Megavoltage imaging with a large-area, flat-panel, amorphous silicon imager

Larry E. Antonuk, John Yorkston, Weidong Huang, Howard Sandler, Jeffrey H. Siewerdsen, Youcef El-Mohri

Research output: Contribution to journalArticlepeer-review

50 Scopus citations


Purpose: The creation of the first large-area, amorphous silicon megavoltage imager is reported. The imager is an engineering prototype built to serve as a stepping stone toward the creation of a future clinical prototype. The engineering prototype is described and various images demonstrating its properties are shown including the first reported patient image acquired with such an amorphous silicon imaging device. Specific limitations in the engineering prototype are reviewed and potential advantages of future, more optimized imagers of this type are presented. Methods and Materials: The imager is based on a two-dimensional, pixelated array containing amorphous silicon field-effect transistors and photodiode sensors which are deposited on a thin glass substrate. The array has a 512 x 560-pixel format and a pixel pitch of 450μm giving an imaging area of ~23 x 25 cm2. The array is used in conjunction with an overlying metal plate/phosphor screen converter as well as an electronic acquisition system. Images were acquired fluoroscopically using a megavoltage treatment machine. Results: Array and digitized film images of a variety of anthropomorphic phantoms and of a human subject are presented and compared. The information content of the array images generally appears to be at least as great as that of the digitized film images. Conclusion: Despite a variety of severe limitations in the engineering prototype, including many array defects, a relatively slow and noisy acquisition system, and the lack of a means to generate images in a radiographic manner, the prototype nevertheless generated clinically useful information. The general properties of these amorphous silicon arrays, along with the quality of the images provided by the engineering prototype, strongly suggest that such arrays could eventually form the basis of a new imaging technology for radiotherapy localization and verification. The development of a clinically useful prototype offering high- quality images, ultimately with an ~52 x 52-cm2 detection surface, is anticipated.

Original languageEnglish (US)
Pages (from-to)661-672
Number of pages12
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number3
StatePublished - Oct 1 1996
Externally publishedYes


  • Amorphous silicon array
  • Digital imaging
  • Flat-panel imager
  • Megavoltage imaging

ASJC Scopus subject areas

  • Radiation
  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Cancer Research


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