A clinical evaluation of spiral 4DCT and intelligent 4DCT sequence scanning

Accurate 4DCT imaging is essential for radiotherapy planning but is often degraded by breathing irregularities. Phantom studies show that intelligent four-dimensional computed tomography (Direct i4D) sequence scanning can significantly reduce artifacts related to breathing irregularity compared to traditional spiral 4DCT. Direct i4D is a sequence-based acquisition mode in which beam-on time is adapted in real time to an individual patient's breathing pattern to optimize projection data coverage. In this study, we compared Direct i4D and spiral 4DCT scan image quality between Direct i4D and spiral 4DCT in a paired design, with both scans acquired for the same patient during a single simulation session. Spiral 4DCT and Direct i4D scans from 33 patients with pre-identified irregular breathing patterns were collected retrospectively. Breathing irregularities included variations in amplitude, frequency, or both. Spiral 4DCT scans were used for motion evaluation, while the Direct i4D scans were acquired for treatment planning. To compare the internal target volume (ITV) on both 4DCT datasets, a radiation oncologist manually contoured all ITVs de novo. Residual sorting artifacts were visually evaluated and scored by a radiation oncologist and medical physicist on a scale of 1 to 5 (where higher scores indicate lower presence of artifacts and better image quality). Visual evaluation of 4DCT phases showed that 36% of spiral 4DCT and 3% of Direct i4D scans would require resimulation. Meanwhile, 18% and of spiral 4DCT and 27% of Direct i4D scans were artifact-free (p-value < 0.1). The ITV comparison between the 2 4DCT techniques revealed mean and standard deviation (STD) Dice similarity coefficients of 0.59 and 0.18, respectively. ITV mean CT value difference varies between 0.80 HU and 158.41 HU (Mean ± STD: 39.41HU ± 40.02 HU). Real-time adaptation of the scan time and rebinning by Direct i4D enhanced the image quality for individual 4DCT phases. Irregular breathing patterns can degrade spiral 4DCT image quality and tumor delineation. The novel Direct i4D technique provides a reliable solution to reduce such artifacts significantly.