A 4DRT simulation study using a synthetic 3.5D CT image with motion-free target of lung cancer based on 4DCT

Four-Dimensional Radiotherapy (4DRT) planning based on 4D Computed Tomography (4DCT) is limited by drastically increased planning workload and unavoidably needed new software. We introduced a new concept of 3.5DCT for a simplified 4DRT planning. This 3.5DCT is synthesised from 4DCT by aligning the tumour centres in each phase, simulating a motion-compensated tumour from the beam eye’s view. Four patients’ 4DCTs were used for the 4DRT planning, which were compared with motion-trajectory-based and respiratory-gated plans. This simplified 4DRT plan shows dosimetric advantage of significant reduction of V95 and V20. This suggests that the static 3.5DCT image is sufficient for 4DRT planning.