A phantom study of internal target volume and mid-position accuracy in adaptive and conventional four-dimensional computed tomography across regular and irregular motion

This technical note evaluates the performance of an adaptive four-dimensional computed tomography (4DCT) acquisition method compared to conventional 4DCT using a motion phantom. Metrics assessed include deviations in volume, CT number, diameter, peak-to-peak amplitude and determination of the internal target volume (ITV) and mid-position. Under regular breathing, most measurements fall within predefined clinical tolerances for all systems. Under irregular motion, the adaptive method showed reduced deviations in ITV and minimal impact on mid-position determination. These findings support the clinical value of adaptive 4DCT in improving motion management and target definition accuracy in radiotherapy planning.