How to Calculate BNCT Dose Using Geant4?

I would like to know how to calculate the dose of BNCT using Geant4, hope to get your help

Hello Geant4 experts
“I want to create a source of thermal neutrons for BNCT. How can I do this?”
"Can you provide an appropriate Geant4 example or guidance for achieving this goal?"Thank you for help me