Patients with left-sided breast cancer treated with breast conserving surgery are prospectively enrolled. Two types of radiation treatment are delivered based on attending physician's preferences: radiation to whole breast +- regional nodal areas with free-breathing technique, or with deep inspiration breath-hold (DIBH) technique. The cardiac dose parameters including heart dose and the dose to left anterior coronary artery are assessed, and the cardiac toxicities regularly assessed with cardiac enzymes,electrocardiogram(ECG) and normal gated single-photon emission computed tomography-myocardial perfusion imaging before, during and after radiation.The dose-effect relationship of heart injuries is analyzed.
