Dose deposited in the DICOM example

Hello dear experts, I have some questions regarding the DICOM example of GEANT4.
I import the DICOM file for a phantom and i need to get the deposited dose in specific organ. The DICOM example deals with voxels.
So how can I irradiate the entire target organ, given that it is made up of several CT slices?
Similarly, i’m interested only in accumulated dose in specific organ how can I measure the dose deposited in the whole organ, given that it is also made up of several voxels spread over several CT slices?

If you have any suggestion I would be great full.
Thank you for your help!

The ROI called as region of interest, is a post processing analysis where you need to write your own code supporting 3dimensional representation of dose in secondary softwares such as AMIDE, etc.
Overlay CT images and dose deposition data of geant4, and create a ROI to know the volumetric dose in desired organ.

This is completely external feature of Geant4 though the data is of Geant4.

VRS