Mine was also on the muscle. So I to ended up doing radiation. I'm 1/2 way through and the skin is just starting to tighten. My expander is also starting to look a little deformed They told me that the radiation would destroy the expanders (they were glad I didn't have my permanent in because it would have destroyed it). I think it must harden the wall of the implant. Hopefully they used the temporary implants in you knowing it was on the muscle and you would need radiation. GOOD luck. My thoughts are with you.