A Comprehensive Quality Assurance Procedure for 4DCT Commissioning
Presentations
PO-GePV-M-97 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
ePoster Forums
Purpose: Currently there are no established guidelines to describe and assess the characteristics of a 4DCT system’s performance. We propose a QA protocol for 4DCT commissioning to assess mechanical and computational performance, with phase and normalized-amplitude-based reconstructions, for regular and irregular respiratory patterns.
Methods: The Canon/Aquillion/Exceed/LB scanner interfaced with an Anzai system for motion tracking was commissioned. Test respiratory patterns were provided by the Quasar motion phantom. The target was a 2.0cm diameter sphere. For regular breathing, the motion amplitude was 2.8cm and various pitches were evaluated. For the irregular pattern, 4 scans were performed at various pitches; respiratory patterns were similar in their breathing rate and amplitude variability (averaged over all scenarios, period 4.25s, amplitude range 1.4-2.4cm).The QA procedure encompassed: (1) breathing motion characteristics (period, amplitude) transfer from motion detection system to CT; (2) imaged target accuracy for volume, shape (i.e. elongation along motion direction), and COM amplitude. Geometrical accuracy was assessed against the theoretical values. The results were evaluated for diameter tolerances of half and full reconstructed slice thickness.
Results: The target was accurately captured during regular breathing, regardless of pitch. For irregular breathing, the measured ITV exceeded the nominal geometrical ITV in all scenarios, but all were within our tightest tolerance except for one pitch setting. Phase and normalized amplitude binning performed similarly.
Conclusion: The regular breathing tests confirmed that the overall system captured the expected motion without significant geometric inaccuracies. The irregular breathing data suggests that the system may be expected to capture in excess the target motion, but the deviation is expected to be within the slice thickness; a margin to account for the 4D acquisition inaccuracies does not seem necessary with the system tested. The pitch did not seem to detrimentally affect any of the ITV geometrical characteristics that have been quantified.
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