Four-Dimensional Radiotherapy and Respiratory-Gated Radiotherapy for Lung Cancer

Four-dimensional radiotherapy is defined to add time factor to three-dimensional radiotherapy. In our institution, we have used a four-dimensional computed tomography (4D-CT) and a respiratory-gated radiotherapy system (RPM; Real-time Position Management System) since 2009. The respiratory-gated radiotherapy with this system can improve significant decrease of lung dose in patients with large respiratory motion. On the other hand, this system has not only uncertainties, such as the reproducibility of respiratory motion and target delineation, but also several problems, such as increase of radiation exposure due to 4D-CT scanning, complicated treatment planning and established evidence. We need to solve these problems for the prevalence of respiratory-gated radiotherapy in future.