How to add n RT Dose volume in 3D Slicer

Slicer version: 4.11
Hi 3d slicer experts and all
I have 4 rt dose and I want to calculate the sum of them. How can I do this?
Thanks a lot

Using this module
https://www.slicer.org/wiki/Documentation/Nightly/Modules/DoseAccumulation

Here is the description of all the RT-related features
https://www.slicer.org/wiki/Documentation/Nightly/Extensions/SlicerRT