The effect of breast volume on toxicity using hypofractionated regimens for early stage breast cancer for patients

PURPOSE: Hypofractionated radiation therapy (HFRT) remains underused, despite multiple randomized trials showing the equivalence of HFRT to conventional fractionated radiation therapy (CFRT). We sought to retrospectively review the relationship between breast volume and toxicity for HFRT versus CFRT. METHODS AND MATERIALS: Data from 114 patients who received a diagnosis of early stage breast cancer and were treated with lumpectomy and whole breast radiation alone were reviewed. Breast cancer laterality, stage, grade, estrogen/progesterone receptor and human epidermal growth factor receptor 2 status, and systemic therapy use were recorded. Length of follow-up was calculated using the last day of radiation treatment and the date of the most recent follow-up. RESULTS: The median follow-up was 42 months. A total of 83 patients were treated with HFRT and 31 with CFRT. Rates of grade ≥2 skin toxicity were significantly higher in patients undergoing CFRT compared with HFRT (76% vs 28%; P < .0001). In a subset of patients with breast volume ≥1000 cm(3), grade ≥2 skin toxicity trended higher for CFRT patients (73% vs 38%; P = .057). For posterior separation >25 cm, the percentage of patients with grade 2 skin toxicity was 43% for HFRT versus 57% for CFRT (P = .67). The volume of breast tissue receiving >105% of the total prescription dose, including boost, was not significantly different for HFRT versus CFRT (P = .70). CONCLUSIONS: Use of HFRT resulted in lower acute skin toxicity rates compared with CFRT. Large breast size (volume ≥1000 cm(3)) was associated with lower acute grade 2 toxicity with the use of HFRT despite achieving similar dosimetry compared with CFRT.