Can Gating Percentiles Selected From the Phase-Based Planning 4DCT Be Applied for Amplitude-Gated Treatments?
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PO-GePV-M-101 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To compare the motion estimation between the phase-based binning and amplitude-based binning in 4DCT and evaluate if the percentile selected in the phase-based 4DCT is reliable for the gated treatment.
Methods: Both phantom and patient data were used for this study. In the phantom study, 4DCTs were acquired under a regular sinusoidal trajectory and an irregular trajectory with varying periods and amplitudes. A total of 17 patients, including nine with large motion (peak-to-peak magnitude > 12 mm) and eight with moderate motion (peak-to-peak magnitude, 6~12 mm), were included. All 4DCT scans were acquired at Philips CT Big Bore with the pitch of 0.079 using the abdominal respiratory sensor belt. Utilizing an in-house Matlab program, the known target position (KTP) in the phantom scans and the live dome position (LDP) in the patient scans were automatically measured, and the position shifts relative to the base frame (zero percentile) were calculated.
Results: In the phantom experiment with a regular trajectory, we confirmed that the KTP shifts showed a sinusoidal waveform in the phase-based 4DCT and a linear shape in the amplitude-based 4DCT. With the irregular trajectory, three large KTP shifts were underestimated in the amplitude-based phantom 4DCT when compare to phase-based phantom 4DCT, indicating the shift was more accurately measured with the phase-based 4DCT than the amplitude-based 4DCT. For patients with large and moderate respiratory motions, the LDP shifts measured in the amplitude-based 4DCT were smaller in 8 out 10 frames than those obtained in the phase-based 4DCT, consistent with the findings in the phantom experiments.
Conclusion: The percentiles selected from the phase-based planning 4DCT may not be directly applied to amplitude-gated treatments, especially for the patients with large and irregular respiratory motions.
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