Rubber Band Straightening Transform

I have a mammogram image with the mass detected as ROI. Now I am interested in the boundary of the mass, so I extract out the boundary of the mass using circular cropping and put all other pixels in the image to 0. So basically I have an image like a ring. Now I want to Rubber Band Straightening Transform it to convert it to cartesin plane. Any help in this regard would be appretiated.

[KALYAN ACHARJYA]

I extract out the boundary of the mass using circular cropping and put all other pixels in the image to 0.

Can you share a sample image?