Bind Xaml Radio button to boolean

Bind Xaml Radio button to boolean

I saw many posts on how to bind a boolean value to a radio button. But my
scenario is that I need to bind it to a radio button and read the
selection from the user.
That is no option should be selected intially.
If I bind it to a boolean, since boolean cant be null it shows the default
value selected in radio button.
If I use nullable boolean, I still defaults to false when trying to use
the converter.
I cant use oneway mode in xaml as I need to check if the radio button
selection was made which I do using the bounded variable.
Ant pointers on how to achieve this?