EventHandler[InputRange[0,1,0.1, "Label"->"Radius"], Function[value, radius = value]]
% // EventFire; (* just to initialize `radius` *)

Graphics[{LightBlue, Disk[], Pink, Disk[{0,0}, radius // Offload]}]

(*VB[*)(EventObject[<|"Id" -> "26972dcc-9eb4-435d-8f65-c1009adc90f9", "Initial" -> 0.5, "View" -> "8783fd1e-7623-4ba2-9bb8-3f27d772f295"|>])(*,*)(*"1:eJxTTMoPSmNkYGAoZgESHvk5KRCeEJBwK8rPK3HNS3GtSE0uLUlMykkNVgEKW5hbGKelGKbqmpsZGeuaJCUa6VomJVnoGqcZmaeYmxulGVmaAgB/+BVZ"*)(*]VB*)

(*VB[*)(FrontEndRef["3e245324-9210-43e7-b4d4-725026875b8f"])(*,*)(*"1:eJxTTMoPSmNkYGAoZgESHvk5KRCeEJBwK8rPK3HNS3GtSE0uLUlMykkNVgEKG6camZgaG5noWhoZGuiaGKea6yaZpJjomhuZGhiZWZibJlmkAQBruxSG"*)(*]VB*)