SU-E-J-161: Quality Assurance of 4DCT Process Using ET Gating Phantom System

Purpose: To develop a robust quality assurance procedure for 4DCT process using ET gating phantom (ET-GPS), to optimize 4DCT scan protocols, and to investigate practical solutions for patients who have difficulties to be scanned with 4DCT. Methods: ET-GPS (BrainLab AB) in conjunction with the marker block is used to test the motion tracking of 4DCT imaging and Real-time Position Management (RPM) system (Varian). Several standard sinusoidal motion profiles as respiratory simulation were used as reference. A maximal motion range of 2.5mm to 16.5mm for horizontal motion (HM) and 6.4mm to 38.0mm for vertical motion (VM), with breathing period time (T) of 3s, 5s, and 7s, were applied to ET-GPS, respectively. 4DCT images were acquired by LightSpeed 16-slice CT simulator (GE Medical System), using our general 4DCT chest imaging protocol (cine, 120kVp, 350mA, 0.8s) with scan thicknesses of 1.25mm and 2.5mm, respectively. Maximal motion ranges obtained from 4DCT imaging were analyzed and compared to the references. Furthermore, acquired trajectory profiles from RPM system were played back to the ETGPS, agreement between 2nd acquired trajectories and reference sinusoidal profiles were analyzed quantitatively. Results: Test results of maximal horizontal motion ranges from 4DCT image agree well with the physical measurement (u003c3%) when the scan thickness is 1.25mm and with T = 5s or 7s. Motion range discrepancy is up to 13.5% for HM when 2.5mm thick is applied. The VM differences are less than 7%. ET-GPS can reproduce the patient motion profiles very well. Conclusion and discussion: The developed method using ET-GPS is a feasible and efficient way for quality assurance of 4DCT process. Imaging protocols can be further optimized when agreement is out of the expected. Further 4DCT QA procedure with different HU inserts and customized patient breathing profile will be investigated.