Debris Disk Radiative Transfer Simulator Manual  Upload: Density Distribution. General Remarks. 

If n0(r,theta,phi) is the arbitrary (optically thin) density distribution, the radial density distribution n(r) required for the simulation of the spectral energy distribution can be derived as follows (simply averaging): The quantity r is the radial distance
to the illuminating star.
When providing the set of (r, n(r)) pairs, consider the following:
See here , if you plan to upload a density distribution resulting from nparticle simulations. 