The radial dose function g(r) is based on measurements in homogeneous medium (e.g. water) with full scatter geometry. When sources are placed in a plaque with a high-Z backing material such as gold, lead or silver, these conditions no longer apply. Scatter originating behind the plaque is reduced and L-shell flouresence from the gold is added. The scatter modifier function B(r) attempts to compensate for deviation from a homogeneous full scatter geometry.
Important: Scatter and flourescence correction are already included in the carrier correction factor T(r,u) for COMS plaques which use a silicone carrier because the flourescence is absorbed in the silicone. The scatter modifier B(r) should be disabled for a COMS plaque that uses a silicone carrier, but enabled for a COMS plaque that uses a gold insert instead of the silicone.
The B(r) function applies specifically to plaques that use I or Pd seeds, not Ir. For the BEBIG Ru106-Rh106 plaques this parameter is used instead to store additional anisotropy kernel data for the convex direction from a point source.
To expedite the dose calculation, Plaque Simulator uses a 2001 element extended B(r) lookup table covering the range 0..40 mm at increments of 0.02 mm. The B(r) lookup tables are interpolated from a table of 20 data pairs describing the function in the range 0..40 mm. The data that has been installed in Plaque Simulator's resources is from our published measurements. For r > 40 mm, B(r) = coefficient a0.