ESTRO 2025 - Abstract Book

S533

Clinical - Breast

ESTRO 2025

Material/Methods: Between 2/2020 and 8/2023 55 patients (27 to 70 years old, mean 47.1, SD 10.9) with left-(n= 30) and right-(n= 25) sided breast cancer underwent echocardiography and laboratory examination immediately before (t0) and 3, 6 and 12 months (t3; t6; t12) following completion of radiation. 31 patients (57%) received chemotherapy; 9 patients (16%) were treated with herceptine. Modern radiotherapy techniques (intensity modified radiation therapy – IMRT; gating for patients with left sided therapy) were applied in all patients. We investigated echocardiographic parameters for left ventricular function (ejection fraction - LVEF and strain rate - SR) and right ventricular function (TAPSE). In addition, cardiac-specific laboratory parameters (TroponinT – TropT and NT-pro-brain natriuretic peptide – NTproBNP) and high sensitivity CrP-values were assessed. Results: We did not observe any significant changes in laboratory parameters over the treatment time. TAPSE as a measure of global right ventricular function also showed no statistically significant changes over time (linear mixed model: β time = 0.33 [-0.09, 0.74], p = 0.122). LVEF tended to decrease over time, reaching its minimum at 12 months (t0: 62.2% SD 3.76; t3: 61.5% SD 4.21; t6: 62.3% SD 4.59; t12 59.7% SD 4.1; β time = -0.63 [-1.12, -0.14], p = 0.0131). We also observed statistically significant worsening of left ventricular strain rate for patients with right sided (β time = 0.30 [- 0.03, 0.57], p = 0.0335) and – even more pronounced – also patients with left sided radiotherapy (β time = 0.58 [0.28, 0.88], p = 0.000275). Conclusion: Despite the use of modern radiotherapy techniques, thoracic radiotherapy leads to significant alterations of left ventricular function. Worsening of strain rate as an early and very sensitive indicator of subclinical myocardial damage in patients with breast cancer indicates vulnerability of the myocardium to radiotherapy and emphasizes the need for continuous monitoring of cardiac function during long term follow-up. Further analysis has to reveal the impact of cardiotoxic systemic therapies as well as preexisting cardiac co-morbidities and dosimetric parameters of radiation therapy for long term cardiac function. Digital Poster Atrial fibrillation after radiotherapy for breast cancer: the Watch Your HeaRT Study (WATCH) Laura Saint-Lary 1 , Gaëlle Jimenez 2 , Baptiste Pinel 2 , Jérémy Camilleri 2 , David Broggio 3 , Marie-Odile Bernier 1 , Corinne Mandin 1 , Loïc Panh 4 , Serge Boveda 4 , Youila Kirova 5 , Juliette Thariat 6 , Sophie Jacob 1 1 PSE-SANTE/SESANE/LEPID, Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Fontenay-aux-Roses, France. 2 Department of Radiation Oncology, Clinique Pasteur, Toulouse, France. 3 PSE-SANTE/SDOS, Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Fontenay-aux-Roses, France. 4 Cardiology and Heart Rhythm Management Department, Clinique Pasteur, Toulouse, France. 5 Department of Radiation Oncology, Institut Curie, Paris, France. 6 Department of Radiation Oncology, Centre François Baclesse, University of Caen Normandie, Caen, France Purpose/Objective: Post-radiotherapy atrial fibrillation (AF) in breast cancer patients is a relatively new and understudied topic. These arrhythmias, associated with high-impact health pathologies (stroke, heart failure, dementia), compromise patients' quality of life and survival. Detection of AF is therefore essential for optimal management and smartwatches with ECG capability could represent a promising tool in cardio-oncology. Based on this technology, the objective of the WATCH study is to evaluate the risk of post-radiotherapy AF for breast cancer patients and to identify risk factors and cardiac radiation exposure associated with these complications. Keywords: adjuvant radiotherapy, cardiotoxicity, LV function 2514