Hypofractionated whole-breast radiotherapy in large breast size patients: is it really a resolved issue?

The purpose of this study was to evaluate the impact of breast size on acute and late side effects in breast cancer (BC) patients treated with hypofractionated radiotherapy (Hypo-RT). In this study we analyzed patients over 50 years with a diagnosis of early BC, candidate for Hypo-RT after conservative surgery. Acute and late skin toxicities were evaluated in accordance with the RTOG scale. Multivariable logistic analysis was performed using dosimetric/anatomical factors resulted associated with toxicity outcome in univariable analysis. Among patients treated between 2009 and 2015, 425 had at least 5 years of follow-up. At RT end, acute skin toxicity ≥ G2 and edema ≥ G2 occurred in 88 (20.7%) and 4 (0.9%) patients, respectively. The multivariable analysis showed association of skin toxicity with boost administration (p < 0.01), treated skin area (TSA) receiving more than 20 Gy (p = 0.027) and breast volume receiving 105% of the prescription dose (V105%) (p = 0.016), but not breast size. At 5 years after RT, fibrosis ≥ G1 occurred in 89 (20.9%) patients and edema ≥ G1 in 36 (8.5%) patients. Fibrosis resulted associated with breast volume ≥ 1000 cm³ (p = 0.04) and hypertension (p = 0.04). As for edema, multivariable logistic analysis showed a correlation with hypertension and logarithm of age, but not with boost administration. Breast volume had an unclear impact (p = 0.055). A recurrent association was found between acute and late toxicities and breast V105%, which is correlated with breast size. This may suggest that a more homogenous RT technique may be preferred for patients with larger breast size.