TEN-YEAR OUTCOMES AFTER BREAST-CONSERVING SURGERY WITH INTRAOPERATIVE RADIOTHERAPY FOR BREAST CANCER

The purpose of the study was to analyze the 10-year outcomes after breast-conserving surgery with electronbeam intraoperative radiation therapy (IORT) followed by external beam radiotherapy (EBRT) in patients with breast cancer. Material and methods. The study included 905 patients with stage T1–2N0–1M0 breast cancer, who underwent breast-conserving surgery. Group I consisted of 746 patients who received IORT at a single dose of 10 Gy, biologically equivalent to 24.8 in standard fractionation, followed by EBRT at a total dose of 46 ± 8.1 Gy. A combined IORT and EBRT photon-equivalent dose delivered to the tumor bed was 60 Gy. Group II (control group) comprised 159 who received EBRT at a total dose of 40–44 Gy delivered to the remaining breast tissue and electron therapy delivered to the area of postoperative scar (a single 3–4 Gy fraction, 3 days per week, to the total photon-equivalent dose of 15-18 Gy). The combined photon-equivalent dose was 58 Gy. Results. According to RTOG/EORTC toxicity criteria, grade 1 radiation-induced damage was observed in 413 (55.3 %) patients of Group I and in 71 (44.6 %) patients of Group II (р=0.2); grade 2 radiation-induced damage in 76 (10.1%) and 43 (27 %) patients (p=0.0002) and grade 3 in 18 (2.4 %) and 9 (5.7 %) patients, respectively (р=0.1). Late radiation-induced injuries (grade I and 2) were mostly observed in the control group. Local recurrence was diagnosed in 11 (1.47 %) patients of Group I and in 14 (8.8 %) patients of Group II. The 10-year disease-free survival rates were 97.3 ± 1.08 % and 88.96 ± 2.8 % in Group I and Group II patients, respectively (р