M. Slavik 1,5 , T. Kazda 1,2 , M. Vrzal 1 , P. Slampa 1,2 1 Masaryk Memorial Cancer Institute, Department of Radiation Oncology, Brno, Czech Republic; 2 Faculty of Medicine, Masaryk University, Department of Radiation Oncology, Brno, Czech Republic; 3 Masaryk Memorial Cancer Institute, Research Centre for Applied Molecular Oncology, Brno, Czech Republic; 4 Faculty of Medicine, Masaryk University, Department of Pharmacology, Brno, Czech Republic; 5 Faculty of Medicine, Masaryk University, Department of Radiation Oncology, Brno, Czech Republic Purpose or Objective The adjuvant radiotherapy (RT) of the early breast cancer as local treatment aims to eliminate the potential microscopic residual disease in the surgery bed. Based on published studies, accelerated partial breast irradiation (APBI) is recommended for strictly selected patients. Several techniques were shown to be appropriate, namely interstitial brachytherapy or external beam RT. Another possibility is stereotactic body radiotherapy (SBRT) which offers a more precise dose application associated with target volume reduction, which may lead to a reduction in toxicity and better cosmetic effect. The aim of this single-institution prospective randomized study was to compare the targeted APBI delivered by SBRT technique with the currently more commonly used accelerated whole breast irradiation in terms of feasibility, safety, tolerance, Early breast cancer patients after partial mastectomy were screened for eligibility. The inclusion criteria were age ˃ 50 years, no lobular histology, size ≤ 2 cm, margins ≥ 2 mm, L0, ER-positive, BRCA negative. Enrolled patients were equally randomized into two arms according to RT regiments – the SBRT surgery bed radiotherapy (5×6Gy) and accelerated whole breast irradiation with the boost (15×2,67Gy + 5×2Gy). These preliminary results of the ongoing study evaluated the first 57 from 84 planned patients. The follow-up evaluation was planned at the end of RT, one and three months after RT and then every three months. Quality of life was evaluated by the official Czech translation of EORTC QoL questionnaires. Cosmetics results and toxicity were evaluated using questionnaires, CTCAE criteria and photodocumentation of irradiated chest. Results The median age was 65 years. The tumors were grade 1 in 60% of patients, the median size of 9 mm and 70% were classified as invasive ductal carcinoma. Significant differences between groups in baseline characteristics were not observed. A total of 29 patients were enrolled in the SBRT group. All patients were evaluated one month after RT. A total of 40 and 33 patients had examinations 3 and 6 months after RT, respectively. Toxicity evaluation showed statistically significantly fewer acute adverse events in the SBRT group in terms of skin and cosmetic effects. Materials and Methods