Render Material to texture(Need Texture Buffer?)

Assume we have a material using an algorythm to create an image.

This created image / texture needs to be stored at runtime somewhere.
In the next rendering step, the material reads the previously stored old texture of himself, adds the old results to the
algorythm and creates a new image with them.

How can that be implemented in UE4? In need some way to store the render result of the material at runtime.