Register two 2D images (EPID and DRR)

Hi,

I would like to register two 2D images in 3D Slicer, one is an EPID image and the other is a computed DRR. Unfortunately, the EPID image does not contain any geometric information, so it is placed arbitrarily when loaded into 3D Slicer.

I tried using the Transform module, but applying the coordinates of the DRR’s position as transformation parameters does not align the EPID with the DRR plane. I also attempted registration with the General Registration (BRAINS) module, but it did not work because the images are 2D and lack a third dimension. Do you have any suggestions on how to correctly align or register 2D images in 3D Slicer?

Thanks in advance for your help!