Objectives: The study aimed to evaluate the dose delivered to the heart during radiotherapy of left-sided and right-sided breast cancer (BC) patients, correlate the dose and laterality of radiotherapy to the possible cardiac damage and evaluate whether Left-ventricular Ejection Fraction (LVEF), Troponin-I (TnI), Creatinine Kinase (CK), Creatine Kinase-MB Relative Index (CK-MBRI) or Lactic Dehydrogenase (LDH) could be used to detect the possible onset of radiotherapy-related cardiotoxicity.Subjects and methods: 80 females were assigned as; 30 left-sided BC patients, 30 right-sided BC patients and 20 healthy females. Patients were treated by radical mastectomy followed by FAC-based chemotherapy and radiotherapy. CT-based 3D-planning was used to generate cardiac dose-volume histograms to assess mean dose received by the heart.Echocardiography was done to all patients before and 1 year after completing radiotherapy. In serum, TnI and CK-MB concentration and CK and LDH activities were determined before and 1 year after radiotherapy.Results: In left-sided patients, mean dose delivered to the heart was significantly higher in left-sided patients with significant association with total radiotherapy dose in left- but not right-sided patients. LVEF before and after radiotherapy were statistically different only in left-sided patients. LVEF one year after radiotherapy dropped 20% or more (△LVEF) in 6 patients, all were left-sided. Using cut-off values 0.08 ng/mL for TnI and 1.4 for CK-MBRI; 11 left-sided patients had abnormal TnI and CK-MBRI vs 5 right-sided patients, the 6 patients identified with △LVEF ≥ 20 were all among them.Conclusion: the mean dose delivered to the heart is significantly higher in left-sided patients, and it was correlated to the total radiotherapy dose. One year after radiotherapy, △LVEF is possibly good marker of cardiotoxicity onset, however, the persistent elevation of both TnI and CK-MBRI could identify both patients with cardiotoxicity and patients that are thought to be in subclinical phase of cardiac damage.Keywords: Breast cancer, Radiation-induced cardiac damage, LVEF, Troponin ICK-MB relative index, LD
