I am trying to create a spherical ROI mask in the form of a volume file with 2.5 cm radius. I also have to specify the center of the ROI location. What is the best way to accomplish this?

I intend to use this to extract freesurfer cortical thickness values for a region-of-interest (ROI) defined in volume space as described in https://surfer.nmr.mgh.harvard.edu/fswiki/VolumeRoiCorticalThickness