Influence of Acquisition Mode of Cone-beam Computed Tomography on Accuracy of Image Registration for Image-guided Radiotherapy

Abstract

Half scan can acquire images at the 200 degrees rotation in image-guided radiation treatment using cone-beam CT and is useful to evaluate the influence of the half-scan-imaging start angle and imaging direction on image registration accuracy. The half-scan-imaging start angle is changed from 180 degrees to 340 degrees in the clockwise direction and from 180 degrees to 20 degrees in the counter clockwise direction to calculate the registration error. As a result, registration errors between -0.37 mm and 0.27 mm in the left and right directions occur because of the difference in the imaging start angle and approximately 0.3 degrees in the gantry rotation direction because of the difference in the imaging direction. Because half scan does not have data for 360 degrees rotation, depending on the subject structure, inconsistency of opposing data can lower reconstruction accuracy and cause a verification error. In addition, in image acquisition during rotation, the slower the shutter speed is, the more the actual gantry angle and angle information of the image are apart, which is considered the cause of rotation errors. Although these errors are very minute, it is thought that there is no influence on the treatment effect, but these errors are considered an evaluation item indispensable for ensuring the accuracy of high-precision radiation treatment. In addition, these errors need to be considered for ensuring the quality of high-precision radiation treatment.