Getting isocenter coordinates with respect to another image

Dec 9, 2015 at 11:52 PM
I'm working on mapping isocenter of a CT image to another CBCT image. I got isocenter of the plan and i got it displayed on a CT image. The isocenter gets marked correctly for the CT image. Now i can't use same isocenter coordinates for CBCT images because there can be some sort of transformation or translation between CT and CBCT images.
How do I get transformation and translation matrix for CBCT image so that it can be aligned with CT image.
Or can i just get the factor by which my plan isocenter works for CBCT image (treatment isocenter)