From a Radiation Therapist point of view, it is harder to achieve the optimal plan on reconstructed breasts depending on how much of the chest wall is left and how the reconstruction has been done. When I was faced with the possibility of a mastectomy I knew I wouldn't get an immediate recon for that reason and my rad onc and plastic surgeon agreed.
But please be assured that the radiation therapists do everything possible to ensure the best possible plan is achieved if you do decide to go that way.
Best wishes x
