3093 - Early Biological Response in Cardiac Toxicity: Comparison of Proton and Photon Irradiation
Presenter(s)
K. Liao1, L. Cao2, Y. Lin1, Y. B. Zhang3, and J. Chen1; 1Department of Radiation Oncology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China, 2Shanghai Key Laboratory of Proton Therapy, Shanghai, China, 3Department of Radiation Oncology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, shanghai, China
Purpose/Objective(s): Proton therapy can substantially lower mean cardiac dose than conventional photon therapy in patients receiving thoracic irradiation. However, in most cases, heart radiation exposure cannot be completely avoided with proton therapy. Hence, it is critical to identify the early pathophysiological effect and molecular mechanism following proton beam irradiation to heart so as to optimize the therapeutic strategy of proton therapy for thoracic malignancies.
Materials/Methods: The experimental animals were 8-week-old C57BL/6 male mice, treated with irradiation (IR) exposure using fixed beam radiation fields along 8 Gy (RBE) proton and 6, 8, 10 Gy photon. Mice were monitored at different time (2 hours, 1 day, 3 days, 1 week and 2 weeks) for changes in serum diagnosis. Cardiac function and toxicity evaluation was completed at 1 week via electrocardiogram, echocardiography, immunofluorescence, H&E and Masson staining. RBE was established as the proton-to-photon dosage ratio when two types of IR produced the same biological output
Results: Serum cTn-I level elevated and peaked at 1 week after proton IR. Compared to photon, higher weight loss and QT interval prolongation were observed in proton arm. Echocardiography revealed a slight reduction of ejection fraction and a much thinner systolic ventricular septum thickness (IVSs) on day 7 after proton IR. H&E staining showed inflammatory infiltrating foci and disordered muscle bundles in ventricular septum in proton IR group compared with the photon group. The recalculated RBEs were 1.375 for TUNEL (+) cells and 1.1 for TGF-ß (+) cells in heart.
Conclusion: Early biological response in cardiac toxicity induced by proton IR exhibits different damage pattern in terms of cardiac function impairment than photon IR. Different cells within heart may have different RBE with proton beam.