ESTRO 2023 - Abstract Book

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ESTRO 2023

In our experience the use of bolus in patients with locally advanced breast cancer receiving moderately hypofractionated radiation therapy was overall safe, well tolerated, and associated with mild toxicity.

PO-1262 Non-inferior local control of IMRT-SIB compared to 3D-CRT-seqB - 5-year results of a phase III trial

T. Forster 1 , M.F. Häfner 1 , N. Arians 1 , L. König 1 , S.B. Harrabi 1 , I. Schlampp 1 , F. Weykamp 1 , E. Meixner 1 , K. Lang 1 , V. Heinrich 2 , N. Weidner 2 , J. Hüsing 3 , M. Wallwiener 4 , M. Golatta 4 , A. Hennigs 4 , J. Heil 4 , H. Hof 5 , D. Krug 6 , J. Debus 1 , J. Hörner-Rieber 1 1 Heidelberg University, Radiooncology, Heidelberg, Germany; 2 Tübingen University, Radiooncology, Tübingen, Germany; 3 Heidelberg University, Division of Biostatistics, Heidelberg, Germany; 4 Heidelberg University, Gynecology, Heidelberg, Germany; 5 Strahlentherapie Rhein-Pfalz, Radiooncology, Neustadt, Germany; 6 Kiel University, Radiooncology, Kiel, Germany Purpose or Objective The IMRT-MC2 trial was conducted to demonstrate non-inferiority of conventional fractionated intensity-modulated radiotherapy with simultaneous integrated boost (IMRT-SIB) to 3-D-conformal radiotherapy with sequential boost (3-D-CRT seqB) for adjuvant breast radiotherapy. Materials and Methods A total of 502 patients were randomized between 2011 and 2015 for the prospective, multicenter, randomized phase-III trial (NCT 01322854). 5-year results of late toxicity (LENT-SOMA), overall survival, disease-free survival, distant cancer free survival, cosmesis (Harvard scale) and local control (non-inferiority margin at hazard ratio of 3.5) were analyzed after a median follow-up of 62 months. Results The 5-year LC rate for the IMRT-SIB arm was non-inferior to the control arm (98.7% vs. 98.3%, respectively; HR 0.582, 95%- CI: [0.119-2.375], p=0.4595). Furthermore, there was no significant difference in overall survival (97.1% versus 98.3%, respectively; HR 1.235, 95%-CI: [0.472-3.413], p=0.6697), disease-free survival (95.8% versus 96.1%, respectively; HR 1.130, 95%-CI: [0.487-2.679], p=0.7758) and distant cancer-free survival (97.0% versus 97.8%, respectively; HR 1.667, 95%-CI: [0.575-5.434], p=0.3601). After 5 years, the late toxicity and cosmetic assessment showed no significant differences between treatment arms. Conclusion The 5-year results of the IMRT-MC2 trial provide strong evidence, that the application of conventionally fractionated IMRT SIB for breast cancer patients is both safe and effective with non-inferior local control compared to 3-D-CRT-seqB. 1 Institute of Oncology Ljubljana, Division of Radiation Oncology, Medical faculty, University of Ljubljana, Ljubljana, Slovenia; 2 Radiation Oncology Unit - Oncology Department, Azienda Ospedaliero Universitaria Careggi, Department of Experimental and Clinical Biomedical Sciences "M. Serio", University of Florence, Florence, Italy; 3 Institute of Oncology Ljubljana, Division of Radiation Oncology, Ljubljana, Slovenia Purpose or Objective There is limited data on the role of the metastases-directed radiation therapy (MDRT) in repeat or induced oligometastatic breast cancer (OMBC). The purpose of this work is to investigate the effectiveness of MDRT (stereotactic body radiation therapy, SBRT vs. conventionally fractionated palliative radiotherapy, CFRT) in patients with OMBC. Materials and Methods For patients with OMBC, we performed a two-institutional retrospective data collection. ESTRO EORTC classification was used to characterize oligometastatic disease (OMD) states. Primary endpoint was time to next (systemic) treatment (TTNT) as a surrogate for the duration of clinical benefit. Other outcomes included local control rate (LCR), overall survival (OS) and progression-free survival (PFS), calculated from the beginning of MDRT. Results We have included 56 patients with 78 treated lesions. The median age was 60 years old (range, 39–88). Surrogate breast cancer subtypes were as follows: 37 (66.1%) hormonal positive (HR+) human epidermal growth factor receptor 2 negative (HER2-), 11 (19.6%) HR+/HER2+, five (8.9%) HR-/HER2- and three (5.4%) patients had HR-/HER2+ OMBC. Fifteen (26.8%) patients had repeat OMD and 41 (73.2%) induced OMD. OMD lesions were treated with SBRT (n=23; 41.1%) or CFRT (n=33; 58.9%). The median SBRT dose was 35 Gy (20–60) delivered in 3 (1–8) fractions and the median CFRT dose was 30 Gy (8–61), delivered in 10 (1–28) fractions. Compared to patients treated with SBRT, patients treated with CFRT reported higher rates of acute adverse events (AEs) of any grade (21.7% vs. 48.5%; p=0.038) and similar rates of G3 AEs (4.3% vs. 6.1%; p=0.675). Median follow-up post MDRT was 12.1 months (0.2–37.3). For the whole group of patients, TTNT was 7.6 months (1.6–65) and did not differ between the SBRT (6.4 months; 1.6–26.2) or CFRT groups (8.0 months; 3.5–65) (p=0.307), and between repeat (11.0 months; 2.4–26.1) or induced OMD (7.0 months; 1.6–65) (p=0.290). The median time to local progression of the OMD treated lesion was 12.5 months (2.4–51.0). One-year LCR were 100% with SBRT and 81% with CFRT (p=0.109). Overall, 30 (53.6%) patients experienced systemic progression (polymetastatic, n=17; 56.7% and oligometastatic, n=13; 43.3%). 2-year OS was 81% and median PFS was 15.1 months (12.8–17.2). Compared to patients with repeat OMD, patients with induced OMD had statistically worse PFS (Figure 1). PO-1263 The role of radiation therapy in patients with repeat or induced oligometastatic breast cancer I. Ratosa 1 , L. Visani 2 , N. Dobnikar 3 , M. Banini 2 , V. Lorenzetti 2 , G. Frosini 2 , A. Peruzzi 2 , I. Meattini 2