ABSTRACT
Objective:To compare the comprehensive performance of three Varian on-board image (OBI) image systems (KV-CBCT, KV-planar and MV-EPID) and to explore the value of the combined application of these three systems in daily image-guided radiotherapy for nasopharyngeal cancer.Methods:KV-CBCT, KV-planar and MV-EPID scanning and registration were carried out in the left and right/abdominal and back/head and foot direction on human head and neck phantom. The set-up error, registration time, additional radiation dose and image quality of the three systems were compared by F-test.Results:KV-CBCT, kV-planar and MV-EPID were scanned for 55 times, respectively, and the set-up errors in the left and right/abdominal and back/head and foot direction of the three image-guided systems were (0.00±5.43)/(-0.02±5.49)/(0.02±5.58) mm, (0.04±5.49)/(0.02±5.56)/(0.02±5.54) mm, (0.02±5.22)/(0.11±5.34)/(-0.04±5.33) mm, respectively ( P=0.999, 1.000, 0.989). The average time consuming was (200±45) s, (120±36) s and (115±42) s; the additional radiation dose from low to high was kV-planar, KV-CBCT and MV-EPID; the image quality from low to high was MV-EPID, kV-planar and KV-CBCT. Conclusions:Three image-guided systems can meet the requirements of image-guided radiotherapy for nasopharyngeal cancer. Based on the overall performance of the three systems, 1 CBCT+ 4 kV planar per week is recommended and EPID should be used as a backup system in daily image-guided radiotherapy for nasopharyngeal cancer. This scheme makes full use of the high image quality of CBCT and the low radiation of kV planar to realize the regular detection of nasopharyngeal cancer volume change and the implementation of high-precision radiotherapy.