How Do the ASTRO Consensus Statement Guidelines for the Application of Accelerated Partial Breast Irradiation Fit Intraoperative Radiotherapy? A Retrospective Analysis of Patients Treated at the European Institute of Oncology

Purpose: To verify how the classification according to the American Society for Therapeutic Radiation Oncology (ASTRO) consensus statement (CS) for the application of accelerated partial breast irradiation (APBI) fits patients treated with intraoperative radiotherapy with electrons (ELIOT) at a single institution. Methods and Materials: The study included 1,822 patients treated with ELIOT as the sole radiation modality outside of a clinical trial at the European Institute of Oncology after breast-conserving surgery for invasive breast cancer, who were classified into CS groups of suitable, cautionary, and unsuitable. The outcome in terms of ipsilateral breast recurrence, regional node relapse, distant metastases, progression free-survival, cause-specific survival, and overall survival were assessed. Results: All the 1,822 cases except for 25 could be classified according to ASTRO CS: 294 patients met the criteria for inclusion into the suitable group, 691 patients into the cautionary group, and 812 patients into the unsuitable group. The 5-year rate of ipsilateral breast recurrence for suitable, cautionary, and unsuitable groups were 1.5%, 4.4%, and 8.8%, respectively (p = 0.0003). Whereas the regional node relapse showed no difference, the rate of distant metastases was significantly different in the unsuitable group compared with the suitable and cautionary groups, having a significant impact on survival. Conclusion: In the context of patients treated with ELIOT, the ASTRO guidelines identify well the groups for whom APBI might be considered as an effective alternative to whole breast radiotherapy and also identify groups for whom APBI is not indicated.