Dosimetric Characteristics of the Cine Acquisition Mode of An ASi EPID

O Bawazeer, S Sarasanandarajah, Sisira Herath, T Kron, Pradip Deb

Research output: Contribution to journalArticleOtherpeer-review


To investigate the dosimetric characteristics of Varian aSi500
electronic portal imaging device (EPID) operated in cine mode particularly considering
linearity with delivered dose, dose rate, field size, phantom thickness, MLC speed and common IMRT fields.
The EPID that attached to a Varian Clinac 21iX linear accelerator, was irradiated with 6 and 18 MV using 600 MU/min. Image acquisition is controlled by
the IAS3 software, Trigger delay was 6 ms, BeamOnDelay and FrameStartDelay were zero. Different frame rates were utilized. Cine mode response
was calculated using MATLAB as summation of mean pixel values in a region of interest of the acquired images. The performance of cine mode was
compared to integrated mode and dose measurements in water using CC13 ionization chamber.
Figure1 illustrates that cine mode has nonlinear response for small MU, when delivering 10 MU was about 0.5 and 0.64 for 6 and 18 MV respectively.
This is because the missing acquired images that were calculated around four images missing in each delivery. With the increase MU the response
became linear and comparable with integrated mode and ionization chamber within 2%. Figure 2 shows that cine mode has comparable response with
integrated mode and ionization chamber within 2% with changing dose rate for 10 MU delivered. This indicates that the dose rate change has no effect
on nonlinearity of cine mode response. Except nonlinearity, cine mode is well matched to integrated mode response within 2% for field size, phantom
thickness, MLC speed dependences.
Cine mode has similar dosimetric characteristics to integrated mode with open and IMRT fields, and the main limitation with cine mode is missing
images. Therefore, the calibration of EPID images with this mode should be run with large MU, and when IMRT verification field has low MU, the
correction for missing images are required.
Original languageEnglish
Article numberSU-F-T-263
Pages (from-to)3523
Number of pages1
JournalMedical Physics
Issue number6
Publication statusPublished - 2016
Externally publishedYes
EventAnnual Meeting & Exhibition of the American Assocation of Physicists in Medicine - Washington, DC, United States of America
Duration: 31 Jul 20164 Aug 2016
Conference number: 58th

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