How to use G4 to calculate the uncertainty of anisotropic functions

In our experiment, I intend to use G4 to obtain the radial dose function of the radioactive source, I first obtained the absorbed dose at different distances and afterwards calculated the radial dose function according to the TG-US formula, but I see that the uncertainty of this function is calculated in many papers, I would like to ask you all how I should calculate this uncertainty. Thank you for your replies.