You can choose from a couple of approaches in order to implement this scenario. You can handle the RadToggleButtons Checked() event to uncheck every other ToglleButton in the group. You can also use the RadToggleButton in an ItemTemplate for a ListBoxItem and bind the IsChecked property to the IsSelected property of the ListBoxItems.
You can also use the RadRadioButton instead of the RadToggleButton since it implements this functionality out-of-the-box.
I prepared a sample project illustrating all of these approaches. I hope it will help you choose the best approach towards your scenario.
the Telerik team
Browse the videos here>>
to help you get started with RadControls for WPF