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Residual Set Up Errors of the Surrogate-guided Registration Using Four-dimensional CT Images and Breath Holding Ones
Yoshihiro Ueda1, Mari Tsujii2, Shingo Ohira2
1Department of Radiation Oncology, Osaka International Cancer Institute, Osaka, Japan; uedetu@gmail.com.
Background/Aim:
To evaluate the surrogate-guided registration accuracy of two computed tomography (CT) image sets, expiratory phase four-dimensional (Ex4D) CT and breath-holding CT (BHCT), in respiratory-gated radiotherapy for liver cancer.
Materials And Methods:
The surrogate-guided registration errors were defined as the differences between the diaphragm- and fiducial-guided registrations or the differences between upper and lower fiducial registrations in three directions: left-right (LR), anterior-posterior (AP), and cranio-caudal (CC).
Results:
The mean±SDs of the absolute errors for diaphragm-guided registration were 1.9±1.3, 2.7±1.8, and 2.6±1.7 mm with Ex4D and 1.8±1.8, 2.6±1.9, and 1.8±1.7 mm with BHCT in the LR, AP and CC directions, respectively (CC direction, p<0.01). In the fiducial-guided registration, there were no significant differences in any direction. In registration with Ex4D, there were positive correlations between registration errors and the respiratory irregularity during 4D scanning (correlation coefficient; diaphragm: 0.65, fiducial: 0.54).
Conclusion:
BHCT has the advantage of accurate surrogate-guided registration compared with Ex4D.
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