How to access UserForm radio button Caption

Many thanks to Evgeny in tech support for this solution:

// In this example, a form named MyForm contains a radio button group
// named radioGroup.

// Display a modal form
var frm = UserForms.MyForm;
var modalResult = frm.ShowModal();

// Get the selected radio button
var idx = frm.radioGroup.ItemIndex;
var rb = frm.radioGroup.ChildControl(idx);

// Access properties on the radio button control
var selectedCaption = rb.Caption;

Note that code completion doesn't display any properties or methods for the radio button object.