The design intent of this phantom is to provide a tool that can be used for both electron density calibration and image quality assessment of Cone Beam CT systems integrated in radiation therapy devices. The electron calibration function of the phantom enhances the outcome of the adaptive radiation therapy while the image quality features address the fine balance between optimising image quality while minimising radiation dose.
The 062MQA CBCT Electron Density & Image Quality Phantom consists of several sections: a 100mm thick body slab, a 100 mm thick CBCT Image Quality phantom, a 50mm thick Electron Density Phantom, and a Bolus consisting of a 37.5mm thick uniform slab, a 12.5mm thick uniform slab and a 50mm thick uniform slab.
The 100 mm thick body section has a central hole that receives the CBCT Image Quality Phantom. Each Bolus slab is drilled to accommodate an ion chamber insert and allow for ion chamber measurements regardless of the position of the Image Quality Insert. The thicknesses of the sections were selected to allow for positioning of any of the layers containing the Image Quality features in the central axis of the beam. Also sections of different thickness decrease the increment with which the electron density section can be offset from the central axis.
The phantom support along with laser alignment marks allow for easy and quick positioning of the phantom on the accelerator couch. The phantom is placed on the support rails with the help of machined grooves. Buffer plates are provided to decrease the artifacts from the support device and to allow the user to access the handles on the support plates. The leveling of the support and implicitly the phantom is done by adjusting leveling feet.