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Phase-Matched Digital Tomosynthesis (DTS) Imaging for Simultaneous Target Verification During Volumetric Modulated Arc Therapy (VMAT) Treatment

Y Zhang

Y Zhang*, L Ren, I Vergalasova, J Cai, F Yin, Duke University, DURHAM, NC

TU-A-BRA-9 Tuesday 8:00:00 AM - 9:55:00 AM Room: Ballroom A

To develop a phase-matched DTS technique to allow tomographic verification of moving targets simultaneous to VMAT delivery

This study proposes to verify moving targets by comparing phase-matched reference DTS (Ref-DTS) generated from simulation 4DCT to corresponding on-board DTS (OBI-DTS) acquired during VMAT delivery.

The 4D Digital Extended Cardiac Torso (XCAT) Phantom was used for demonstration. A normal patient breathing pattern was input into the XCAT phantom to generate on-board CBCT projections, simulation 4DCT, average intensity projection (AIP) of the 4DCT and free-breathing CT (FBCT).

These simulation CT sets (FBCT, AIP and 4DCT) were used to project digitally reconstructed radiographs (DRRs): DRR-FBCT and DRR-AIP (both with no respiratory phase information), and DRR-4DCT matched to phases of on-board projections. These DRR sets were further used to reconstruct three Ref-DTS sets: Ref-DTS-FBCT, Ref-DTS-AIP, and phase-matched Ref-DTS-4DCT. Each Ref-DTS set was compared with OBI-DTS (generated from on-board projections) to identify relative differences between both.

To quantitatively assess the feasibility of comparing each Ref-DTS set with OBI-DTS for target verification, the simulation CT sets were shifted by a given amount to simulate target motion/setup variation, and the resulting Ref-DTS sets were registered to OBI-DTS automatically. The accuracy of target verification was evaluated by the discrepancies between simulated and registered shifts.

For a 1mm discrepancy criterion between simulated and registered shifts, the success rates between OBI-DTS /Ref-DTS-FBCT, OBI-DTS /Ref-DTS-AIP, and OBI-DTS /Ref-DTS-4DCT registrations are 14.3%, 28.6%, and 100% for 2mm shifts, 0%, 14.3%, 100% for 5mm shifts, and 42.9%, 28.6%, 100% for 10mm shifts, respectively.

The simulation study indicated that the phase-matched Ref-DTS-4DCT technique considerably improved the target verification accuracy than that provided by non-phase-information Ref-DTS-FBCT or Ref-DTS-AIP. Therefore, it has the potential to validate VMAT treatment of moving targets.

(Research partially supported by grant from Varian Medical Systems)

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