Hypofractionated radiotherapy after breast-conserving surgery. Clinical and dosimetric factors predictive of acute skin toxicity

The purpose of this study was to evaluate acute skin toxicity in early breast cancer patients treated with hypofractionated radiotherapy (HFRT) after breast-conserving surgery and to identify factors predictive for grade ≥ 2 acute skin toxicity. A monocentric retrospective study was carried out using cases treated between December 2017 and November 2020. We analyzed data from 202 patients with early breast cancer treated with 3D hypofractionated RT (40.05 Gy in 15 fractions) to the whole breast with or without regional lymph nodes, followed by 13.35 Gy in 5 fractions to the tumor bed. Acute skin toxicity was monitored during RT according to CTCAE (common toxicity criteria for adverse events) scale. Univariate and multivariate analyses were performed to assess predictive factors of acute skin toxicity. Overall, there was no erythema in 9%, grade 1 erythema in 64.5%, grade 2 in 24%, and grade 3 in 2.5%. No grade 4 erythema was seen. Median delay between RT initiating and maximum skin reaction was 22 days (range 4-44 days). No patient interrupted treatment. In univariate analysis, the rate of acute skin toxicity grade 2--3 (G2-3) was significantly higher for patients with larger tumor size (p = 0.02), body mass index > 27 (p = 0.04), and time between chemotherapy (CT) and RT less than 20 days (p = 0.01). Dosimetric risk factors for acute skin toxicity G2-3 were breast volume > 800 cc (p = 0.000), boost volume > 18 cc (p = 0.002), V105% > 40 cc (p = 0.03), and Dmax > 56 Gy (p = 0.007). CT, trastuzumab, regional lymph node radiation, and age were not correlated with increased skin toxicity. In multivariate analysis, acute skin toxicity correlated with T stage (p = 0.032), breast volume > 800 cc (p = 0.012), boost volume > 18 cc (p = 0.04), and Dmax > 56 Gy (p = 0.035). Our results confirm that whole breast with or without lymph nodes hypofractionated RT is safe and well tolerated. The factors strongly associated with a decreased risk of G2-3 skin toxicity are T1, breast volume < 800 c, boost volume < 18 cc, and Dmax < 56 Gy. Long-term follow-up is needed to evaluate late toxicity.