Change of tumor location during registration with different templates

Dear ITK forum Members,

All our registrations are performed using Simple ITK.
T1 weighted image is registered with SRI24 atlas (240,240,155) as a template (1st image) and with MNI152 (197,233,189) atlas (2nd image). 2nd image is re-registered with SRI24 again (3rd image).

After registration, we observed that the tumor location is changing in SRI (1st image) and MNI (2nd image) registration for the same patient T1-weighted image. Could you please guide us why the tumor location is changing in SRI and MNI registered images?

In all these examples voxel volume is fixed that is 1 mm^3. However, non-zero voxel volumes are different for different template references for the same patient T1-weighted image as shown below.

Non-zero brain volume of SRI registered T1 image (1st Image): 1512233
Non-zero brain volume of MNI registered T1 image (2nd Image): 793562
Non-zero brain volume of MNI to SRI registered T1 image (3rd Image): 1710923

The main concern is that why the tumor location is changing with different reference template? Why there is a change in volume between 1st and 3rd image?

Your help will be highly appreciated.

Thank you so much.

Best regards,
Sunita

Dear Ziv,

You have expertise in this area. I am sure you have a solution for this.
Could you please guide.

Thank you so much.
Sunita