Heart and Rads--Why so much pressure to have radiation?

I have looked thru the forum off and on for weeks trying to find information that I can use in my particular situation. Have not found it and am beginning to feel somewhat desperate. So hoping someone can chime in here.

I am scheduled for lumpectomy early next week. I had a core biopsy of a 1.2mm lesion that showed papillary carcinoma in situ. It sits in my left breast, just over the chest wall and directly over my heart. My oncologist said it may be upgraded after they have a chance to examine the entire specimen. It could be invasive, have other components. For now, they are not planning to do sentinel node nor am I a candidate at present for chemotherapy or endocrine therapy. The current plan is lumpectomy with 15 radiation treatments barring any surprises with the follow-on pathology. They are also planning to get an onco report on the tumor post surgery and I had gene testing but am not positive for that. However, a complicating factor in all this is the fact I had a terrible bout of viral pericarditis a year ago and have been left with a very erratic heart beat and possible scarring. I had a half dozen heart and lung CT scans last year and I remember thinking I hoped they were not giving me cancer . I doubt that is the case, but I had the equivalent of 12 years worth of radiation in a couple months and I am not young. While breast cancer may not be in my genes, familial cancer is widespread and I am having tests for that as well.

Along with my cancer team, I have a new cardiologist who is at the same university hospital that I saw for the first time two weeks ago. Only in the last few months have I been able to regain some semblance of my former muscle strength and energy levels. My heart is not working optimally and causes great waves of fatigue to wash over me still, plus I had a flare of my pericarditis just two months ago. So I am not keen to do anything that will make this worse or prolong my recovery. Since meeting the new cardiologist I have some hope that I might be restored to my former self--I have been receiving bad medical management of my heart condition and in the absence of other factors (I have zero cardiovascular disease, don't smoke or drink, good weight etc) I may eventually heal. I asked him point blank what his opinion of my treatment options was and he said obviously this is a personal decision, but he would favor treatment that did not include radiation.

As I understand it, even with in situ cancer if one has lumpectomy one must have radiation per current protocol. With a mastectomy I would not need radiation. Although my treatment team says they are supportive of any decision I might make in this regard I feel a lot of pressure to do lumpectomy and rads. Everyone keeps telling me that technology has changed dramatically in the past 10 years and I accept that. But no one can tell me the risk is zero to my heart and lungs. The radiation oncologist was not dismissive but not at all dissuaded from the idea that there is a possibility that the 15 or so treatments they propose could in any way injure my heart and lungs. ALL they can say, and it is like a mantra, that a mastectomy is a "big" surgery. So the hell what? What they are NOT saying is that radiation is without risk to your heart and the survival benefit to you is greater than mastectomy.

When I asked for statistics re what percentage of people DO have complications with their heart/lungs following radiation even with today's "heart sparing" techniques, the radiologist got very flustered and flat could not answer me.

I read somewhere a report on a study in Denmark or the Netherlands or maybe both that mastectomy was as good or superior to lumpectomy with rads and in older women, it seemed mastectomy conferred the better survival benefit.

I can't think of any downside to having a lumpectomy next week and then having a mastectomy other than the issue of two surgeries. Papillary cancer is rather difficult to assess from core biopsy and having the entire lesion is key to a definitive diagnosis. But people are acting like I am exaggerating the risks to my heart from follow on radiation treatments. I feel very, very confused. Actually, I feel like my head is going to explode...and so much pressure to make a decision on the side of the thing I most fear.