Photoshop to vector
Crafted Volume Tutorial in Photoshop
by - Tremorwave

I have started with a render with the standard colorisation below 

Set the brush as above and brush across the area required for general volume lighting
similar to that shown below.

Apply Filter --> Blur --> Radial Blur Zoom 100%. The result should be similiar to below

using the above eraser settings. Lightly brush over the lighting like the image below

Apply Filter --> Blur --> Gaussian Blur radius 2.5

Using the above settings for the lasso tool while holding shift select from parts of the render as shown below.
Now simply delete these unwanted areas from the volume light area.
Here is an example of it in use.
PS: Tutorial written with the permission of the Author!