Hypofractionated whole breast irradiation and simultaneous integrated boost in large-breasted patients: long term toxicity and cosmesis

Abstract Introduction To evaluate the impact of breast size on long-term toxicity and cosmesis in breast cancer patients treated with hypofractionated simultaneous integrated boost (SIB) using volumetric modulated arc therapy (VMAT). Methods Patients with early-stage breast cancer were treated with 3-week hypofractionated SIB-VMAT to the whole breast (40.5 Gy) and tumor bed (48 Gy). Two cohorts were identified: small-medium- ( 1000 cm3). Acute and late (at 2 and 5-year) skin toxicity and cosmetic data were analyzed. Univariate and multivariate analysis evaluated associations between toxicity and dosimetric/anatomical variables. Results From August 2010 to March 2017, a total of 1160 patients were treated, 831 had at least 2-year follow-up and were analyzed. Treated skin area (TSA) receiving at least 20 Gy TSA>400 cm2 and V105%ofBoost>5 cm3 were significant predictors for acute skin toxicity. Multivariate analysis at 2-year was significant for boost volume >70 cm3, TSA>400 cm2 and breast size >1500 cm3. At 5-year (352 patients), none of the analyzed variables was significant. For cosmetic outcome only the breast size (>1000 cm3) and the boost size >70 cm3 at 2- and 5-year, respectively, confirmed significance. Conclusions The TSA>400 cm2 resulted as a significant predictor of both acute and late skin toxicity at 2-year; however, at 5-year no breast size or dosimetric parameter suggested indications for increased toxicity. A worse cosmetic outcome was recorded at 2-year follow up for large breasts, but not confirmed at 5-year. These long-term data suggest that hypofractionated SIB-VMAT is a viable modality also in large-breasted patients.