Hi Lozang,
The abnormal cells seen in DCIS are actually cancer cells but they have not yet spread out from the milk ducts - if they had that would be invasive ductal carcinoma (see: canceraustralia.gov.au/affected-cancer/cancer-types/breast-cancer/about-breast-cancer/types-breast-cancer/what-ductal-carcinoma-situ-dcis), so although it is confusing, as DCIS is often called a pre-cancer or non-cancer, it actually is simply referring to the fact that the cells have not yet become invasive and therefore life-threatening.
The big problem at the moment is that no-one is yet able to predict who will develop invasive cancer after a diagnosis of DCIS, so the standard treatment is surgery, and possibly radiation and hormone therapies (if oestrogen positive) depending on your personal risk profile.
It is important that you speak to the radiation oncologist about your risk of recurrence and to discuss the pros and cons of this treatment with them so that you have a good basis to make the decision that is right for you based on your circumstances.
It is all a bit of a gamble, but it can be reassuring to know that you have done everything possible not to be travelling down this path again. My mum had a similar diagnosis to you and decided to have radiation (although it meant leaving home for 6 weeks) and had hormone therapy for 5 yrs and I'm happy to say she has been cancer-free for the past 15yrs.
Best of luck with your decision and hope all goes well for you. Jane xx