Use helper or library in Radius Tags

Hello,

I need to use some methods in Radius Tags and one of my Controllers.
I created a method after my tags definitions and access it from my tags,
it’s working.
I saw the tags are send to the Page model. So I can’t access to them
from my controller.
How could I create a common library which is accessible from anywhere
(including Radius Tags) ?

Thanks,
Vincent