Input/output characteristics of a matrix ion-chamber electronic portal imaging device.

Journal Article (Journal Article)

The input/output characteristics of a matrix liquid ion-chamber electronic portal imaging device (EPID) are investigated to elucidate the imaging properties of EPIDs. The radiation input to the detector, represented by dose rate, and the pixel value output from the device are related by a characteristic curve. Various incident radiation intensities are obtained by changing the source-to-detector distance (SDD). For each incident radiation intensity, an electronic portal image is obtained using a field size of 5 x 5 cm2. The output pixel value of the EPID is represented by the average pixel value of a region of interest of 9 x 9 pixels centered at a selected point. The effects of various accelerator settings, such as the repetition-rate setting and photon energy, gantry angle, field size, SDD, and acquisition mode of the EPID on characteristic curves are investigated at the central axis. The off-axis response of the detector is also examined. The derivative of the pixel value with respect to the input dose rate is used to analyze the detector contrast. Results indicate that the output pixel value is not a linear function of the incident radiation intensity. The detector contrast is comparable between photon energies of 10 and 6 MV and increases at low dose rates. The response of the imaging device varies substantially with acquisition mode, but is less sensitive to the SDD used for calibration. Characteristic curves are consistent for different gantry angles at the central axis and with the off-axis locations when the gantry angle is used for imaging and calibration, but vary with off-axis locations when the gantry angle is not at the calibration direction. Characteristic curves are also found to vary with different field sizes, but are similar in shape.

Full Text

Duke Authors

Cited Authors

  • Yin, FF; Schell, MC; Rubin, P

Published Date

  • September 1, 1994

Published In

Volume / Issue

  • 21 / 9

Start / End Page

  • 1447 - 1454

PubMed ID

  • 7838056

International Standard Serial Number (ISSN)

  • 0094-2405

Digital Object Identifier (DOI)

  • 10.1118/1.597190


  • eng

Conference Location

  • United States