AbstractID: 9333 Title: Low dose-high contrast megavoltage cone beam CT
A high performance EPID system was developed for Low Dose-High Contrast Cone Beam Mega-voltage CT. The primary goal is to
use one detector such as an a-Si flat panel detector and one radiation source for MVCT and conventional therapy imaging. Three main
requirements are:
(i) increase the SNR significantly to acquire low dose MVCT, (ii) improve the contrast of the soft tissue, (iii) avoid saturation of the
a-Si sensors during radiation therapy.
A low noise cone beam acquisition mode is implemented to perform volume MVCT in the cone beam geometry to visualize 3D
anatomy during patient positioning. The image acquisition is synchronized with the linear accelerator to improve the SNR.
The other contributor to the SNR, contrast, and spatial resolution improvement is the removal of the flattening filter from the path of
the X-ray photons generated by the target during MVCT imaging (or patient positioning). This modification of the treatment head
does not affect the normal clinical operation of the machine. The collected empirical low energy scatter data is linked and corrected
(software corrections) for the acquired images to increase the image contrast.
Radiation as low as 0.026MU was used to form projection images. The reconstruction was made from 190 projections of the Head
phantom which were acquired over 190 degree (starting from 265° and ending at 95°) in 90s with the total exposure of 5MU. The
improvement in the soft tissue contrast and f50 obtained by removing the flattening filter (during MVCT or patient positioning) are
30% and 22%, respectively.
Sponsored by Siemens.