The ray tracing inspector window is used to verify Plaque Simulator's dosimetry ray tracing algorithms. The table lists the ocular regions for which Plaque Simulator keeps track of linear path length, density relative to that of water and effective Z encountered by a vector between selected endpoints. In this example the vector originates at the center of source #12 in the plaque and is directed towards apex of the cornea. Ray tracing enables Plaque Simulator to estimate the dosimetric effects of inhomogeneities such as lens, sclera and substitution of vitreous humor with Si oil whose densities and effective atomic numbers differ, perhaps significantly, from those of water. Radiation attenuation at I-125 and Pd-103 energies results primarily from photoelectric interactions which are significantly affected by these atomic properties compared to greater energies for which attenuation largely results from Compton scattering interactions.

The purple 10.0 Gy isodose lines in the examples below illustrate the additional attenuation in the lens due to its greater density and effective atomic number compared those values for water. It is more difficult to observe inhomogeneity difference for the other ocular materials because the differnces compared to water are small and the path lengths crossing those regions tend to be quite short.

Note: in the provided example, ray tracing considers the 1.325 mm of silicone Silastic that the ray traverses within the COMS plaque's carrier to be water equivalent because attenuation within that segment of the path has already been handled by a carrier correction factor that has been used by Plaque Simulator going back to the 1990s versions and which already accounts for the differences between silicone Silastic vs water. The curent ray tracing is basically an extension of that earier ray tracing that can now be applied to the entire eye without noticably slowing the 3D calculations because modern computers are now so much faster and support far more RAM to maintain the voxel model than they were in 1990. The default dimensions of a voxel are 0.4 x 0.4 x 0.4 mm but you may optionally decrease that to 0.1 x 0.1 x 0.1 mm voxels via a preferences setting if you have sufficient RAM and need to support the 0.1 mm resolution model. Each voxel uses one byte to encode its tissue type. The ray sampling increment defaults to 0.1 mm which can also be customized via a model preferences setting.