Review of the Medical Physics and Engineering Conference 2019 Poster presentation by Geraldine Verschoor, Nikolaos Margellos, and Will Holmes Smith of Norfolk and Norwich University Hospitals, Norwich, UK. The MPEC 2019 Conference was held in Bristol, UK, in late 2019, and was sponsored by the Institute of Physics and Engineering in Medicine.
Treatment with radiation on a modern linear accelerator relies on the ability to position the patient with incredible accuracy. Therefore it is critically important to verify that the systems used for positioning are all describing the same isocentric point in space as the treatment beam. Treatment couches with 6 degrees of freedom (6DoF) can add additional uncertainty to this system.
The Standard Imaging MIMI (Multiple Imaging Modality Isocentricity) Phantom establishes mechanical stability of the image guidance system by verifying the isocentre described by the MV, kV, CBCT, and other guidance systems is within accepted 1mm tolerances. HexaCheck is an accessory to the MIMI Phantom that allows isocentre rotation using a gimbal system along all three axes of rotation (roll, pitch, yaw) in ±2.5° increments. The gimbal ensures the centre of the phantom will remain at isocentre when there is a rotational offset. This greatly simplifies data analysis and enables commissioning and verification of 6D couch alignment and positioning offsets in a busy clinical environment without the need to write extra software.
In 2018 and 2019, the NNUH commissioned two Varian TrueBeam Linear Accelerators (Linacs) each with a 6DoF couch and reported the following independent study results using the MIMI/HexaCheck to assist with commissioning: