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Hypofractionated whole breast radiotherapy is considered the standard after conservative surgery for breast cancer (BCa), but the interest in hypofractionation is growing even for locoregional treatments, involving not only breast/chest wall, but also lymph nodal (LN) areas. We report acute toxicity in patients with advanced BCa treated with hypofractionated radiotherapy (HRT) to breast/chest wall and regional LN in our Institute.

From 03/2018 to 05/2021 132 pts with diagnosis of advanced BCa pts (98% female, 2% male) underwent locoregional HRT after conservative surgery (58%) or mastectomy (40.5%), and 3 pts received radical RT (1.5%). Two pts had bilateral BCa (134 irradiated breasts). Median age was 52 (26-86) years. Molecular subtypes were: Luminal A 29%, Luminal B Her2- 28.5%, Luminal B Her+ 19%, HR negative Her2+ 13% and Triple negative 10.5%. Neoadjuvant chemotherapy was prescribed in 55% of pts, adjuvant in 55%, and concomitant in 11%. Adjuvant hormonal therapy was prescribed in 76% of pts (IA or TMX -/+ LH-RH analogue). Thirty-three % of pts underwent HER2-targeted therapy. Treatments were delivered with 3DCRT (11%), VMAT (30%) or Tomotherapy (59%, TomoDirect or TomoHelical), to a total dose of 40.05 Gy in 15 fractions, delivered in 3 weeks, to breast/chest wall and regional LNs. A simultaneous integrated boost (SIB) up to 48 Gy to the tumor bed was delivered for pts with high-risk local relapse. The target was: whole breast in 60% (46% right, 54% left), chest wall in 40% (40% right, 60% left, 33% without and 67% with post-mastectomy reconstruction), supraclavicular LN in 100%, axillary LN in 34.4%, and internal mammary chain in 13.5% of cases, respectively. A SIB to the tumor bed was delivered in 34.5% of pts. Acute toxicity was registered according to CTCAE v 4.0.

Acute toxicity is summarized in table 1. No patient experienced ≥G3 acute toxicity. No significant differences in toxicity were found between the different RT techniques. G2 skin toxicity was experienced in 13% of pts with SIB and 8% without SIB. Significant increase of G1-G2 skin toxicity and dysphagia were found in pts treated on chest wall with post-mastectomy reconstruction (as summarized in table 2).

Locoregional HRT is feasible with low acute toxicity without significant differences in toxicity between the different RT techniques. Longer follow-up is needed to evaluate late toxicity and local control in the different subgroups of patients.