ESTRO 2021 Abstract Book

S947

ESTRO 2021

A. Fodor 1 , C. Brombin 2 , P. Mangili 3 , M. Pasetti 1 , R. Tummineri 1 , B. Longobardi 3 , F. Zerbetto 1 , R. Castriconi 3 , P.G. Esposito 3 , S. Broggi 3 , I. Dell'Oca 1 , C.L. Deantoni 1 , A. Sanchez Galvan 1 , L. Perna 3 , A.M. Deli 1 , A. Chiara 1 , P.M.V. Rancoita 2 , C. Fiorino 3,4 , A. Del Vecchio 3 , M.S. Di Serio 2 , N.G. Di Muzio 1,4 1 IRCCS San Raffaele Scientific Institute, Department of Radiation Oncology, Milan, Italy; 2 Vita-Salute San Raffaele University, University Center for Statistics in the Biomedical Sciences, Milan, Italy; 3 IRCCS San Raffaele Scientific Institute, Medical Physics, Milan, Italy; 4 Vita-Salute San Raffaele University, Radiotherapy, Milan, Italy Purpose or Objective This analysis aimed to identify factors associated with acute and late skin toxicity in a large cohort of early- stage breast cancer (BCA) patients (pts) treated with breast conservative surgery and whole breast hypofractionated (WBH) adjuvant forward-planned intensity modulated radiotherapy (F-IMRT) without boost. Materials and Methods From February 2009 to May 2017 1325 consecutive BCA pts (pTis-pT2, pNx-N1a, cM0) were treated with WBHF- IMRT, to a total dose of 40.05 Gy/15 fractions delivered in 3 weeks, without boost. A median number of 4 segments was used (2-11) within a tangential two field three-dimensional conformal irradiation technique to obtain a homogeneous target dose distribution as well as reduced doses to organs at risk. Median age was 62 (interquartile range-IQR-:51.2-70.5) years. Right sided were 48.3% and left sided 51.7% (1.8% had bilateral tumor). Histology was in situ for 8% of pts and invasive in 92%. Chemotherapy was prescribed in 28% of pts, hormonal therapy in 80.3% and monoclonal antibodies in 8.3%. Acute toxicity was evaluated with RTOG scale, late toxicity with SOMA-LENT scale. Results Acute toxicity (erythema) was: 69.7% grading (G)1, 14.2% G2 and 1.5% G3. In 4% of pts maximal acute toxicity was postponed 7-10 days after the end of the treatment. Median follow up was 72.43 (IQR: 44.63-104.13) months. Late toxicity was divided into edema and hyperpigmentation, which improved over time and were observed in 33.1% of patients (28.5% G1, 4.3% G2, 0.2% G3, 0.1% G4), and atrophy, fibrosis, teleangiectasia, and pain, that persist over time, observed in 18.5% of patients (14.4% G1, 3.2% G2, 0.8% G3 and 0.1% G4). Aesthetic result after surgery was evaluated using the Harvard 4-point breast cosmesis scale and was excellent in 28.7%, good in 41.5%, acceptable in 20.3% and poor in 9.5% of pts. Change in breast appearance after radiotherapy was separately evaluated (clinically and with photographs) and was mild in 6.9%, moderate in 2.3% and marked in 1.3% of pts (see image 1 with G3 teleangiectasia and image 2 with G4 atrophy and fibrosis). Median target volume was 642.30 (445.50-916.61) cc and had a significant impact on acute toxicity [OR=2.05, 95% CI for OR: (1.61, 2.60), p<0.001], late edema and hyperpigmentation [OR=1.489, 95% CI for OR: (1.19, 1.87), p<0.001] and teleangiectasia/fibrosis [OR= 1.55, 95% CI for OR: (1.17, 2.05), p <0.001]. Patients treated with sequential or concomitant chemotherapy had an odd ratio 3.5 times higher of having acute G2/G3 toxicity.