"This is a marriage of two great technologies," Lionel Bouchet, Mevion's vice-president for technical and clinical partnerships, told medicalphysicsweb. "The ImagingRing, which is already in use at the MedAustron particle therapy centre, integrated within Mevion's Verity image-guided patient positioning system."

CBCT provides an important function in the treatment room, enabling the precise patient positioning required for pencil-beam proton therapy. And it does this rapidly – imaging in just two minutes, compared with 15 minutes for an in-room CT scan. "The demand on imaging is high in proton therapy, you have to have tools available to reduce uncertainty and increase treatment robustness," explained Bouchet. "The value of CBCT is in the workflow. It's not as good as in-room CT for dose calculations, but research is being done to develop techniques to overcome these limitations."

In a press statement, medPhoton's founder and CEO Heinz Deutschmann said: "The agreement with Mevion provides us the opportunity to integrate the industry's most compact proton therapy system, the MEVION S250 Series, with our slim, multi-purpose in-room CBCT system, providing large field-of-view, cutting-edge acquisition speed, spatial resolution, and outstanding low-contrast visibility at very low doses. We believe the products will complement each other and enable clinicians to truly optimize the proton treatments they can provide their patients."

Flexible and precise

According to Bouchet, the ImagingRing offers a range of advantages over other CBCT systems. It is integrated on a precision rail mounted on the wall, eliminating sagging problems that may occur with couch- or gantry-mounted imaging systems. The device is moved into position and locked onto the gantry for imaging and patient positioning, and can be moved out of the way during treatment.

ImagingRing incorporates an X-ray source and a flat-panel detector that can precisely rotate independently of each other. This design expands the range of potential applications and enables 2D and 3D extended field-of-view imaging. A mechanically stable closed ring allows the system to offer high image resolution, while a unique collimation system reduces patient dose. For example, ImagingRing can perform pelvic imaging using just 8 mGy. "This is a 68% reduction in dose compared with other OBI CBCT systems," said Bouchet.

While ImagingRing is targeted for patient positioning, in theory, it could also be used for imaging during treatment delivery. The independent movement of the tubes and panels should enable clearance from the proton nozzle. "There are no technology limitations, but this has not been tested yet," Bouchet noted.

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