You can install extensions using Extensions Manager.
There are several methods, they have all pros and cons, so you can choose the one that best fits your needs:
- Using volume rendering module: magnitudes faster than any other methods, projection is set up by the 3D view’s camera, you can control properties of the X-ray, materials, and processing in the imaging system using a transfer function
- SlicerRT: new DRR module in SlicerRT, projection parameters are set up using beams, see above for details
- Thick slab reformatting using “mean” slab mode: projection parameters uses slice position and normal, can only compute parallel projection, see topic and script for details
- SlicerDRR generator: I don’t know much about this one, you need to contact the author if you have any questions