Purpose: Recently our centre purchased an Elekta-Synergy accelerator with kV-CBCT and a hexapod couch attachment. This system allows six degrees of freedom for couch top shifts, based on registration of on line imaging. We designed and built a phantom in our centre to test the accuracy and precision of this system. The goal of this project was to investigate the accuracy and practical utilisation of this phantom.
Method: The phantom was constructed from perspex sheets and high density dental putty (Fig1). Five high density regions (three small regions to simulate prostate seeds and two larger regions to simulate boney anatomy) were incorporated to test the manual and automatic registrations within the software. The phantom was utilised to test the accuracy and precision of repositioning with the hexapod couch and imaging system. To achieve this, the phantom was placed on the couch at known orientations and the shifts were quantified using the registration of verification and reference image data sets. True shifts and those predicted by the software were compared.
Results: The geometrical accuracy of the phantom was verified with measurements of the CT scan to be with 1 mm of the intended geometry. The image registration and resultant couch shifts were found to be accurate within 1 mm and 0.5 degrees. The phantom was found to be practical and easy to use.
Conclusion: The presented phantom provides a less expensive and effective alternative to commercially available systems for verifying imaging registration and corresponding six degrees of freedom couch shifts.