P8. Comparative Outcomes of Proton versus Photon Post-Mastectomy Radiation Therapy in Pre-pectoral Implant Based Breast Reconstruction

PURPOSE: The rising popularity of Pre-Pectoral Implant-Based Breast Reconstruction (PP-IBBR) and proton radiation lacks outcomes data. We aim to compare complications in PP-IBBR with proton versus photon Post-Mastectomy Radiation Therapy (PMRT). METHODS: A single-institution retrospective study included patients undergoing PP-IBBR followed by PMRT (January 2020-October 2022). Complications were minor infection (requiring oral antibiotics), major infections (requiring intravenous antibiotics), wound complications, implant exposure, flap necrosis, seromas, re-operations, capsular contracture, and implant failures. RESULTS: 114 patients; one patient had bilateral implants. 115 PP-IBBR receiving PMRT were analyzed in two cohorts: photon (n=74) and proton (n=41) PMRT. Photon PMRT showed more complications compared to proton PMRT. Baseline clinical characteristics were not significantly associated with more complications in univariate analysis. Multivariable model adjusting for stage showed photon PMRT was a significant predictor of ≥ 2 more complications. Stage 3 patients were significantly associated with ≥ 2 or more complications. CONCLUSION: Compared to photon PMRT, proton PMRT had fewer complications in patients with PP-IBBR. Proton PMRT is a safer option, warranting further studies with larger cohorts.