Bai et al. recently proposed to acquire random fanbeam/cone-beam projections with a linear/planar detector from a circular scanning locus for controlled cardiac computed tomography (CT). After specifying a uniform acquisition geometry required by FBP (filtration-backprojection), we rebin the random fan-beam/cone-beam data via nearest-neighbor, quadrilateral and triangle-based linear interpolati...

background: during radiotherapy treatment, critical organs are shielded using lead and cerrobend blocks. the objective of this study is to compare the effects of lead and cerrobend shielding blocks on incident photon beam. methods: collimator scatter factors were measured for open square fields (3 x 3 cm to 40 x 40 cm) defined by collimator jaws and for fields blocked down to smaller asymmetric...

Using a recently developed time domain numerical approach we calculate the short-range geometric wakefields of 3D collimators and compare with analytical models. We find, in the diffractive regime, that the transverse mode kick factor can be approximated from the change in field energy between the beam pipe and the collimator if the collimator is long, or using a “field clipping” estimate if it...

The SLC final-focus system accommodates 29 fixed or adjustable collimators for machine protection and background reduction. By amplifying pulse-to-pulse orbit variations and by generating emittance growth, collimator wake fields may degrade the beam quality at the interaction point (IP). In the SLC final focus, collimator halfapertures are larger than the bunch length, so that the standard coll...

We propose a novel method to reduce the noise in fan-beam computed tomography (CT) imaging. First, the inverse Radon transform is induced for a family of differential expression of projection function. Second, the diffusion partial differential equation (PDE) is generalized from image space to projection space in parallel-beam geometry. Third, the diffusion PDE is further induced from parallel-...

Collimation of the multi-MW beams in present linear collider designs is a critical issue. Graphite as a possible collimator material exhibits good mechanical properties but a rather poor electrical conductivity. The resulting resistive wakefields can potentially deteriorate the beam quality. The knowledge of strength and scalings of such wakefields is essential for the design of the collimation...

We present a direct measurement of the short-range wakefield of a series of tapered collimators. The wakefields were measured by inserting a fixed aperture in the path of the electron beam at the 1.19 GeV point of the SLAC linac. As the vertical position of the collimator is varied, the vertical deflection of the beam is measured on 29 downstream beam position monitors. A series of apertures wi...

Helical tomotherapy has been developed at the University of Wisconsin, and 'Hi-Art II' clinical machines are now commercially manufactured. At the core of each machine lies a ring-gantry-mounted short linear accelerator which generates x-rays that are collimated into a fan beam of intensity-modulated radiation by a binary multileaf, the modulation being variable with gantry angle. Patients are ...