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

To expedite the dose calculation, Plaque Simulator creates up to 16 F[r] lookup tables which consist of 91 F[θ] elements covering the range 0..90 degrees in increments of 1 degree. The tables are linearly interpolated from up to 20 θ,F(θ) data pairs for each r. The default data in Plaque Simulator is from the r=1 cm data in Tables VIII to XI in AAPM TG43 (Medical Physics, V22, 1995). Definition points must be entered for 0 and 90 degrees, the remaining 18 points may be distributed in any way you like.

The source length (L cm) may optionally be entered for completeness although the L parameter is not currently used by Plaque Simulator.

Note: 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 rather than seed anisotropy.

When the **Anisotropy F(r,θ)** item is checked in the Dose Calc. Options menu, or the **Isotropy** button in the Prescription window is showing the anisotropic icon, the anisotropy modifier F(r,θ) is included in the dose calculation.