Figure 1.

(a) A point source and an effective beam width were used in the simulations to account for the dose delivered by both the umbra and the penumbra regions of the beam. (b) The fan beam was chosen to be just broad enough to cover the imaging object. A pseudoimpact detector was added below the bowtie filter at the level of the tungsten cam collimators to register the information of each incident particle in a phase-space file for use in the subsequent simulations of axial and helical scans.