ESTRO 2023 - Abstract Book

S166

Saturday 13 May

ESTRO 2023

We conducted a prospective register of postoperative OWHRT for breast cancer patients. All patients were treated with either conformal or IMRT/VMAT and image guide radiotherapy (IGRT) with a dose of 26Gy/5.2Gy to whole breast/thoracic wall, and if indicated, lymph node areas, and a SIB of 29Gy/5,8Gy for tumor bed. Tolerance was evaluated at 1 month and 3 months after finishing OWHRT and every 6 months thereafter and graded according to RTOG/EORT and LENT/SOMA criteria. Results From may 2020 to April 2021, 242 female patients with a median age of 60±12 were included. Complete characteristics of enrolled patients are detailed in Table 1. A total of 183p (76%) were treated with SIB and 123p (51%) underwent RNI and IMC. With a median follow-up of 20 months (16-23 months), acute skin toxicity at one month was: grade 1 in 113p (47%) and grade 2 in 64p (27%) with no cases of ≥ grade 3 toxicity. In the group of patients undergoing RNI , 36p (15%) reported grade 1 and 2p (0,8%) grade 2 esophagitis. No relationship was found between RNI with higher acute-skin-toxicity (Chi square p=0.001). None of the patients presented acute pulmonary or cardiac toxicity. At more than three months 225 patients continue follow-up (late effects). Skin-toxicity occurred in 37p (16,44%) grade 1 and 2p (0,9%) grade 2, pain 3p (1,3%) grade 1 and 4p (1,8%) grade 2 (Table 2), and none presented esophageal, pulmonary or cardiac toxicity.

Conclusion This initial results shows that OWHRT with SIB for WB/CWI and RNI with IMC seems to be feasible and well tolerated. Future studies with larger number of patients and longer follow-up are needed to confirm this results. PD-0231 Acute toxicity after the 5-fraction versus 15-fraction radiotherapy regimen for early breast cancer D. Mink van der Molen 1 , M.C. Batenburg 1 , T. van 't Westeinde 2 , I.E. van Dam 2 , I.O. Baas 3 , L.M. Veenendaal 4 , W. Maarse 5 , M. Sier 6 , E.J. Schoenmaeckers 7 , J.P. Burgmans 8 , R.M. Bijlsma 9 , S. Siesling 10 , A. Doeksen 11 , H.M. Verkooijen 1 , L.J. Boersma 12 , F. van der Leij 2 1 University Medical Centre Utrecht, Division of Imaging and Oncology, Utrecht, The Netherlands; 2 University Medical Centre Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands; 3 University Medical Centre Utrecht, Department of Medical Oncology, Utrecht, The Netherlands; 4 Alexander Monro Hospital, Department of Surgery, Bilthoven, The Netherlands; 5 University Medical Centre Utrecht, Department of Plastic, Reconstructive and Hand Surgery, Utrecht, The Netherlands; 6 St. Antonius Hospital, Department of Surgery, Nieuwegein, The Netherlands; 7 Meander Medisch Centrum, Department of Surgery, Amersfoort, The Netherlands; 8 Diakonessenhuis Utrecht, Department of Surgery, Utrecht, The Netherlands; 9 University Medical Centre Utrecht, Cancer Centre, Department of Medical Oncology, Utrecht, The Netherlands; 10 Netherlands Comprehensive Cancer Organisation (IKNL), Department of Research and Development, Utrecht, The Netherlands; 11 St. Antonius Hospital, Department of Surgery, Utrecht, The Netherlands; 12 Maastricht University Medical Centre+, Department of Radiation Oncology (Maastro), GROW-School for Oncology and Reproduction, Maastricht, The Netherlands

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