Filling drawn circles

I'm building a game at the moment, which sees the player drawing circles, which will then erase anything within those circles.

Is there any convenient way of doing this without using extensions. I've tried one approach, but it isn't so accurate.

My method involves checking for an overlap in lines (lines connect points spread as the mouse key is down) and if the user lets go and there is an overlap, long bars come in from each edge and stop when they reach one of the lines/points. This creates a rectangular shape which I can check position in comparison to, but it's really not that accurate (rectangle, rather than the circular shapes that can be drawn).

Is there any other ways?

I also apologise for making this thread again. I asked a while back but got no response.

Quote from ChrisBurrows

That was helpful. How exactly does the user draw the circles? Dragging a circle with the mouse? Or drawing it paint style?

There's ten or so points, which have lines scaled and rotated between them to connect them all. While the user is holding down the mouse key, every few milliseconds, it places one of these down and once the user lets go, they all move back to where they were.

But the problem is that the player can draw a really wide circle and it will act rectangular, so objects which are clearly outside the circle will be included.