摘要：Abstract Background and purpose Patients with breast cancer receiving mastectomy in our institution are offered immediate breast reconstruction (IBR). IBR may have an impact on the optimisation of radiation therapy (RT). Therefore, we aimed to evaluate the clinical target volume (CTV) dose coverage when disregarding the dose received by the breast implant in women treated for breast cancer. Furthermore, to investigate the safety of immediate breast reconstruction (IBR) with an implant (IBR+) in terms of recurrence and survival compared to patients without an implant (IBR−). Patients and methods This matched-cohort included 128 patients with IBR+ and 252 IBR− patients (controls). The potential confounding effects of tumour stage and treatment were controlled for. For IBR+ patients, the implant volume was excluded from the CTV in the RT planning images, and the RT target coverage (V95%: CTV covered by ≥the 95% isodose) was compared between the IBR+ and IBR− groups. Results A limited under dosage was observed in patients without lymph-node irradiation; the V95% mean values for the CTV subtracting the implant were 84% and 92%, for IBR+ and IBR− groups, respectively. Median follow-up duration was 5.8 years (0.1–7.5 years). In comparing IBR+ and IBR− groups, no statistically significant differences were found in the incidence of recurrence rate ratios or recurrence free survival (log-rank p = 0.142), overall survival (log-rank p = 0.096), or breast cancer specific survival (log-rank p = 0.147). Conclusions Post-mastectomy radiation therapy and implant-based reconstruction lead to minor under dosage of the target, due to the projection of the subcutaneous tissue in the presence of the implant. However, recurrence and survival rates were equally distributed among IBR+ and IBR− patients indicating that the overall treatment protocol used in our institution is safe.