Purpose: To develop a phase‐matched DTS technique to allow tomographic verification of moving targets simultaneous to VMAT delivery. Methods: 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 onboard 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. Results: 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. Conclusions: 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) Research partially supported by grant from Varian Medical Systems.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging