 The IMRT-MC2 study is a prospective, two armed, multicenter, randomized phase-III-trial comparing intensity modulated radiotherapy with integrated boost to conventional radiotherapy with consecutive boost in patients with breast cancer after breast conserving surgery. 502 patients will be recruited and randomized in two arms: patients in arm A will receive IMRT in 28 fractions delivering 50.4 Gy to the breast and 64.4 Gy to the tumor-bed by an integrated boost, while patients in arm B will receive conventional radiotherapy of the breast in 28 fractions to a dose of 50.4 Gy and a consecutive boost in 8 fractions to a total dose of 66.4 Gy. Primary aim of the study is the assessment of the cosmetic outcome and local control after breast radiotherapy. The study hypothesis is that intensity modulated radiotherapy IMRT is, in spite of the reduced treatment duration, at least equivalent to conventional therapy. 