Digitally Reconstructed Radiograph Using Models Instead of Volumes

Hi Guys! Although this is an older topic I thought I give it a try since I have a similiar question:

The uploaded picture is an orthographic projection of a STL Design I did, which shall mimic a female breast parenchym in Mammography. I created the projection using an orthographic projection script in python.
So much for the introduction, now here is my problem: I want to use 3D slicer to create a more advanced orthographic projection, like a DRR. I have voxelized the STL file and want every voxel that is filled, to have a certain attenuation A, and all the space inbetween (so all empty voxels) to have a certain attenuation B. Thanks in advance for your help!