Is it possible there are multiple once?
…well it kinda doesn’t matter. If you can overlap multiple once you will need an array and check each.
You need a variable to hold them. You create an “Event begin overlap” and cast that to your radiationsphere. If it’s successful you save it in your variable (you will have to remove it on “event end overlap”).
If your variable is valid you run the snippet you showed in your start post and input the new variable into the cast node.
That should do the trick 