Extracting a disk shape from center of image

Good Day, I am working on extracting local features of a patterned image. I can find the radon transform of an image ([R,xp] = radon (img,theta);)

However, I would like to find the radon transform of a disk shape area at the middle of the image.

Is there any way to do this in Matlab?

Or is there a way to extract it from the image alone and then I can apply Radon?

Thank you in advance.