Segmenting brain images (Dicom format) using region-growing algorithm

I have a list of images in a folder where num denotes the index of image and I used num to run the iterations in a "for loop". The code is supposed to segment brain part from the brain CT images. Here is the link for region growing algorithm.

How do I increase the performance of my region-growing algorithm?

% CORD_XY(1),CORD_XY(2) is the seed point
% LEN Denotes the number of images in a folder    
% num is used to iterate in "for loop"
% "img" here is single image from the folder in DICOM format

for num= 1:LEN 
    img = dicomread(files(num,1).name);
    [row, col] = size(img);
    th = 20;
    diff = 10;

    J = regiongrowing(img, CORD_XY(1), CORD_XY(2), th);
    value1 = sum(sum(J > 0));

    if num > 10)
        th = 55;
    elseif num <= 10
        while diff < 0.2 * value1 && diff ~= 0 && th < 60
            value1 = sum(sum(J > 0));
            th = th + 10;
            J = regiongrowing(double(img), CORD_XY(1), CORD_XY(2), th);
            value2 = sum(sum(J > 0));
            diff = value2 - value1; 
        end
    end
end  

J = regiongrowing(img, CORD_XY(1), CORD_XY(2), th-10);