Purpose: 4D Cone Beam Computed Tomography (4DCBCT) suffers from streak artefacts, long scan times and high imaging doses. We have developed respiratory motion guided (RMG)-4DCBCT that adapts the gantry rotation speed and projection acquisition to real-time changes in the patientâ€™s breathing rate with in-silico studies demonstrating that 60-90s scan times are possible. This study tests the feasibility of this novel method for low dose and short scan-times on a commercial linear accelerator.
Methods: Four respiratory traces representing the mid-quartile in breathing period were selected from 24 lung cancer patients (2-13s range in period). Motion was simulated with a 3D anthropomorphic thorax phantom on a 1D motion stage. The RMG-4DCBCT hardware, installed on an Elekta Synergy linear accelerator, adapted the gantry rotation speed and projection pulse rate in response to the real-time respiratory signal from an optical sensor. Scans were acquired using RMG-4DCBCT with 200, 300 and 400 total projections (20, 30 and 40 projections in each of the 10 phase bins) corresponding to 85%, 77% and 70% imaging dose reductions compared to the 1320 projections with conventional 4DCBCT. Scan time, contrast to noise ratio (CNR) and edge response width (ERW) were used to evaluate image quality and image sharpness.
Results: RMG-4DCBCT was successfully implemented on all respiratory traces. The average scan time for 200, 300 and 400 total projections was 93s, 136s and 158s respectively compared to 240s for conventional 4DCBCT. For the 200, 300 and 400 projection RMG-4DCBCT scans, the CNR was 3.5Â±0.38, 4.5Â±0.3 and 5.4Â±0.4 respectively and the image sharpness, measured by the ERW, was 0.9Â±0.4mm, 0.8Â±0.4mm and 0.7Â±0.2mm respectively.
Conclusion: RMG-4DCBCT with low dose and short scan times is feasible on a range of patient breathing traces and this study has inspired an upcoming clinical trial that will open in mid-2019.
Funding Support, Disclosures, and Conflict of Interest: This research was supported by NHMRC project grant #1138899 and grant #1123068 awarded through the Priority-driven Collaborative Cancer Research Scheme and funded by Cancer Australia. Ricky O'Brien acknowledges the support of a Cancer Institute NSW Career Development fellowship. Paul Keall acknowledges the support of an NHMRC Senior Principal Research Fellowship.
Not Applicable / None Entered.