Remove Close(X) Button from WPF Window

Question

Can anyone tell me how to remove the close (X) button from a WPF window? I can disable it by following code but can not remove it:

    private const uint SC_CLOSE = 0xF060; 
    [DllImport("user32.dll")] 
    private static extern IntPtr GetSystemMenu(IntPtr hwnd, bool revert); 
    [DllImport("user32.dll")] 
    private static extern bool DeleteMenu(IntPtr hMenu, uint position, uint flags);

    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        WindowInteropHelper helper = new WindowInteropHelper(this); 

        IntPtr hwnd = GetSystemMenu(helper.Handle, false); 

        DeleteMenu(hwnd, SC_CLOSE, 0); 

    }