INPUT/OUTPUT CHARACTERISTICS OF A MATRIX ION-CHAMBER ELECTRONIC PORTAL IMAGING DEVICE

被引:45
作者
YIN, FF
SCHELL, MC
RUBIN, P
机构
[1] Oncologic Imaging Research Laboratory, Department of Radiation Oncology, University of Rochester Cancer Center, Rochester, New York, 14642, 601 Elmwood Avenue
关键词
PORTAL IMAGE; ELECTRONIC PORTAL IMAGING; CHARACTERISTIC CURVE;
D O I
10.1118/1.597190
中图分类号
R8 [特种医学]; R445 [影像诊断学];
学科分类号
1002 ; 100207 ; 1009 ;
摘要
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 5x5 cm(2). The output pixel value of the EPID is represented by the average pixel value of a region of interest of 9x9 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 same 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.
引用
收藏
页码:1447 / 1454
页数:8
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