Norfolk and Norwich trust chooses HexaCheck for couch QA

Designed for the MIMI (multiple imaging modality isocentricity) phantom, HexaCheck allows secure integration with the phantom to make it simple to perform 6D couch commissioning and QA in image-guided radiotherapy.

Treatment delivery systems commonly incorporate 6DoF (six degrees of freedom) couches able to correct for rotational errors in all three directions along with translational corrections. HexaCheck provides a precise method for performing 6D couch commissioning and QA, says UK distributor Oncology Imaging Systems (OIS). The phantom holder is secured into the couch for isocentre alignment, while locking mechanisms for offset angles ensure accuracy every time.

Norfolk and Norwich University Hospitals NHS Foundation Trust lead clinical scientist for QA and machine dosimetry Will Holmes-Smith described his experience with HexaCheck: “We 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. While 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 MIMI ensures image guidance accuracy by measuring the coincidence of isocentre prescribed by the lasers, treatment beam and image guidance systems. Five bone equivalent rods intersect at 90° 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 isocentre position. Fast and accurate alignment checks are established with mechanical stability of an image guidance system by verifying isocentre within 1mm. A 6.4mm sphere at the centre of the phantom
assists with virtual and physical graticule alignment checks.

OIS says the advantage of the HexaCheck MIMI phantom is that 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,” states the company.

Picture: The HexaCheck device allows secure integration with the MIMI phantom.

Published on page 17 of the April 2021 issue of RAD Magazine.

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