Comparative evaluation of 4DCT and 4DCBCT for motion and volume measurement accuracy in a dynamic phantom

4DCBCT within clinical workflow provides comparable motion and volume measurement accuracy to 4DCT. 3DCBCT estimated motion amplitude showed large differences from the programmed amplitude. 4DCBCT offers explicit and confident motion resolution, and phase-dependent target volume at the time of treatment. These findings support the feasibility of integration of 4DCBCT, pending clinical validation, for image guidance in lung SBRT, especially where motion consistency between simulation and treatment is uncertain. Patient studies are needed to capture the influence of patient-specific breathing irregularities such as hysteresis, baseline drift or anatomical deformation.