E80: The Impact of Postmastectomy Radiation Therapy on Direct-to-Implant Reconstruction

Introduction: With advancement of surgical technique and acellular dermal matrices, there has been a shift from two-stage tissue expander to implant reconstruction to direct to implant reconstruction (DTI) following mastectomy. We investigated the impact of post mastectomy, radiation therapy (PMRT) clinical outcomes in patients with DTI.

Methods: We conducted a retrospective analysis of consecutively treated patients with non-metastatic breast cancer, who received a mastectomy with DTI with or without PMRT from January 2019 to July 2023 at a single institution. Wilcoxon Ranked-Sum and Fisher's Exact Test's were used to compare outcomes between patient cohorts. Univariate (UVA) and multivariable (MVA) analyses were conducted to identify potential predictors (including age, BMI, smoking status, hypertension, diabetes, implant size, receipt of chemotherapy, endocrine therapy, and radiation therapy) of clinical outcomes.

Results: We identified 101 patients who underwent a mastectomy with pre-pectoral DTI, including coverage with an acellular dermal matrix (87%). 20 patients (20%) receive PMRT to the chest wall with (85%) or without (15%) regional nodal radiation. Conventionally (75%) or moderately hypofractionated (25%) PMRT was delivered with photons (70%), or protons (30%). A boost to the surgical scar/chest wall was administered in 50% of patients. Bolus was utilized and 57% of photon treatments and in no proton treatments. Chemotherapy was received by 30% of patients who did not receive PMRT and by 70% of patients who received PMRT (P=0.002). Median follow up with 15 months (8, 28 months). Compared to patients who did not receive PMRT, patient who receive PMRT showed similar rates of unplanned reconstructive surgery (38% versus 15%, P=0.064) and similar rates of implant failure (4.9% versus 5%, p >0.9). UVA, increasing age and implant volume predicted implant failure, and this correlation remained significant on MVA (OR=1.22,[1.06, 1.49](P=0.014) and OR=1.01,[1.002,1.02](P =0.038), respectively).

Conclusions: In this cohort, increasing age and implant size predicted implant failure. Receipt of PMRT was not associated with higher rates of unplanned reconstructive surgery or implant failure.