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Flat Panel Arrays Aid Radiotherapy, Diagnostic Imaging

Photonics Spectra
Mar 1998
Kathleen G. Tatterson

When administering radiation therapy to cancer patients, doctors must be able to monitor the amount of radiation going to the tumor as well as to the surrounding tissue. Physicians at the University of Michigan Medical Center use imagers incorporating flat panel amorphous silicon sensor arrays from dpiX, a Xerox New Enterprise Company, for accurate radiotherapy and diagnostic imaging in real time.

Cancer patients who are not candidates for surgery or chemotherapy undergo radiation therapy to kill their malignant lesions. Doctors direct very high energy x-ray beams at tumors from different directions. "It's hard to know whether the radiation has gotten all of the tumor from each direction," said Larry E. Antonuk, a physicist in the center's radiation oncology department.

Amorphous-silicon technology allows dpiX's flat panel image sensor arrays to produce clear, digital x-ray images in real time inexpensively.

Traditional film imaging of a tumor takes too long for the doctor to react to, and other electronic means yield poor-quality images. Also, because film is not digital, doctors cannot share information in real time. "All modalities in radiology are digital except film," said Jean-Pierre J. Georges of dpiX.

Truly lightweight

X-ray image intensifiers can be accurate but are very bulky and expensive. The average x-ray intensifier weighs around 300 pounds and can cost between $15,000 and $100,000, depending on the integration. For some applications, devices incorporating dpiX's flat panel arrays can weigh as little as 10 to 20 pounds.

Active-matrix flat panel imagers employ thin-film transistors to read out the charge acquired by each pixel in the array, which makes each pixel addressable. A phosphor screen converts x-rays into light that the photodiodes detect in a process known as indirect conversion.

Antonuk also sees advantages to using the flat panel imagers for diagnostic imaging. Traditional means of diagnostic imaging, fluoroscopy and radiography, are not digital and therefore cannot be shared electronically in real time. Use of active-matrix flat panel imagers can create digital information that not only can be shared, but is of very high image quality, eliminating image degradation defects and geometric distortions inherent to film. "The problems associated with film disappear with the flat panel imagers," he said.

Down the road

He envisions the technology to be even more useful in radiation imaging down the road. "Clinics will be able to use the technology as a tool to make cancer treatment more accurate, to maximize the tumor dose and minimize the dose to surrounding tissue in real time," Antonuk said.

DpiX acts as an OEM for companies that build imaging systems for medical and nondestructive testing applications. The company also has developed the FlashScan 20 image sensor, using a 20 3 25-cm, 127-µm- pixel array, calling it "a compilation of what makes sense on the market to meet the broadest possible requirements." It plans to release the FlashScan 30, based on a 30- to 40-cm array, by the end of March for clinical radiography applications.

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