Prospective Exploratory Analysis of Cardiac Biomarkers and Electrocardiogram Abnormalities in Patients Receiving Thoracic Radiation Therapy with High-Dose Heart Exposure

Introduction: Acute effects of incidental cardiac irradiation in patients treated for thoracic cancer are not well characterized. We evaluated longitudinal changes in cardiac biomarkers for patients undergoing conformal radiation therapy (RT) with thoracic malignancies with high-dose cardiac exposure. Methods: Twenty-five patients enrolled in a prospective trial (February 2009-December 2012) received more than or equal to 45 Gy to the thorax, with pretreatment estimates of more than or equal to 20 Gy to the heart. Chemotherapy was allowed except for doxorubicin or fluorouracil. Electrocardiographic (ECG), troponin-I (TnI), and brain natriuretic peptide (BNP) measurements were obtained before RT, within 24 hours of the first fraction, at the end of RT, and at first follow-up (1-2 months). These biomarkers were quantified at specific times and changes from baseline were evaluated with paired t tests. Results: The median heart dose was 25.9 Gy (range 10.1-35.1 Gy). After the first RT fraction, no changes were noted in ECG or median TnI or BNP levels; at the end of RT, two patients had elevated TnI and BNP, but neither difference was statistically significant. At first follow-up, TnI had returned to normal but the median BNP remained elevated (p = 0.042). BNP did not increase over time in the 18 patients who received only RT. Twelve patients experienced acute ECG changes during RT, which resolved in seven patients by the next measurement. No patients experienced clinically significant RT-related events. Conclusion: Increases in BNP and ECG changes were observed during high doses of radiation to the heart. The findings of this pilot study warrant further investigation and validation.