Two Saline Fillable Implants on old & new mastectomies

When I had my 2nd mastectomy in August I had double reconstruction with Mentor fillable implants that stretch your skin. The 2 yr. old mastectomy just never gets as big as the new one. The plastic surgeon said it was because the muscle was weakened due to radiation. Anyone else past this stage and have the permanent implants in yet? Will I always have one breast bigger than the other? A little disappointing, but I am happy to have breasts at all.