I believe this to be correct, @Trikki2 ..... I never considered myself to be 'bigger breasted' (about size 34/14) ... I lay down on my chest for my rads, with boob hanging down thru a gap, which reduced rib exposure. Heart & lung were not mentioned as being a risk factor as this normally relates to the left side. I fully understand how heart & lungs could be an issue if lying on your back for the radiation - tho as mentioned earlier - holding their breath (as the actual ray treatment isn't all that long) for the treatment.