QGraphicsItem point selectable "Problem in Zoom"

Hi

My Scene have some many points, this points are a personal QGraphicsItem,
I tried this points can be movable and selectable, but when the points are very close is very hard select one, then zoom the scene and can view this points separated but the problem to select one points is the same, I think the problem is the boundrect, because this is more large than the distance of the points...

How can I solved this problem??
I used Qt 4.5.2 and attach the code of points