http://purl.org/tcl/home/man/tcl8.4/TkCmd/radiobutton.htm
Example:
Radio buttons are linked using a common variable, which will have the value of the selected button.
pack [radiobutton .one -value 1 -text "One" -variable onetwothree] pack [radiobutton .two -value 2 -text "Two" -variable onetwothree] pack [radiobutton .three -value 3 -text "Three" -variable onetwothree]
See the vertical command, which allows to place the text below the checkfield, on the checkbutton page.
Category Widget - Category Command - Tk syntax help - Arts and Crafts of Tcl-Tk Programming