The patterns and spatial locations of local recurrence in breast cancer with implant-based reconstruction after mastectomy

•We analyzed the pattern of local recurrence in patient who had undergone mastectomy with implant reconstruction.•ESTRO ACROP consensus guideline for PMRT after immediate implant –based reconstruction encompassed most local recurrences.•The ESTRO-target volume covered 93.0% in patients with subpectoral implant, and 100% in patients with prepectoral implant.•Our results support ESTRO ACROP consensus guideline. The European Society for Radiotherapy and Oncology (ESTRO) recently defined delineation guidelines for the clinical target volume for postmastectomy radiation therapy (PMRT) after immediate implant-based reconstruction for early-stage breast cancer. We analyzed the three-dimensional location and pattern of local recurrence in accordance with the reconstruction type and ESTRO-target volume. This retrospective study involved patients who had undergone mastectomy with implant reconstruction between 2010 and 2019 and who had local recurrence as the first event. For mapping analysis, one subpectoral and one prepectoral implant patient were selected. All recurrence lesions were contoured and mapped in a representative case. A total of 1327 patients with breast cancer who underwent mastectomy and implant-based breast reconstruction were identified; 51 were enrolled with a total of 65 lesions. In subpectoral implant patients, 93% of recurrences were located in the ESTRO-target volume. No recurrence occurred in the implant pocket, but 7% of the recurrent tumors developed in the pectoralis major and deep thoracic muscle. In prepectoral implant patients, all recurrent tumors occurred within the ESTRO-target volume. The ESTRO-target volume in PMRT after reconstruction encompassed most local recurrences in patients who underwent mastectomy with immediate implant reconstruction. Our results support the application of the ESTRO Advisory Committee for Radiation Oncology Practice consensus guideline for target volume of PMRT after immediate implant-based reconstruction for early-stage breast cancer.