When the Anisotropy F(φ) item is checked in the Dose calc. options menu, or the Isotropy button in the Prescription window is "on" (ie down), the source anisotropy function F(r,φ) is included in the dose calculation. The anisotropy function F(r,φ) is a two-dimensional function which gives the angular variation of dose rate about the source at each distance due to self-filtration, oblique filtration of primary photons through the encapsulating material, and scattering of photons in the medium. F(r,φ) is calculated by removing a geometry factor G(r,φ) from measured data. Plaque Simulator expects anisotropy data for at least r = 0.5, 1.0 and 2.0 cm.

To expedite the dose calculation, Plaque Simulator uses a 91 element extended F[φ] lookup table covering the range 0..90 degrees at increments of 1 degree. The lookup table is interpolated from up to 20 data pairs. The default data in Plaque Simulator is from the r=1 cm data in Tables VIII to XI in AAPM TG43 (Medical Physics, Vol. 22, 1995, pages 216-217). Definition points must be entered for 0 and 90 degrees, the remaining 18 points may be distributed in any way you like.

The distance at which the data was measured (r cm) and the source length (L cm) may optionally be entered for completeness although the r and L parameters are not currently used by Plaque Simulator.

For the BEBIG Ru106-Rh106 plaques the anisotropy kernel data accounts for beta attenuation and spectral hardening in the concave direction from a point source.