Cómo hacer que la casilla de verificación sea circular usando Flutter

shape: CircleBorder(), // circle checkbox
shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10.0)), // circle checkbox
shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(5.0)), // rounded corner checkbox
shape: RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(5.0))), // rounded corner checkbox 
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