How to made Circle world bound? Or How to made custom Circle bound?

Phaser 2 / CE
1

Hi. I am making circle collide game.

The scenarios are as follows:

  1. exist two circles. (one is big, another is small)
  2. small circle inside big circle (big circle is a boundary)

I tried to make circle world boundary.
But world bounds only supports rectangle.

how to make this? Please let me know.