This is Dr. David
I am a radiation oncology doctor.
surgery and radiation can cause scar tissue.
best thing is moisturizing the skin and massaging the area.
scar tissue forms in the first 3-6 months after radiation completes
your doctors should have talked to you about stretching and massage therapy of your breast to minimize scar tissue after radiation therapy.
you can try Mederma anti scar creams as well.
let me know if you have questions.