| Summary: | Abstract Background To compare the accuracy, advantages and disadvantages of automatic registration methods at different anatomical-sites for thoracic image-guided radiation therapy (IGRT). Methods The Varian-IX IGRT system was used to perform a manual registration of the images collected on the first fraction of 60 patients with lung cancer (42 cases central location and 18 cases of peripheral). The registered images were used as reference images. Offline registration was performed for computed tomography-CBCT images using four methods: whole image registration, ipsilateral registration, soft tissue tumor registration, and vertebral body registration. Time taken to complete and deviation value were analyzed between the different methods. Results There were significant differences in absolute deviation value of all the three directions (P < 0.001) and the time consumption (P < 0.001) between 4 methods. The Z direction had significant differences in deviation value of 4 methods (0.023 ± 0.128 mm, − 0.030 ± 0.175 mm, − 0.010 ± 0.238 mm, − 0.075 ± 0.137 mm, P = 0.011). The difference was significant in the X direction of the ipsilateral registration method between central and peripheral lung cancer (0.033 ± 0.053 mm vs. 0.067 ± 0.067 mm, P = 0.045). Conclusions The whole lung or affected side registration methods could be recommended to be used in the automatic registration function of the Varian-IX’s On-Board Imaging (OBI) system.
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