Impact of Pre-pectoral Implant Placement and Radiation Modalities (Protons/Photons) in Mastectomy Patients undergoing Immediate Direct-to-Implant Breast Reconstruction.

Background: For breast cancer patients receiving mastectomy with direct-to-implant (DTI) immediate breast reconstruction, placing the implant in the pre-pectoral or subpectoral plane remains debatable; especially in settings of postmastectomy radiotherapy (PMRT).

Materials/methods: We reviewed 3,039 patients who underwent mastectomy and reconstruction at our institution between 2005 and 2020. Patients receiving DTI with and without PMRT were included. PMRT was delivered either with photon (3D-conformal or VMAT) or proton therapy mainly with pencil beam scanning. All patients received conventional fractionation (50-50.4Gy in 25-28fractions). Primary endpoints were reconstruction complications defined as infection/necrosis requiring debridement; capsular-contracture requiring capsulotomy; absolute-reconstruction-failure entailing permanent removal of the implant without replacement (i.e: no salvage reconstruction) and overall-reconstruction-failure (removal of implant for any complication with and without salvage reconstruction). Different subgroups analyses were done.

Results: 815 patients met inclusion criteria, with an overall median follow-up of 6.2 years. We found that there is no significant difference between pre-pectoral vs sub-pectoral for infection/necrosis (OR:1.5, p=0.3); capsular-contracture (OR:0.97, p=0.9); absolute-reconstruction-failure (OR:1.9, p=0.12) and overall-reconstruction-failure (OR:1.2, p=0.5). Findings were confirmed using both logistic regression, time-to-event analysis and multivariable analyses for the entire cohort and subgroups with and without PMRT. There was no significant difference between Protons and Photons in terms of infection/necrosis (OR:1.6, p=0.4) and absolute-reconstruction-failure (OR: 1.2, p=0.7), but significantly higher risks for capsular-contracture with protons (OR:4.4, p<0.001) and overall-reconstruction-failure when compared to photon(OR:2.0, p=0.05). We did not find significant correlation pattern between different dosimetry factors (Dmean, Dmax, volume in cc) in either reconstructed-chest-wall target or the skin structure, to reconstruction complications; whether for protons or photons patients.

Conclusion: For patients receiving single-stage DTI reconstruction with and without PMRT, pre-pectoral implant placement had similar rates of complications and reconstruction failure compared to subpectoral reconstruction. Protons compared to Photons did not increase the risk of infection/necrosis but significantly increased capsular-contracture risks.