Validation of Geometric and Dosimetric Accuracy of Edge Accelerator Gating With Electromagnetic Tracking: A Phantom Study

Abstract

This work was to devise a comprehensive testing scheme to evaluate the geometric and dosimetric accuracy of the Edge accelerator gating with electromagnetic tracking (EMT) for its safety in clinical application. A CIRS thorax phantom was scanned with four-dimensional cone-beam CT (4D-CBCT) on an Edge accelerator while the simulated tumor was simultaneously tracked with an EMT system using Calypso. The geometric accuracy was validated by comparing the motion trajectories derived from Calypso and 4D-CBCT with the ground truth from motion control software. The two-dimensional and three-dimensional dynamic doses were measured with the Matrixx and ArcCHECK installed on a motion platform, both with and without EMT. For tumor motion with 5, 7.5 mm amplitudes, the average absolute differences of sample position between Calypso and the ground truth were 0.286±0.234 mm, 0.407±0.331 mm respectively. Dosimetric accuracy was validated with 3 mm/3% gamma criterion. The average gamma pass rates of 2D dynamic dose validation based on Matrixx were less than 46% without EMT, 97.3% using 2 mm gating limit, 96% using 3 mm gating limit and 93.4% using 5mm gating limit respectively. The mean 3D dynamic dose validation pass rates based on ArcCHECK were 65.9% without EMT, 96.2% using 3 mm gating limit, and 92.5% using 5 mm gating limit with EMT respectively. The geometric accuracy of the Calypso system in tracking the moving target area was stable at the submillimeter level. The dosimetric accuracy could be improved significantly with EMT using an appropriate gating limit.

Keywords

• Radiotherapy
• accuracy
• electromagnetic tracking