Customizing OpenFileDialog

I am working on winforms application in C#. What I want to achieve is to get a file from user for which I am using the following code:

OpenFileDialog dlg = new OpenFileDialog();
if (dlg.ShowDialog() == DialogResult.OK)
{
    string sFileName = dlg.FileName;
    //my code goes here
}

Now, everything is working fine but I want to put 3 radio buttons in the same dialog box, meaning I would now get two things from this dialog box

string sFileName = dlg.FileName; //same as in case of traditional dialog box
//some thing like this which tells which radio button is selected:
dlg.rbTypes.Selected

How do I achieve this?