Erase some area of the custom QGraphicsItem

[NasserAll]

hi, I`m trying to clear(erase) a hole bounding rect or some part of this. how can I do this?
tanx

[NasserAll]

let me explain. I try to draw a cubic bezier and when i want to re-size this with control handlers the image below will apear. I try painter->eraseRect() function. but it dose not work....
!http://s14.postimage.org/br5hsabm9/Screenshot_at_2012_03_08_06_01_26.png(bezier curve drawing problem)!