Impact of Prepectoral Implant Placement and Radiation Modalities (Protons/Photons/Dosimetry) in Mastectomy Patients Undergoing Immediate Single Stage Direct-to-Implant Breast Reconstruction.

[PURPOSE] For patients with breast cancer receiving mastectomy with direct-to-implant (DTI) immediate breast reconstruction, placing the implant in the prepectoral or subpectoral plane remains debatable, especially in settings of postmastectomy radiation therapy (PMRT).

[METHODS AND MATERIALS] We reviewed 3039 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 a photon (3-dimensional-conformal or volumetric arc therapy) or proton therapy, mainly with pencil-beam-scanning. All patients received conventional fractionation (50-50.4 Gy in 25-28 fractions). 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 (ie, no salvage reconstruction); and overall reconstruction failure (removal of the implant for any complication with and without salvage reconstruction). Different subgroup analyses were done.

[RESULTS] A total of 815 patients met inclusion criteria, with an overall median follow-up of 6.2 years. We found that there is no significant difference between prepectoral versus subpectoral for infection/necrosis (odds ratio [OR], 1.5; P = .3); capsular contracture (OR, 0.97; P = .9); absolute reconstruction failure (OR, 1.9; P = .12); and overall reconstruction failure (OR, 1.2; P = .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 = .4) and absolute reconstruction failure (OR, 1.2; P = .7), but there were significantly higher risks for capsular contracture with protons (OR, 4.4; P < .001) and overall reconstruction failure compared with photons (OR, 2.0; P = .05). We did not find a significant correlation pattern between different dosimetry factors (the average dose, the maximum dose, and volume in cubic centimeter) in either the reconstructed chest wall target or the skin structure, about reconstruction complications, whether for proton or photon patients.

[CONCLUSIONS] For patients receiving single-stage DTI reconstruction with and without PMRT, prepectoral implant placement had similar rates of complications and reconstruction failure compared with subpectoral reconstruction. Protons compared with photons did not increase the risk of infection/necrosis but significantly increased capsular contracture risks.