Calculate mean distance from a point to curved line


I have a highly deformed elongated bubble, and I need to calculate the mean radius along with a bubble.
For this reason:

  1. I extract a surface,
  2. take a slice along the bubble (then I have closed curves, the slice can be multiply-connected due to concavities inward)
  3. calculate the mean radius of the slice. Here I don’t know how to do it, Any ideas?
    Thank you in advance!