Delimitation and dosimetry of cardiac substructures in radiation therapy for breast cancer. State of the art.

Abstract

Radiotherapy (RT) is an essential component in the treatment of early breast cancer, with proven benefits in local control and overall survival (OS). However, incidental exposure of the heart and its substructures (SS) to radiation can lead to radiation-induced heart disease (RIHD), a late complication with increasing clinical impact. This narrative review aims to analyze the current evidence on the anatomical delimitation of SC and its correlation of dosimetry with cardiovascular events in patients treated with external RT using modern techniques (3D-CRT, IMRT, VMAT). Recent studies and international guidelines were reviewed, prioritizing clinical and dosimetric evidence in breast cancer; however, primary studies on lung, esophagus, and lymphoma were also reviewed. Critical SCs were identified, such as the left anterior descending artery (LADA), the left ventricle (LV), the atria, and the pericardium, whose exposure is associated with coronary events, heart failure, arrhythmias, and pericarditis. Parameters such as V15Gy≥10% in the LCA and V25Gy≥4% in the LV have been shown to have greater predictive value than the mean cardiac dose (MCD), traditionally used as the sole dosimetric marker. The integration of serum biomarkers (troponins, BNP, galectin-3) and advanced imaging techniques such as ultrasound with an emphasis on cardiac strain allows for the early detection of subclinical dysfunction and the implementation of individualized cardioprotective strategies. It is concluded that SC dosimetry represents a key advance in the personalization of thoracic RT, with clinical, educational, and research implications. Its routine implementation could reduce cardiac toxicity and improve cardiovascular outcomes in cancer patients.