Accuracy of target volume and artifact reduction by optimal sorting methods of 4DCT image reconstruction on lung cancer radiotherapy in patients with mismatched pitch in irregular respiration
Keywords:
Artifact, Four-dimensional computed tomography, Salvage radiotherapy, Sorting, Tumor volumeAbstract
Backgrounds: In four-dimensional computed tomography (4DCT), pitch estimates are initially selected before data acquisition. However, during data acquisition, it is observed that pitch values mismatch with the breathing period due to respiratory changes, leading to image artifacts. Addressing this issue requires the selection of an appropriate sorting method, especially for a group of patients in such cases who lack a standardized sorting protocol.
Objective: The study aims to determine the optimal 4DCT scan sorting method for patients with a set-up pitch not aligned with breathing period.
Materials and methods: The respiratory waveforms of 40 lung cancer patients were programmed into the CIRS dynamic thorax phantom, and data were acquired using a CT scanner. Subsequently, 4DCT scans were performed, and the appropriateness of the pitch values, which were set according to standard protocols, was assessed. Three sorting methods, namely phase-based, amplitude-based, and percent Pi-based, were evaluated for their impact on volume accuracy, shape, and the presence of artifacts on 4DCT image in terms of absolute volume difference (AVD), sphericity, and artifact score, respectively, specifically in six subjects with inappropriate parameter settings for acquisition data.
Results: Among the 40 patients studied, six respiratory waveforms had improper parameter settings. The volume of a spherical object for the respiratory phases of 0% and 50% showed similarities to the static volume in all three sorting methods, resulting in an AVD range of 0.18-0.29 cm3. The sphericity values of the three sorting methods with phases of 0% and 50% exhibited variations ranging from 0.001 to 0.003, and the artifacts exhibited a severity level close to 2. Therefore, the study recommended using the images at the 0% and 50% respiratory phase with all sorting methods for target contouring images in clinical practice, as they closely matched the static volume. The findings emphasize the importance of aligning pitch values with the breathing period during data acquisition to maintain image quality.
Conclusion: In patients with irregular breathing amplitude and a mismatch in respiratory rate and breathing period, phase-based or percent Pi-based sorting methods were preferably used for 4DCT reconstructions.
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