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Dose response characteristics of a novel CCD camera-based electronic portal imaging device comparison with OCTAVIUS
Akbar Anvari1, Seyed Mahmoud Reza Aghamiri, Seyed Rabie Mahdavi
1Department of Radiation Medicine Engineering, Shahid Beheshti University, Tehran, Iran.
Aim:
Dosimetric properties of a CCD camera-based Electronic Portal Imaging Device (EPID) for clinical dosimetric application have been evaluated. Characteristics obtained by EPID also compared with commercial 2D array of ion chambers.
Materials And Methods:
Portal images acquired in dosimetry mode then exported raw fluence or uncorrected images were investigated. Integration time of image acquisition mode has adjusted on 1 s per frame.
Results:
As saturation of camera of the EPID, dose response does not have linear behavior. The slight nonlinearity of the camera response can be corrected by a logarithmic expression. A fourth order polynomial regression model with coefficient of determination of 0.998 predicts a response to absolute dose values at less than 50 cGy. A field size dependent response of up to 7% (0.99-1.06) relative OCTAVIUS detector measurement was found. The EPID response can be fitted by a cubic regression for field size changes, yielded coefficient of determination of 0.999.
Conclusions:
These results indicate that the EPID is well suited for accurate dosimetric purposes, the major limitation currently being due to integration time and dead-time in frame acquisition.
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