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The HexaCheck and MIMI Phantom: Norfolk and Norwich preferred choice for weekly 6 DOF couch QA.

Image guided radiotherapy (IGRT) has become the most prominent form of patient setup correction and verification in radiotherapy. State of the art treatment delivery systems commonly incorporate 6DoF couches able to correct for rotational errors in all three directions along with translational corrections.

HexaCheck answers demands for accuracy in all six dimensions by providing a precise and consistent method for performing both 6D couch commissioning and QA. The phantom holder is secured into the couch for isocenter alignment, while locking mechanisms for offset angles ensure accuracy every time.

Will Holmes-Smith, Lead Clinical Scientist (QA & Machine Dosimetry) at Norfolk and Norwich University Hospitals describes his experience with the HexaCheck: He explains, “We actually have three of the HexaCheck and MIMI phantoms in the department (one for each linac that has a 6DoF couch). We use them for weekly 6DoF couch QA. Whilst there were other solutions to doing QA for a 6DoF couch we felt that this was the best option as you are able to produce random shifts and rotations using the phantom to test the system, the test is not restricted to a set of movements, so the random and systematic errors in the system are checked.”

The HexaCheck has been designed to integrate with the MIMI Multiple Imaging Modality Isocentricity Phantom. The MIMI ensures image guidance accuracy by measuring the coincidence of isocenter prescribed by the lasers, treatment beam and image guidance systems. Five bone equivalent rods intersect at 90 degree angles for easy alignment and automatic registration. These rods are visible in any image or slice for automatic registration of 2D/2D and 3D/3D matching and verification of isocenter position. Fast and accurate alignment checks are established with mechanical stability of an image guidance system by verifying isocenter within 1 mm. A 6.4 mm sphere at the centre of the phantom assists with virtual and physical graticule alignment checks.

The advantage of the HexaCheck-MIMI phantom is the centre of the phantom will remain at isocentre when there is a rotational offset. This greatly simplifies data analysis and enables commissioning and QA in a busy clinical environment without the need to write extra software.

The HexaCheck fits seamlessly into your workflow as an extension of your 3D IGRT QA routine.

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