Varian Medical Systems and Stanford University researchers netted a multi-million dollar, five-year research grant from the National Institutes of Health to improve CT imaging for patients with metal implants.

The $3.6 million grant will go to developing technology to correct for severe CT image distortion caused when metal objects, such as hip and dental implants, are present during scans.

CT scans are used to plan radiotherapy treatments for cancer, and cone-beam CT images are needed during treatment to position patients and gauge how well the tumor is responding to therapy.
But CT images, usually acquired with kilovoltage X-ray energies, are distorted by metal, according to Josh Star-Lack, senior scientist with Varians' Ginzton Technology Center and a principal investigator on the project. Doctors can reduce distortions by using high-energy, or megavoltage, X-rays to pass through the metal. However, this still presents problems.

"You need a lot of dose, and the quality of images is poor, particularly in soft tissues," Star-Lack said in prepared remarks.

For the project, Varian and Stanford researchers will create megavoltage X-ray detection hardware and image reconstruction software. The new technology will be tested in clinical trials run by the Stanford researchers.

"Our research grant will be used to develop tools to achieve the best of both worlds by combining kilovoltage cone-beam CT data with a limited amount of megavoltage data to create a composite image with less distortion and good soft tissue resolution," Star-Lack said.

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