Radius instead of diameter in voxel range calculations?

[lk251]

Forgive me if I've misunderstood, but shouldn't the radius be added and subtracted in the calculations below, instead of the diameter, if we're trying to determine the voxel range of the nodule?
Also, am I wrong in assuming that the 5 voxels added to each end of the range is some sort of padding?
Thank you.

    v_center = (center-origin)/spacing
    v_diam = int(diam/spacing[0]+5) 
    v_xmin = np.max([0,int(v_center[0]-v_diam)-5])
    v_xmax = np.min([width-1,int(v_center[0]+v_diam)+5])
    v_ymin = np.max([0,int(v_center[1]-v_diam)-5]) 
    v_ymax = np.min([height-1,int(v_center[1]+v_diam)+5])

[hllcy]

I have the same doubt. And is the "diam/spacing[0]" an approximation?