Clinical outcomes and toxicity of electron-based intraoperative radiotherapy for partial breast irradiation: a single-institution experience

Purpose: Partial breast irradiation (PBI) using intraoperative electron radiotherapy (IOeRT) represents an attractive alternative to whole-breast irradiation in carefully selected patients with early breast cancer. Materials and Methods: Eighty-nine patients treated with single-dose 20Gy IOeRT between December 2012 and October 2022 were retrospectively analyzed.Most patients had early-stage disease, predominantly T1 tumors (84.3%), without adverse pathological features such as G3 grading or human epidermal growth factor receptor 2 overexpression.Follow-up examinations were conducted postoperatively, at 6 weeks, and every 6 months thereafter.Outcomes included overall survival (OS), progression-free survival (PFS), and in-breast progression-free survival, assessed using Kaplan-Meier analysis.The impact of clinical and treatment-related factors (e.g., age, tumor stage, grading, receptor status, endocrine therapy, electron energy, tumor localization, and re-resection) on survival and adverse events (AEs) was evaluated using log-rank tests and bivariate analyses.Results: After a median follow-up of 33 months, OS and PFS at 60 months were 98.8% and 82.9%, respectively.Six patients developed disease progression; only one experienced local recurrence after 56 months (ipsilateral breast tumor recurrence 1.1%), while the remaining cases were distant metastases.No ≥grade 3 toxicity occurred.Acute AEs included radiogenic dermatitis (15.7%) and seroma formation (8.9%), whereas fatigue was the most common late AE (5.6%).No significant associations between evaluated factors and survival outcomes or AEs were observed.Notably, two progression events occurred in patients with T2 or node-positive disease.Conclusion: IOeRT-PBI demonstrated encouraging short-term local control and low toxicity in this real-world low-risk cohort.While results are consistent with existing intraoperative radiotherapy data, longer follow-up and prospective validation are warranted before broader clinical implementation.