I am currently doing radiation therapy for breast cancer. what kind of deodorant can i use?

Ask your rad doc: Ask your radiation oncologist or the therapist. They get this question a lot. It depends on where the radiation fields are located, your reaction to the radiation, and the doc's personal preferences. You want to avoid irritation.

None: The effects of radiation alter the skin. The skin can become irritated itself by the radiation. Today there is much less likelihood of "burns". But, still washing yourself with a mild antibacterial soap and gently drying the area is the most you can do; unless the radiation oncologist tells you a different method. The skin is sensitive.