How to draw circle around the user-clicked curve point

Hi, how can I draw circle around the user clicked point on the curve? I can already draw the curve to the QwtPlot and change the curve realtime when the user clicks and moves the curve. What I want to do is, to draw a circle around the user-clicked point on the curve, to indicate that it is a previously clicked control point..
Any idea is welcome..

You could insert a marker with an ellipse as symbol - with a pen but no brush.

Uwe

Ok thank you very much.