projection of circle mask of image

Dear all, I'm trying to make a circular mask of the image (Modified Shepp-logan) by the following code :

I=imread(p.JPG);
while (p.JPG) is the image of Modified Shepped-logan in JPG format  
  imageSize = size(I);  
  ci = [128, 128, 118];  
  [xx,yy] = ndgrid((1:imageSize(1))-ci(1),(1:imageSize(2))-ci(2));  
  mask = uint8((xx.^2 + yy.^2)<ci(3)^2);  
  croppedImage = uint8(ones(size(I)));  
  croppedImage(:,:,1) = I(:,:,1).*mask;  
  croppedImage(:,:,2) = I(:,:,2).*mask;  
  croppedImage(:,:,3) = I(:,:,3).*mask;  
  imshow(croppedImage);

How do I make a projection of the circular mask using radon or fan beam projection??? When I wrote the code using radon, an error occurred.

[Image Analyst]

I fixed your formatting, but please read this for next time. By the way, since p.JPG must be a character string holding a filename, what does while (p.JPG) mean to you?