Locoregional control and patterns of locoregional failure in women with breast cancer treated by highly conformal electron beam irradiation

Purpose. - The purpose of this study was to evaluate locoregional control and describe the patterns of locoregional failure in women with breast cancer irradiated by a previously described post-mastectomy highly conformal electron beam radiotherapy technique. Material and methods. - We included all women irradiated by post-mastectomy highly conformal electron beam radiotherapy technique for non-metastatic breast cancer between 2007 and 2011 in our department. All cases of bilateral breast cancer were excluded. All patients who experienced locoregional recurrence have been studied. Mapping patterns of regional recurrences was also performed and compared with the European Society for Radiotherapy and Oncology (ESTRO) and Radiotherapy Oncology Group (RTOG) guidelines of volume definition and delineation guidelines. Results. - With a median follow-up of 64 months (range: 6-102 months), 5-year locoregional recurrence free and overall survival probabilities were 90 %(95 % confidence interval [95 %CI]: 88.1-92.4) and 90.9 % (95 %CI: 88.9-93), respectively. Among the 796 patients included in the study, 23 patients (2.9 %) presented locoregional recurrences of them only 13 (1.6%) were presented with local recurrence. The majority of them presented aggressive biological features with grade Ill tumours in 17 patients (74 %) with high mitotic index in 16 cases (70 %) and triple negative tumours in 12 (52 %). Lymphovascular invasion was observed in 11 cases (48 %). In 14 cases the locoregional recurrences were diagnosed at the same time as the metastatic disease whereas 4 patients presented distant metastases secondarily. Locoregional recurrences occurred in 11 cases "in field" although adequate doses and volumes were used and in 12 cases "outfield", out of irradiated volume. Local recurrences occurred in 13 patients with 12 recurrences within the irradiated volumes. Regional recurrences occurred in 13 patients with 15 lymph nodes metastases identified. Four nodal recurrences occurred outside the ESTRO clinical target volume and within the RTOG clinical target volume and two occurred outside both RTOG and ESTRO clinical target volumes. Conclusion. - In presented series, the local recurrence resulted mostly from of biologic radio resistance whereas regional recurrences were caused by geographical miss. A number of nodal recurrences could occur outside the target volumes defined by ESTRO and RTOG. (C) 2018 Published by Elsevier Masson SAS on behalf of Societe frangaise de radiotherapie oncologique (SFRO).