The placement looks good on that page dentistolgy, though as nomis5 says, it's absolutely flush against your text, and I'd give it a little breathing room.
As to the CTR and CPC, I'm afraid I've no idea what might be causing those fluctations! Hope you get to the root of the problem. The ads I get (interest based, though poorly chosen on my interests!) are 75% off hotels worldwide, improve your brain and euro millions. Perhaps you'd be better off having some bigger text only - they're usually far more relevant to site content then picture based ones.