Risk of Radiation-Induced Second Primary Cancers and Cardiotoxicity following Therapeutic Irradiation for Thymoma with Photon Beams: A Treatment Planning Study

This study compared the risks for developing second primary cancers and cardiotoxicity following radiotherapy for thymoma. Three different 3D-CRT, IMRT, and VMAT plans were generated with 6 MV photons for 12 females with thymoma. Dose-volume histogram data were employed to estimate the second cancer risks using a mechanistic non-linear model. The radiation doses to the heart and cardiac substructures were combined with linear models to assess the probability of cardiotoxicity. The mean lifetime risk for lung, esophageal, thyroid, left breast, and right breast cancer induction was 4.34–4.49%, 0.30–0.31%, 0.05–0.07%, 2.06–2.30%, and 2.04–2.34%, respectively, depending upon the radiotherapy technique. The relative risk for major cardiac events, including myocardial infarction, coronary revascularization, and death, was 1.43–1.55, whereas that for chronic heart failure was 1.20–1.29. The IMRT and VMAT significantly reduced the risk for cardiotoxicity with respect to 3D-CRT (p ≤ 0.023). Small but significant reductions were observed for most organ-specific cancer risks with IMRT compared to conformal treatment (p ≤ 0.008). Similar decreases were detected only for esophageal and thyroid cancer with VMAT (p ≤ 0.033). No difference was found in the probability for radiation-induced lung cancer with the three techniques (p ≥ 0.06). Healthcare professionals may use these data to select the appropriate radiotherapy technique and restrict the risk of late effects.