Y. Hao1, J. P. Schiff1, J. Shah2, and G. D. Hugo1; 1Washington University School of Medicine in St. Louis, Department of Radiation Oncology, St. Louis, MO, 2Siemens Healthineers, Cary, NC
Purpose/Objective(s): Phantom studies show that intelligent four-dimensional computed tomography (i4DCT) sequence-scanning can reducing breathing irregularity related artifacts significantly comparing to traditional spiral 4DCT, but clinically the two techniques from a single simulation session have not been compared. i4DCT is a sequence scan with beam on times adapted to individual patient breathing pattern in real time to optimize projection data coverage. Here we report quantitative and qualitative evaluations of spiral 4DCT and i4DCT during simulation. Materials/
Methods: Thirty-three patients’ spiral 4DCT and i4DCT were collected retrospectively on an IRB approved study from patients with irregular breathing traces on both 4DCT acquisitions. The irregularities here include irregular breathing amplitude, or irregular frequency, or the combination of both. Spiral 4DCT and i4DCT scans were acquired during a single simulation session. Short spiral 4DCT scans were used for motion evaluation, while the long i4DCT scans used for treatment planning. To compare the internal target volume (ITV) on both 4DCT datasets, a radiation oncologist manually contoured all ITVs de novo on average CTs. Residual sorting artifacts were visually evaluated and scored by a radiation oncologist and medical physicists on a scale of 1 to 3 where score from high to low indicated the presence of artifact around tumor or within tumor, away from tumor, and no substantial artifacts, respectively. Results: The ITVs comparison between two 4DCT techniques revealed mean, standard deviation (STD), maximal, and minimal Dice similarity coefficients of 0.59, 0.18, 0.85, and 0.13 respectively. ITV mean HU difference varies between 0.80 HU to 518.26 HU (Mean±STD: 53.97±92.46 HU). For the spiral 4DCT phases, 30.30%, 48.48%, and 21.21% of patient’s dataset scored at 3, 2, 1, respectively. For these cases scored at 3, artifacts happened within or around tumor on multiple slices, which indicated rescan may necessary. While some of such artifacts diminished on average CT since not all the phases suffering from same artifacts. For i4DCT, none of the phase shows level 3 artifacts. The local rescanning and rebinning further enhance image quality for individual 4DCT phases. Conclusion: Our results show irregular breathing patterns can degrade spiral 4DCT quality and tumor delineation. The novel i4DCT technique provides a reliable solution to reduce such artifacts significantly.
