Hi Lozang,
I was in your position about 10-11 months ago and I declined radiation. Like you I was DCIS, high grade, also ER+ve, lumpectomy with clear nodes, no microinvasion though. I made the decision about 10 mins into the appoint with the radiation oncologist that I wouldn't be doing it. I went to my normal oncologist and talked it through with her as well. Both she and my breast surgeon wanted a mastectomy if I declined the radiation and they were able to provide me with enough evidence that it was a good thing, I trust my BS implicitly as she has been down this path herself. I also chose to have hormone therapy as I saw how many additional quality years it gave my mum, initially Tamoxifen but after I had a total hysterectomy + BSO in Sept and became post menopausal even though I am only 42, I changed to Arimidex. I did all that in conjunction with a naturopath, who is also an oncology nurse, so I am able to really discuss my treatment options and symptom management with her and know that she isn't going to compromise my mainstream treatment.
There were 2 main reasons I declined the radiation. 1st, the cancer was directly over my heart and at 41 years old with a family history of heart disease I felt the exposure was too risky and while I was assured they could reduce the exposure they confirmed it would still have been exposed and receive possible damage. I decided at my age I needed my heart more than my breast. The 2nd reason was more an emotional one, my mother was diagnosed with breast cancer aged 42 and my desire (translate that to compulsive need) to do things differently. She was early stage like all of us so had a lumpectomy and radiation as her treatment. She developed metastic breast cancer, in her top rib behind the initial BC breast. Coincidentally all of her complications were also on her left side within the radiation exposure area, common sense says that of course they were weaker so when the body is fighting they won't hold up as well but it still played a big part in my decision.
If declining is something you are considering I'd strongly suggest you sit down with you oncologist and/or surgeon and discuss what they recommend instead and why. When I went back to them and said I don't want this, there was no judgement they just said OK how about this for a plan B. Do a heap of reading and go back with your reasons and suggestions and collaborate with your medical team, you will be able to come up with a treatment plan that they are satisfied with and works for you.
Good luck, Jen