RESUMO
Objective To explore the setup error and area registration error during lung cancer radiotherapy by using the on board imager (OBI) of the linear accelerator. Methods Totally 50 lung cancer patients underwent image-guided radiation therapy. Then OBI system was used for the scan validation by electronic portal imaging device (EPID) and cone beam CT (CBCT), and comparative analysis was executed on the setup errors of EPID and CBCT. Results The translation errors of EPID were (-1.62 ±1.58), (2.12 ±1.49) and (4.52 ±2.42)mm respectively at Lat, Vrt and Lng directions, while those of CBCT were (-1.27±1.25), (1.43±1.57) and (3.12±2.62) mm respectively. The registration errors at Lat, Vrt and Lng directions and rotation angle of lung tissue were (-1.27±1.25), (1.43±1.57), (3.12±2.62)mm and (0.5±1.6)° respectively, and those of target area were (-1.56±1.78), (1.68±2.39), (3.42±2.73)mm and (0.8±1.9)° respectively. CBCT and EPID had statistical differences (P<0.05) in setup error validation as well as setup errors at Vrt and Lng directions. There were no significant differences (P>0.05) when CBCT self-registration was involved in selecting different areas. Conclusion CBCT and EPID can both used for the setup validation of lung cancer, while the former behaved better than the latter.