ESTRO 2023 - Abstract Book

S1040

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ESTRO 2023

histological G3 (3.6%). If solely a SNB was performed, 48.3% of negative respondents would consider RNI. If a SNB was performed, 39.1% considered that >3 AN would be sufficient to omit ALND, while 40.9% considered 1-3 AN. 71.4% of respondents would consider a hypofractionated scheme for RNI. Conclusion Practice regarding RNI differs greatly between RT Departments, even within the same country. Most RO would consider RNI in a patient with clinically involved AN with complete pathological response after NST, especially when in presence of high risk factors, even if ALND was performed. Hypofractionated schemes for RNI are well established and can be a safe option. Trials are needed to identify which subgroups are most likely to benefit from RNI in the post NST setting. C. Garcia Zanoguera 1,2 , J. Gadea Quinteiro 1,2 , A.G. Curbelo Artiles 1 , L. Mateu Castell 1 , I. Ortiz Gonzalez 1 , J. Pardo Masferrer 1,2 1 Hospital Universitario Son Espases, Servicio de Oncología Radioterápica, Islas Baleares, Spain; 2 IdiSBa, Institut d’Investigació Sanitaria de les Illes Balears, Islas Baleares, Spain Purpose or Objective The phase 3 FAST-Forward trial reported that 26Gy in 5 fractions (fx) over 1 week for early-breast cancer patients after breast conserving surgery was non-inferior to the standard 40Gy in 15fx over 3 weeks for local tumor control and normal tissue effects. In this study, a sequential tumor bed boost was allowed (10 or 16Gy in 2Gy/fx) if required. The aim of our study is to evaluate the safety and feasibility of a simultaneous integrated boost (SIB) up to 29/30Gy over 5fx in order to avoid treatment lengthening when a boost is indicated. Materials and Methods From March 2020 to December 2021, 126 patients eligible for 5fx-RT schedule were referred to our institution and selected for the analysis. A SIB to the tumor bed up to 29Gy in 5fx of 5.8Gy was indicated when any of the following criteria appeared: Age < 60 years, high-grade tumors and lymphovascular or perineural invasion. When positive margins were observed in the histological exam, a SIB up to 30Gy in 5fx of 6Gy was prescribed. Patient´s toxicity was assessed at 4 different points: During RT and at 1, 6 and 12 months follow-up. Toxicity was evaluated using CTCAE 5.0 criteria. Results Mean follow-up was 6.25 months and mean age was 56 years (32-83). During RT course, no toxicities were observed. G1-2 dermatitis was observed in 9 patients at first month assessment, but all of them had disappeared at 6 months after RT. According to skin-color changes, 11% of the patients presented skin hyperpigmentation at first month assessment but in most cases was not observed in subsequent evaluations. Only 4% of the patients presented G1 fatigue and skin induration in the first medical visit after RT. No severe toxicities were found in any patient at any time during follow-up. Complete details are shown in table 1. In addition, one patient developed mastitis during the first month after RT but was easily solved with oral antibiotics. PO-1297 Safety & feasibility of SIB in extreme 1-week hypofractionated radiotherapy for early breast cancer

Conclusion According to our data, administration of SIB up to 29/30Gy in 5fx is safe and feasible for early-breast cancer patients requiring adjuvant RT after breast conserving surgery. SIB could replace sequential boost in these patients shortening the RT treatment and improving patients’ compliance and comfort. Further follow-up is needed in order to assess chronic toxicity.

PO-1298 Clinical predictors of dosimetric precedence for (DIBH) radiation therapy for breast cancer

S. Abdelqader 1 , F. Abuhijli 2 , R. Abuhijlih 2 , H. Al-Masri 2 , H. Kana'an 3 , A. Alnsour 4 , S. Mheid 2 , I. Mohamad 2 , H. Abdel-Razeq 5

1 king Hussein Cancer Center, Radiation Oncology, Amman , Jordan; 2 king Hussein Cancer Center, Radiation Oncology , Amman, Jordan; 3 king Hussein Cancer Center, Radiation Oncology, Amman, Jordan; 4 king Hussein Cancer Center, Radiation Oncology , Amman , Jordan; 5 king Hussein Cancer Center, Medical Oncology , Amman, Jordan Purpose or Objective We aim to evaluate the variables influence the effect of deep inspiration breath hold (DIBH) during left breast cancer radiation therapy (RT). Materials and Methods Consecutive patients who underwent CT simulation for adjuvant left breast RT between 2019 and 2021, using a free breathing (FB) and DIBH techniques, were reviewed. For each patient, target and organs at risk volumes were contoured