S302
Clinical - Breast
ESTRO 2026
mm in the standard arm, p < 0.0001). The mean delta of the axial distance between PTV and heart was 0.5 cm and 0.4 cm (p < 0.0001), respectively. Patient satisfaction and active engagement were rated as moderate (3/4) in the standard group and as high (4/4) in the R&R group. Conclusion: R&R is a very promising method that achieves significant, measurable improvements in the parameters indicative of improved DIBH performance, including higher total lung volume and larger heart-breast tissue distance, based on better preparation of patients for DIBH in left-sided breast cancer radiotherapy. Keywords: DIBH, respiratory training & relaxation exercises Retrospective multicenter study on adverse events of adjuvant radiotherapy in breast cancer patients treated with Trastuzumab Emtansine (T-DM1) Fiorenza De Rose 1 , Elisabetta Vitali 2 , Barnaba Floreno 3 , Elisa Villa 4 , Roberta Bertolini 5 , Edy Ippolito 6,7 , Sara Lucidi 1 , Daniele Ravanelli 8 , Carlotta Giandini 9 , Maria Carmen De Santis 9 , Andrea Emanuele Guerini 10 , Antonella Ferro 11 , Valentina Vanoni 1 , Stefano Maria Magrini 10 , Michela Buglione di Monale E Bastia 10 1 Radiation Oncology, APSS, Santa Chiara Hospital, Trento, Italy. 2 Radiation Oncology, ASST Ospedale Papa Giovanni XXIII, Bergamo, Italy. 3 Radiation Oncology, Abele Ajello Hospital, Mazara del Vallo, ASP, Trapani, Italy. 4 Radiation Oncology, Humanitas Gavazzeni, Bergamo, Italy. 5 Radiation Oncology, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Rome, Italy. 6 Radiation Oncology, Università Campus Bio-Medico di Roma, Rome, Italy. 7 Radiation Oncology, Fondazione Policlinico Universitario Campus Bio- Medico, Rome, Italy. 8 Medical Physics, APSS, Santa Chiara Hospital, Trento, Italy. 9 Radiation Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy. 10 Radiation Oncology, University and ASST Spedali Civili, Brescia, Italy. 11 Medical Oncology, APSS, Santa Chiara Hospital, Trento, Italy Poster Discussion 3449 Purpose/Objective: This multicenter study aimed to evaluate adverse events of adjuvant radiotherapy (RT) in a real-world series of breast cancer (BC) patients (pts) treated with Trastuzumab Emtansine (T-DM1). Material/Methods: Data were retrospectively collected from pts diagnosed with Her2-positive BC and residual invasive disease after primary systemic therapy (PST), receiving adjuvant T-DM1 during RT, across seven Italian centers. RT was delivered to the breast or chest wall,
Mini-Oral 3373
Can breathing training improve DIBH in radiotherapy for left-sided breast cancer? – Preliminary results of the B-REST trial Rebecca Moser 1 , Lena Marie Buchecker 1 , Nina A. Mayr 2 , Jana Nano 1 , Sophie Maier 1 , Luisa Allwohn 1 , Sophia Kiesl 1 , Sophie Therese Behzadi 1 , Stephanie Elisabeth Combs 1,3 , Kai Joachim Borm 1 1 Department of Radiation Oncology, TUM School of Medicine and Health, Munich, Germany. 2 College of Human Medicine, Michigan State University, East Lansing, USA. 3 Department of Radiation Sciences (DRS), Institute of Innovative Radiotherapy (iRT), Helmholtz Zentrum München, Munich, Germany Purpose/Objective: To address current challenges in optimizing patients’ DIBH performance, the ongoing prospective randomized B-REST trial (NCT05975190) aims to improve patient compliance and quality of deep inspiration breath hold (DIBH), with the goal of further minimize cardiac radiation exposure during left-sided breast irradiation. The trial investigates the efficacy of an active, structured pre-treatment respiratory training program in combination with relaxation exercises (R&R) for patients receiving adjuvant radiotherapy for left-sided breast cancer. Here we present initial results of the first 100 enrolled patients. Material/Methods: All patients underwent planning CT in both free- breathing (FB) and DIBH. Following randomization, and one week prior to the planning CT, patients in the interventional arm received pre-treatment R&R. Patients in the standard arm did not receive any training. Both groups completed structured questionnaires (e.g. EORTC QLQ-C30 and BR-23) at predefined prospective time points. R&R-induced changes in the mean difference (delta) of total lung volume between FB and DIBH (FB–DIBH), mean delta of the minimal sagittal distance between heart and breast tissue (FB–DIBH), and mean delta of the axial distance between the PTV and heart (FB–DIBH) were assessed. Patient satisfaction and active patient integration in the therapy were evaluated on a four- point Likert scale. The study is supported by the German Cancer Aid. Results: Since June 2022, 100 patients have completed their treatment, 51 in the standard and 49 in the interventional arm. The R&R group showed a mean delta in total lung volume of 1834 cm ³ , signifying a mean increase of 239 cm ³ over the standard group (1595 cm ³ , p < 0.0001). Regarding features of cardiac sparing, the mean delta of the minimal sagittal distance between heart and breast tissue was nearly 1 cm larger in the R&R arm ( − 13.2 mm versus − 12.24
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