How to find circle bBox?

Hello, 

following my last post, another question comes to me: how to get the bBox from the Place_Bound_Top of a circle?

I know I could do symbol->bBox but for certain reasons, this give me wrong coordinates (much larger than expected).
So I tried something else : I first get the Place_Bound_Top of a symbol and then I search its bbox. 
But for a circle, this return the center point and a point on the edge of the circle, wich is obviously not what I wanted.

Here is my code: ("composant" is a symbol)

foreach(c composant->children
 when(c->layer == "PACKAGE GEOMETRY/PLACE_BOUND_TOP" 
 foreach(item c->segments
 coordonnes_PBT = cons(car(item->startEnd) coordonnes_PBT) 
 ) 
 ) 
 ) 
when(coordonnes_PBT != nil then 
 bBox_PBT = axlGeoGetBBox(coordonnes_PBT)
)

I don't know where I'm wrong.
Can anyone help me please? 
Thank's