ESTRO 2025 - Abstract Book

S462

Clinical - Breast

ESTRO 2025

Purpose/Objective: Adjuvant breast radiotherapy reduces breast cancer-specific mortality but has historically been associated with increased cardiac toxicity due to significant cardiac exposure from older two-dimensional (2D) and three dimensional (3D) radiotherapy techniques. Studies by Darby et al. established a linear relationship between the mean heart dose (MHD) and the risk of ischemic cardiac events. However, with modern techniques like intensity modulated radiotherapy (IMRT), including helical tomotherapy, the dose distribution to cardiac structures differs, potentially altering the relationship between MHD and cardiac toxicity. This study assesses long-term cardiac toxicity in a cohort treated with helical tomotherapy to determine the relevance of 3D-derived dose constraints in IMRT. Material/Methods: All breast cancer patients treated with helical tomotherapy at the Institut Curie from August 2010 to December 2015 were included. Patients were treated after breast-conserving surgery or mastectomy, with some receiving neoadjuvant or adjuvant chemotherapy, including trastuzumab for HER2-positive tumors. Tomotherapy was indicated for patients with challenging anatomical conditions or target volumes. The primary endpoint was cardiac toxicity correlated with MHD. Secondary endpoints included overall and disease-specific survival. Statistical analysis involved logistic regression and Cox proportional hazards models. Results: Among 179 patients, the median MHD was 7.04 Gy, with 95.6% of patients having an MHD above 5 Gy. Sixty-six patients had at least one cardiovascular risk factor, and 28.5% had a BMI over 30. With a median follow-up of 9.1 years, eight patients (4.5%) experienced cardiovascular events (Table 1): two major coronary events (MACE), five cases of heart failure, and one arrhythmia. All these patients had pre-existing risk factors or obesity, and no significant correlation was found between MHD and MACE (p=0.607) or heart failure (p=0.800). Cardiac mortality was absent, with a 10-year overall survival of 88.0% and disease-specific survival of 94.3%.