How to shade the intersection area between two overlay image?

I have two overlay image that intersect at two points,my aim is to calculate the area between this two curve.I don't know how to shade the area that is between two curve.this is my program:

RGB=imread('DETECTOR1.PNG');

A=imread('DETECTOR2.PNG');

F=imfuse(RGB,A,'blend','Scaling','Joint');

imwrite(RGB,'Detectors.PNG');

imtool(F);