Optimal X-ray imaging geometry for flat-panel cone-beam computed tomography [prostate radiotherapy application]

A theoretical method for identifying optimal X-ray imaging geometry is presented and applied to cone-beam CT (CBCT) using a flat-panel imager (FPI). The method includes the effects of X-ray source distribution, imaging task, X-ray scatter, and detective quantum efficiency (DQE) on the ICRU-recommended figure of merit for image quality-detectability index. Cascaded systems analysis for FPIs is extended to incorporate the effects of X-ray scatter directly into the DQE. For the FPI-CBCT prototype being implemented for image-guided radiotherapy of the prostate, optimal magnification is /spl sim/1.4-1.6, depending primarily on the magnitude of the X-ray scatter fraction.