How to use Cuda Compiler "nvcc" to comile Geant4 projects

I am really sorry for posting my problem here again for some data losing problem.
My problem is that i would need to change my Geant4 computing environment from CPU to GPU.
And i am here to ask for help for how to change the compiling environment suited for CUDA programming.
The first thing came to my mind is CUDA compile “nvcc”.
But i rally don’t know how to make it work for such a huge project of Geant4.
Do anyone have the same experience or have some good idea to share with me?
I would really appreciate it.