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Validation of Slow CT and Comparison to Retrospective 4DCT for Motion Assessment

C Geraghty

C Geraghty1*, J Burch2 , B Hasson1 , L Myers2 , (1) Anne Arundel Medical Center, Annapolis, MD, (2) Versant Medical Physics, Kalamazoo, MI


TU-RPM-GePD-J(A)-5 (Tuesday, August 1, 2017) 3:45 PM - 4:15 PM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: To evaluate and implement a slow CT technique for motion assessment. To evaluate performance using a respiratory phantom and compare to retrospective 4DCT.

Methods: The Standard Imaging Respiratory Gating Platform with the Standard Imaging IMRT Lung Phantom was scanned with no motion activated. The lung inhomogeneity diameter was verified on CT and with direct measurement as 2.9cm in the sup-inf direction. 4DCT scans were acquired on a GE PETCT scanner at varying amplitudes (0.5-2cm) and periods (3-6sec) of lung phantom motion. Cine data was binned into ten phases. Target motion amplitude was measured on 4DCT motion videos with a digital scale. MIP and AveIP data sets were exported to the Eclipse TPS. The phantom was scanned with a slow CT technique on a Siemens Sensation 64 at the same amplitudes and periods of lung phantom motion. Slow CT scans were acquired five times. Differing numbers of slow CT scans were averaged. Sup-inf target motion amplitude was measured on averaged slow CTs.

Results: Sup-inf target motion measured on 4DCT was accurate within 1mm for all periods and amplitudes of lung phantom motion scanned. For all combinations of phantom amplitude and period except 2cm/6sec, sup-inf target motion measured on four averaged CTs was within 1mm of that measured on 4DCT. At 2cm/6sec, the measured sup-inf target motion was within 2mm of that measured on 4DCT. At 0.5cm amplitude, 2 averaged CTs yielded target motions within 1mm of expected results.

Conclusion: A slow CT technique was created that yields motion assessments that agree with 4DCT for a range of target motions. The technique involved averaging four slow CT scans. The averaged slow CT scans had an appearance similar to 4DCT AveIP data sets. This slow CT technique promises accurate motion assessments at lower imaging dose than retrospective 4DCT.

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