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Objective: Setup verification is the critical part to make sure of the accuracy for Intensity-modulated radiotherapy in nasopharyngeal cancer patients. This pilot study was designed to answer whether and how much the kV-CBCT in addition to 2DkV is more accurate than 2DkV alone in terms of verification parameters.
Methods: Images acquisition: Offline images were displayed in the matched position between reference images. 2D and 3D matches: The bony matches were done by using the location of the tumor in the nasopharyngeal and upper neck regions. The distances displaced from the isocenter were recorded in x-y-z directions. Analysis: The distance of the isocenter shift in each direction (X, Y, Z) were presented as point estimations. The alignment between the two methods was assessed with Pearson’s and Spearman’s correlation. The 3 mm difference within 90% is considered as an acceptable range of non-inferiority of 2DkV, compared with CBCT.
Results: 11 nasopharyngeal cancer patients were included into this study. The correlation between 2DkV and kV-CBCT were 0.46, 0.11 and 0.16 for Superior-inferior (SI), Anterior-posterior (AP) and Left-right (LR) directions, respectively. The central value for the kV-CBCT; SI, AP and LR directional shift were 0.07, 0.06 and 0.03 cm, respectively, whereas the central value
for 2DkV; SI, AP and LR directional shift were 0.05, 0.07 and 0.04 cm. For the difference shift < 3 mm, the results > 90% were within acceptable value: 100% and 96.96% for SI and LR directions whereas the AP direction was 87.87%.
Conclusion: Compared with kV-CBCT by using our criteria, 2DkV images are accurate enough for treatment verification in nasopharyngeal cancer patients.
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