MO‐AB‐BRA‐09: Development and Evaluation of a Biomechanical Modeling‐Assisted CBCT Reconstruction Technique (Bio‐Recon)

Abstract

Purpose:To develop a Bio‐recon technique by incorporating the biomechanical properties of anatomical structures into the deformation‐based CBCT reconstruction process.Methods:Bio‐recon reconstructs the CBCT by deforming a prior high‐quality CT/CBCT using a deformation‐vector‐field (DVF). The DVF is solved through two alternating steps: 2D–3D deformation and finite‐element‐analysis based biomechanical modeling. 2D–3D deformation optimizes the DVF through an ‘intensity‐driven’ approach, which updates the DVF to minimize intensity mismatches between the acquired projections and the simulated projections from the deformed CBCT. In contrast, biomechanical modeling optimizes the DVF through a ‘biomechanical‐feature‐driven’ approach, which updates the DVF based on the biophysical properties of anatomical structures. In general, Biorecon extracts the 2D–3D deformation‐optimized DVF at high‐contrast structure boundaries, and uses it as the boundary condition to drive biomechanical modeling to optimize the overall DVF, especially at low‐contrast regions. The optimized DVF is fed back into the 2D–3D deformation for further optimization, which forms an iterative loop. The efficacy of Bio‐recon was evaluated on 11 lung patient cases, each with a prior CT and a new CT. Cone‐beam projections were generated from the new CTs to reconstruct CBCTs, which were compared with the original new CTs for evaluation. 872 anatomical landmarks were also manually identified by a clinician on both the prior and new CTs to track the lung motion, which was used to evaluate the DVF accuracy.Results:Using 10 projections for reconstruction, the average (± s.d.) relative errors of reconstructed CBCTs by the clinical FDK technique, the 2D–3D deformation‐only technique and Bio‐recon were 46.5±5.9%, 12.0±2.3% and 10.4±1.3%, respectively. The average residual errors of DVF‐tracked landmark motion by the 2D–3D deformation‐only technique and Bio‐recon were 5.6±4.3mm and 3.1±2.4mm, respectively.Conclusion:Bio‐recon improved accuracy for both the reconstructed CBCT and the DVF. The accurate DVF can benefit multiple clinical practices, such as image‐guided adaptive radiotherapy.We acknowledge funding support from the American Cancer Society (RSG‐13‐326‐01‐CCE), from the US National Institutes of Health (R01 EB020366), and from the Cancer Prevention and Research Institute of Texas (RP130109).