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Background: Multi-beam IMRT enhances the therapeutic index by increasing the dosimetric coverage of the targeted tumor tissues while minimizing volumes of adjacent organs receiving high doses of RT. The tradeoff is that a greater volume of lung is exposed to low doses of RT, raising concern about the risk of radiation pneumonitis (RP).Methods: Between 7/2010-1/2013, patients with node-positive breast cancer received inverseplanned, multibeam IMRT to the breast/chest wall and regional nodes including the internal mammary nodes (IMN). The primary endpoint was feasibility, predefined by dosimetric treatment planning criteria. Secondary endpoints included the incidence of ≥ grade 3 RP and changes in pulmonary function measured by CTCAE v3.0 scales, pulmonary function tests (PFTs) and

Background The relative contribution of biologic subtype to locoregional recurrence (LRR) in patients who have been treated with neoadjuvant chemotherapy (NAC), mastectomy and postmastectomy radiotherapy (PMRT) is not clearly defined. Methods 233 patients with Stage II-III breast cancer received NAC, mastectomy and PMRT between 2000-2009: 53% (n=123) had HR+ (ER or PR+/HER2−), 23% (n=53) had HER2+ (HER2+/HR+ or HR−), and 24% (n=57) had triple negative disease (TN: HR−/HER2−). The 5-year LRR rates were estimated by Kaplan-Meier methods. Cox regression analysis was performed to evaluate covariates associated with LRR. Results Median follow-up was 62 months. A pathologic complete response (pCR) was seen in 14% of patients. The 5-year LRR rate was 8% in the entire cohort. The LRR rate was 0% in patients with a pCR versus 9% in patients without a pCR (p=0.05). TN disease (HR=4.4, p=0.003) and pathologic node positivity (HR=9.8, p=0.03) were associated with LRR. Patients with TN disease had a higher LRR rate compared to patients with HER2+ and HR+ disease (20% versus 6% and 4%, p=0.005). In patients without a pCR, TN subtype was associated with increased LRR (26% versus 7% HER+ and 4% HR+, p<0.001). Conclusions Patients with TN breast cancer had the highest LRR rate after NAC, mastectomy and PMRT. While no LRR was observed in TN patients with pCR, TN patients with residual disease had significantly higher LRR risk. Patients with HR+ and HER2+ breast cancer had favorable LRR rates, regardless of NAC response, likely due to receipt of adjuvant systemic targeted therapies.

High rates of locoregional control (5-year rate, 98 %) were observed among patients who received trastuzumab and mastectomy ± PMRT. Trastuzumab decreased LRR in HER2-positive women who received mastectomy and PMRT, suggesting that the largest benefit is seen in a higher-risk subset of patients.

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