River Play with a Set?

[TiltedFox]

Sorry about formatting, not at home [img]/images/graemlins/frown.gif[/img]

Middle position with 22. Two caller before me, so I go 4x BB. Two callers behind, original callers fold.

Flop 524 rainbow.
Half pot sized bet, both insta call.

Turn 3
Half pot sized bet, both insta call.

River a blank.
Hero?

My thinking here is that any Ax now has me beat. If I bet and get reraised I'm probably going to have to fold, even if they are bluffing. If I check and they put out a mid sized bet it would probably be easier to call. Any thoughts?