PURPOSE: Our purpose is to explore the effect of postmastectomy radiation therapy (PMRT) modality and timing on complication rates in breast cancer patients receiving immediate 2-stages expander/implant. METHODS AND MATERIALS: We reviewed the charts of 661 patients who underwent immediate 2-stages expander/implant with/without PMRT at our institution from 2000 to 2019. Patients were divided into 3 cohorts: no radiation, PMRT to expanders (RTE), and PMRT to implants after expander exchange (RTI). PMRT was delivered either with 3-dimensional conformal photon with or without chest wall boost (CWB) or proton therapy. Reconstruction complications were defined as infection/necrosis requiring debridement, capsular-contracture requiring capsulotomy, and reconstruction failure requiring prothesis removal. Logistic regression and Cox models were used to assess the effect of different radiation therapy modalities on complication rates and local control. RESULTS: Among 661 patients, 309 (46.7%) received PMRT, 220 of the 309 (71.2%) received RTE before exchange, and 89 (28.8%) received RTI after exchange. Seventeen out of 309 (5.5%) patients received proton therapy. The complications among RTE versus RTI cohorts were 22.7% versus 15.7% for infection/necrosis, 13.6% versus 19.1% for capsular-contracture, and 39.5% versus 31.5% for overall reconstruction failure, respectively. Among proton patients, 8/17 (47%) developed capsular contracture compared with 16.4% (24/146) and 10.3% (15/146) in CWB and non-CWB groups, respectively. Adjusted multivariable analysis showed no significant difference between RTI and RTE in terms of infection/necrosis and capsular contracture. Yet, RTE significantly increased overall reconstruction failure compared with RTI (39.5% vs 31.5%; odds ratio [OR], 2.11; P = .02). Protons significantly increased capsular contracture compared with both CWB and non-CWB groups (OR, 5.4; P = .01 and OR, 10.9; P < .001, respectively). Moreover, proton significantly increased overall reconstruction failure. The 5-year local control rates were 95.3% and 97.7% for RTE and RTI, respectively (hazard ratio, 1.2; P = .7). CONCLUSIONS: Early radiation to the expander before the exchange to implant significantly increased overall reconstruction failure without improving local control. Protons significantly increased capsular contracture rates and overall reconstruction failure leading to more revision surgeries.