For image-guided proton therapy, we investigated the feasibility of CBCT (cone-beam computed tomography) and
CBDT (cone-beam digital tomosynthesis) technologies in the gantry treatment room. A fully equipped x-ray projection
system, which was originally operated for patient alignment, in parallel to proton-beam direction was utilized for
acquiring CBCT/CBDT. The performance of the imaging detector was analyzed in terms of MTF (modulation-transfer
function), NPS (noise-power spectrum) and DQE (detective quantum efficiency). Tomographic imaging performances,
such as spatial resolving power, linearity of CT numbers, SNR (signal-to-noise ratio), and CNR (contrast-to-noise ratio),
were analyzed by using the AAPM (American Association of Physicists in Medicine) CT QC phantom. Geometric
alignment of CBCT/CBDT system was analyzed by using a calibration phantom, which consists of steal ball bearings.
The determined calibration parameters were applied to the image reconstruction procedures. The overall CBCT
performances of the system were demonstrated with reconstructed humanoid phantom images. In addition, we
implemented the CBDT with a selected number of projection views acquired for CBCT in limited angle ranges. From the
reconstructed phantom images, the CBCT system in the gantry treatment room will be very useful as a primary patient
alignment system for image-guided proton therapy. The CBDT may provide fast patient positioning with less motion
artifact and patient doses.