Dosimetric comparison between modulated arc therapy and static intensity modulated radiotherapy in thoracic esophageal cancer: a single institutional experience

PURPOSE: The objective of this study was to compare dosimetric characteristics of three-dimensional conformal radiotherapy (3D-CRT) and two types of intensity-modulated radiotherapy (IMRT) which are step-and-shoot intensity modulated radiotherapy (s-IMRT) and modulated arc therapy (mARC) for thoracic esophageal cancer and analyze whether IMRT could reduce organ-at-risk (OAR) dose. MATERIALS AND METHODS: We performed 3D-CRT, s-IMRT, and mARC planning for ten patients with thoracic esophageal cancer. The dose-volume histogram for each plan was extracted and the mean dose and clinically significant parameters were analyzed. RESULTS: Analysis of target coverage showed that the conformity index (CI) and conformation number (CN) in mARC were superior to the other two plans (CI, p = 0.050; CN, p = 0.042). For the comparison of OAR, lung V(5) was lowest in s-IMRT, followed by 3D-CRT, and mARC (p = 0.033). s-IMRT and mARC had lower values than 3D-CRT for heart V(30) (p = 0.039), V(40) (p = 0.040), and V(50) (p = 0.032). CONCLUSION: Effective conservation of the lung and heart in thoracic esophageal cancer could be expected when using s-IMRT. The mARC was lower in lung V(10), V(20), and V(30) than in 3D-CRT, but could not be proven superior in lung V(5). In conclusion, low-dose exposure to the lung and heart were expected to be lower in s-IMRT, reducing complications such as radiation pneumonitis or heart-related toxicities.