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Objective To investigate the impact of anatomical landmarks on registration in image?guided radiotherapy (IGRT) for central and peripheral lung cancer. Methods Twenty?five patients with central or peripheral lung cancer for IGRT were enrolled in this study. Kilo?voltage cone?beam CT ( kV?CBCT) scanning was acquired before irradiotion. Tumor coverage on CBCT was assessed using gross tumor volume (GTV), clinical target volume (CTV), and planning target volume (PTV) contours according to tumor alignment, carina registration, and spine registration, respectively. The grading analysiswas based on visual tumor assessment as follows:grade 0, tumor within GTV;grade 1, tumor outside GTV but inside CTV;grade 2, tumor outside CTV but inside PTV;and grade 3, tumor outside PTV. Results Totally 177 sets of kV?CBCT of 25 patients was collected. According to the registration landmarks of the tumor, carina and spine for central lung cancer, the percentages were 57?55%, 53?77% and 16?04% in grade 0, 39?62%, 45?28%and 58?49% in grade 1, and 1?89%, 0?94% and 25?47% in grade 2, respectively. For peripheral lung cancer, the percentages were 47?89%, 14?08% and 2?82% in grade 0, 43?66%, 29?58% and 45?07% in grade 1, and 8?45%, 40?85% and 35?21% in grade 2, respectively. Conclusions For central lung cancer,the tumor was recommended as the best registration landmark, and the carina was recommended as well, while the spine was not recommended. For peripheral lung cancer, the tumor was recommended as the best registration landmark, while the spine and the carina were not recommended.
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Objective To analyze artifacts of gross tumor volume (GTV) and correlated factors in each phase images of four dimensional CT (4DCT) for peripheral lung cancer based on three dimensional CT (3DCT) assisted with active breathing control.Methods Nineteen patients with peripheral lung cancer underwent 3DCT (CTFB) and 4DCT simulation scans during free breathing and then underwent 3DCT simulation scans in end inspiration hold (CTEIH) and end expiration hold (CTEEH) assisted with active breathing control.The relative deviations (Devref) between the reference GTV (GTVref) and the GTVsdelineated based on CTFB (GTVFB) and all phases of 4DCT were calculated respectively.Correlations between GTVref and Devmax and between the tumor motion in the cranio-caudal (CC) direction and Devref were analyzed.Results The maximum median Devref of GTV was GTVFB with 17.83％,and the maximum median Devref of the GTV in all phases of 4DCT was GTV30 with 17.20％.A significant negative correlation was found between GTVEIH and Devmax (r =-0.691,P =0.001).The Devref was crrnelated with the tumor motion amplitude in the CC direction (r =0.323-0.617,P =0.005-0.150).The partial regression coefficient of influence of GTVref size and motion amplitude in the CC direction to the tumor Devmax were -0.500 and 0.583,P =0.002 and 0.001,respectively.Conclusions The GTV artifacts in different phase of 4DCT for the peripheral lung cancer were different to each other,and the influence of target displacement to artifacts was larger than that of target volume,so artifacts could be reduced by controlling breathing to reduce target displacement.