  Adaptive Radiation Therapy (ART) was developed based on Image-guided
Radiation Therapy (IGRT) and it is the trend of photon radiation therapy. To
get a better use of Cone Beam CT (CBCT) images for ART, the CBCT system model
was established based on Monte Carlo program and validated against the
measurement. The BEAMnrc program was adopted to the KV x-ray tube. Both
IOURCE-13 and ISOURCE-24 were chosen to simulate the path of beam particles.
The measured Percentage Depth Dose (PDD) and lateral dose profiles under 1cm
water were compared with the dose calculated by DOSXYZnrc program. The
calculated PDD was better than 1% within the depth of 10cm. More than 85%
points of calculated lateral dose profiles was within 2%. The correct CBCT
system model helps to improve CBCT image quality for dose verification in ART
and assess the CBCT image concomitant dose risk.
