Purpose: The unique gimbal system of the BrainLAB Vero allows the treatment head to pivot in two dimensions for tumor tracking. In order to utilize this feature, it is crucial to directly monitor tumor motion during treatment. We present a 3D tumor motion monitoring method incorporating the orthogonal kV imaging subsystems on Vero. Methods: An anthropomorphic phantom was used in this study. A lung tumor and two BBs were driven in a regular 3D sine motion pattern using a programmable 4D motion platform. 4D CT scans were performed and the tumor was contoured at the end of inhale phase. Stereoscopic kV images were acquired at a rate of 5 fps. A spherical template was created to match the projections of BBs. Two sets of DRRs were created: one DRR set containing the tumor only and the other set containing the full anatomy without the tumor. They were combined to produce composite DRRs and their individual positions were optimized by comparing of the composite DRRs with acquired kV images. 3D tumor and BB positions were then determined from the results of stereo kV x‐rays. Results: Dual orthogonal kV images were acquired with the MV beam at gantry angles of 0 and 45 degrees. This produced approximately 640 images with corresponding kV imaging angles of ‐ 315, 45, 0, and 90 degrees. The tumor and the BBs were identified on every kV image. Both 2D and 3D positions were compared with the programmed positions. The maximum differences were 1 mm. Conclusion: The dual kV imaging systems on Vero, used in conjunction with our tumor tracking algorithm, are capable of marker or marker‐less lung tumor tracking. This technique may be applied to track tumors in real‐time to provide direct tumor motion information for compensation of tumor motion throughout the course of radiotherapy.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging