How would you counsel a young female patient who refuses to use contraception during radiotherapy?

Would your counseling change if she reported a history of unplanned pregnancy? Is there any wording or waiver you might be able to use warning her of the risks of RT to an unplanned pregnancy if she continues to refuse to use contraception? Or perhaps would you decline to treat a patient who refuses to use birth control while on treatment? What if the patient is not a candidate for birth control pills due to a diagnosis of breast cancer, but also does not want to use a copper IUD?