E Mathias*, N Morton, R O'Brien, University of Sydney, Eveleigh, NSWAU,

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  E Mathias

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SU-D-TRACK 4-6 (Sunday, 7/25/2021) 2:00 PM - 3:00 PM [Eastern Time (GMT-4)]

Purpose: 4DCT imaging plays an important role in current 4D radiotherapy treatment planning. Conventional helical 4DCT scans are prone to image artifacts caused by breathing irregularity and the difficulty in satisfying the data sufficiency condition. To reduce image artifacts in helical 4DCT scans, we have developed a prospective couch velocity adaptation and gating protocol, known as REACT that allows an acquisition in a phase-specific displacement gating window and adapts the pitch based on the patient’s breathing.

Methods: Conventional helical 4DCT scans and prospective respiratory gated 4DCT acquisition (REACT helical) were simulated for 10 patients from the Virginia Commonwealth University tumour motion database using the REACT software. The REACT acquisition in helical mode was simulated both with a constant pitch and a variable pitch value which was updated in response to real-time changes in the patient’s breathing rate. An initial training period was used to learn the patient’s breathing characteristics and then to determine potential beam gating. The performance of the scans was measured using trace RMSE during imaging (a surrogate for breathing irregularity and image quality) and beam on time (a surrogate for imaging dose).

Results: As compared to a conventional helical 4DCT, the average breathing irregularity (RMSE) during imaging was reduced by 36.84% and 12.06% for the constant pitch REACT acquisition and the variable pitch REACT acquisition respectively. The average beam on time increased by 49.23% for the variable pitch REACT acquisition as compared to a constant pitch REACT acquisition

Conclusion: The results demonstrate the potential of using the REACT method with an adaptive pitch to reduce image artifacts in helical 4DCT scans. While the gating protocol allows for reduction in breathing irregularity related artifacts, varying pitch allows to close the data sufficiency gap.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Cancer Australia funding (Application Number:1139268)

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