Effect of gantry speed on accuracy of extracted target motion trajectories and image quality in 4D-CBCT: phantom study

Abstract

Purpose. Four-dimensional cone-beam computed tomography (4D-CBCT) has attracted considerable attention due to requirements for patient motion management devices in stereotactic body radiation therapy. In addition, the determination of relevant parameters, such as gantry speed for 4D-CBCT image acquisition is important in reducing the imaging dose. The purpose of this study was to evaluate the effect of gantry speed on the tumour motion trajectory and image quality using a respiratory motion phantom. Materials and Methods. The tumour (1, 2 and 3 cm) motion trajectories were evaluated to calculate the tumour volume, centroid position, and diameter for a sinusoidal wave pattern and irregular respiratory pattern. The image quality was evaluated based on the standard deviation and contrast-to-noise ratio (CNR) of a 4D-CBCT image. Results. In terms of the tumour motion trajectories, a significant difference existed in the tumour volume and diameter between a gantry speed of 1° s–1 and high gantry speeds of 4, 5 and 6° s–1. Furthermore, the difference variation increased with an increase in the gantry speed. The centroid position of the tumour was within 1.5 mm for all gantry speeds and tumour sizes. For the irregular respiratory pattern, the difference variation in the tumour volume and diameter showed the same tendency as the sinusoidal pattern. The maximum differences of the centroid position were measured in the cases of high gantry speeds of 4, 5 and 6° s–1 for all respiratory motion patterns. With respect to image quality, the CNR was significantly lower when the gantry speed was greater than 4° s–1. Conclusion. A low gantry speed can lead to an increase in the imaging dose, whereas a high gantry speed can reduce the accuracy of the tumour motion trajectory and image quality. In our study, we estimated the appropriate gantry speed to be 3° s–1 for 4D-CBCT.