Optimal radiotherapy modality sparing for cardiac valves in left-sided breast cancer

BACKGROUND: The cardiotoxicity caused by radiotherapy is a critical problem in the treatment of patients with breast cancer. The appropriate radiotherapy modality sparing for cardiac valves in left-sided breast cancer has not been well defined. The aim of this study was thus to compare the dosimetric differences in heart and cardiac valves of 3-dimensional conformal radiotherapy (3D-CRT), fixed-field intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT) to find the optimal radiotherapy modality sparing for cardiac valves in patients with left breast cancer. METHODS: From January 5, 2021, to March 15, 2021, 21 patients with left-sided breast cancer postmastectomy were included in this study, and 3 different plans for adjuvant radiation were created using 3D-CRT, IMRT, and VMAT for each patient. All patients received 50 Gy in 25 fractions. The mean dose (D(mean)) of the heart; percentage volume of the heart receiving ≥5 Gy (V(5)), ≥30 Gy (V(30)), and ≥40 Gy (V(40)); and the D(mean) and the near-maximum dose (D(0.03cc)) of cardiac valves were extracted from dose-volume histograms (DVHs) and compared. The correlations in dosimetric factors between cardiac valves and the whole heart were analyzed. RESULTS: IMRT significantly decreased the values of V(5), V(30), V(40), and D(mean) in the whole heart compared to 3D-CRT and VMAT (P<0.001). Among the 3 different plans, IMRT had the lowest radiation dose to the D(mean) and the D(0.03cc) of the aortic valve (1.27 Gy/1.75 Gy), pulmonary valve (3.44 Gy/6.89 Gy), tricuspid valve (1.02 Gy/1.14 Gy), and mitral valve (0.93 Gy/1.00 Gy). Pearson correlation analysis found that local parameters (D(mean) and D(0.03cc)) within valves were strongly correlated to the global parameters (V(5), V(30), V(40), and D(mean)) of the heart. CONCLUSIONS: This study revealed that IMRT showed the lowest cardiac valves dose compared with 3D-CRT and VMAT in left-sided breast cancer radiotherapy. IMRT might be the optimal modality sparing for cardiac valves in this group of patients. Further studies need to be carried out in order to validate the protective role of IMRT on the cardiac valves.