Background: Local computed tomography (CT) reconstruction is achievable with portal images acquired during volumetric-modulated arc therapy (VMAT) delivery and was named as VMAT-CT. However, the application of VMAT-CT is limited because it has limited field of view and no density information. In addition, the new generation of multi-leaf collimator with faster speed and various collimator angles used in patients’ plans could cause more artifacts in VMAT-CT. The goal of this study was to extend VMAT-CT concept, generate complete three-dimensional (3D) CT images, calculate new 3D dose, track and adapt VMAT plan based on updated images and dose. Materials and methods: VMAT-CT and planning CT of phantoms were fused by rigid or deformable registration to create VMAT-CT+ images. Trackings based on planning CT, VMAT-CT+, and cone beam CT (CBCT) were compared. When prescription dose was not met for planning target volume (PTV), re-planning was demonstrated on an in-house deformable phantom. Possible uncertainties were also evaluated. Results: Tracking based on VMAT-CT+ was accurate and superior to those based on planning CT and CBCT since VMAT-CT+ can detect changes during treatment. PTV coverage in the deformable phantom decreased after deformations but went up and met the prescription goal after re-planning. The impact of uncertainties on dose was minimal. Conclusion: 3D tracking and adaptation of VMAT based on VMAT-CT are feasible. Our study has the potential to increase the confidence of beam delivery, catch and remedy errors during VMAT.
Publication Source (Journal or Book title)
Radiotherapy and Oncology
Zhao, X., & Zhang, R. (2020). Feasibility of 3D tracking and adaptation of VMAT based on VMAT-CT. Radiotherapy and Oncology, 149, 18-24. https://doi.org/10.1016/j.radonc.2020.04.032